| Message ID | 20211111110043.101891-1-nuno.sa@analog.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | LTC2688 support | expand |
On Thu, 11 Nov 2021 12:00:42 +0100 Nuno Sá <nuno.sa@analog.com> wrote: Hi Nuno, > The reason why this is a RFC is because I'm still waiting for proper HW > to test this thing. The reason why I'm sending this already is because > there's some non usual features which might require extra ABI. Hence, > while waiting I thought we could already speed up the process in regards > with the ABI. Wise move as this is an unusual beast :) > > I still pushed the driver but the intent here is not really to review it. > Naturally, if someone already wants to give some feedback, that's very > much appreciated :) > > Now, there are three main interfaces depending on the channel mode: > 1) default (no new ABI) > 2) toggle mode > 3) dither mode > > The channel mode will be a devicetree property as it does not really > make much sense to change between modes at runtime even more because the > piece of HW we might want to control with a channel might be different > depending on the selected mode (I'm fairly sure on this between toggle > and other modes but not so sure between dither and default mode). I agree on toggle vs dither definitely being different, but normal you could implement either as software toggle, or dither with a 0 magnitude sine wave. So might not be worth implementing default mode at all. No harm in doing so though if there are advantages to having it. > > toggle mode special ABI: > > * Toggle operation enables fast switching of a DAC output between two > different DAC codes without any SPI transaction. Two codes are set in > input_a and input_b and then the output switches according to an input > signal (input_a -> clk high; input_b -> clk low). > > out_voltageY_input_register > - selects between input_a and input_b. After selecting one register, we > can write the dac code in out_voltageY_raw. > out_voltageY_toggle_en > - Disable/Enable toggle mode. The reason why I think this one is > important is because if we wanna change the 2 codes, we should first > disable this, set the codes and only then enable the mode back... > As I'm writing this, It kind of came to me that we can probably > achieve this with out_voltageY_powerdown attr (maybe takes a bit more > time to see the outputs but...) Hmm. These corner cases always take a bit of figuring out. What you have here is a bit 'device specific' for my liking. So there is precedence for ABI in this area, on the frequency devices but only for devices we still haven't moved out of staging. For those we needed a means to define selectable phases for PSK - where the selection was either software or, much like here, a selection pin. out_altvotage0_phase0 etc so I guess the equivalent here would be out_voltageY_raw0 out_voltageY_raw1 and the selection would be via something like out_voltageY_symbol (0 or 1 in this case). - note this is only relevant if you have the software toggle. Any enable needed for setting can be done as part of the write sequence for the raw0 / raw1 and should ideally not be exposed to userspace (controls that require manual sequencing tend to be hard to use / document). However, I'm not 100% sure it really maps to this case. What do you think? I'm not sure if whether a channel is in toggle mode is a circuit thing or not.. (and hence DT or userspace control?) Can see that even in a case where you did want to use external controls to pick the values, you might also want to override from software... Given there is a software toggle I guess we can use that as override. Actually that raises the question of what the point in having normal mode is? Can we just implement that as a software toggle toggle mode? One less thing to worry about if we can. There is also the question of whether selection of which toggle pin is used should be a dt thing or a userspace control... > > dither mode special ABI: > > * Dither operation adds a small sinusoidal wave to the digital DAC > signal path. Dithering is a signal processing technique that involves > the injection of ac noise to the signal path to reduce system > nonlinearities. > This is a complex feature to describe as (if I read it correctly) we have a dither clocked from an external pin, or in theory from software. That clock frequency must match the dither. Realistically that means it is a clock in our control or we have to match the period below to the frequency of that clock. > out_voltage0_dither_en > - Same as in toggle mode. > out_voltage0_dither_period > out_voltage0_dither_phase > - Period and phase of the signal. Only some values are valid so there's > also *_available files for these. I'm not sure if we can use the more > generic IIO_CHAN_INFO_PHASE and IIO_CHAN_INFO_FREQUENCY here as these > parameters don't really apply to the channel output signal.. Possibly not helpful to do so, but you could describe the channel as an out_altvoltage channel that happens to have a significant offset (the DC level) and phase, frequency etc as for a normal altvoltage channel. That would hide the intention here though so perhaps not a good plan even if it ensures we end up with standard ABI. > out_voltage0_input_register > - Same as in toggle mode. However in this mode the code set in the > input_b register has a special meaning. It's the amplitude of the > dither signal. Don't do that - provide a direct attribute representing the value of register_b and when it is written implicitly switch to the right register. Any ABI that requires a sequence of events is hard to use. > > One special mention to the dac scale. In this part this is something > that can be purely controlled by SW so that I'm allowing userspace to > change it rather then having it in dts. The available scales are: > > * [0 5V] -> offset 0 > * [0 10V] -> offset 0 > * [-5 5V] -> offset -32678 > * [-10 10V] -> offset -32768 > * [-15 15V] -> offset -32768 > > With the above, we also need to have the offset configurable and right > now I'm going to some trouble to make sure the scale + offset is > something valid. Honestly, I think I'm overdoing it because things can > still go wrong with [0 10V] and [-5 5V] as the scales are the same > here. Furthermore, there's no real arm that can be done to the HW. Is > just that the readings won't match with what someone might be expecting. > My plan is to just remove those checks and assume is up to userspace to > make it right and not have [-10 10V] scale with 0 offset for example. So this is something we've debated a few times in the past. There is a fairly strong argument for output devices that the range is a characteristic of the circuit. At the very least it makes sense to restrict it in DT even if we allow safe forms of tweaking in the driver. For an initial driver, I'd just have it in DT. Jonathan > > I know that I'm taking a shortcut here :) so if you prefer to only > discuss this in the __real__ series, I totally get it. It's a fine short cut to take - I send out RFCs all the time for similar open questions! Jonathan > > https://www.analog.com/media/en/technical-documentation/data-sheets/ltc2688.pdf > > - Nuno Sá > > Nuno Sá (1): > iio: dac: add support for ltc2688 > > drivers/iio/dac/ltc2688.c | 995 ++++++++++++++++++++++++++++++++++++++ > 1 file changed, 995 insertions(+) > create mode 100644 drivers/iio/dac/ltc2688.c >
Hi Jonathan, Thanks for your inputs... > From: Jonathan Cameron <jic23@kernel.org> > Sent: Friday, November 12, 2021 5:15 PM > To: Sa, Nuno <Nuno.Sa@analog.com> > Cc: linux-iio@vger.kernel.org > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > [External] > > On Thu, 11 Nov 2021 12:00:42 +0100 > Nuno Sá <nuno.sa@analog.com> wrote: > > Hi Nuno, > > > The reason why this is a RFC is because I'm still waiting for proper HW > > to test this thing. The reason why I'm sending this already is because > > there's some non usual features which might require extra ABI. > Hence, > > while waiting I thought we could already speed up the process in > regards > > with the ABI. > > Wise move as this is an unusual beast :) > > > > > I still pushed the driver but the intent here is not really to review it. > > Naturally, if someone already wants to give some feedback, that's > very > > much appreciated :) > > > > > Now, there are three main interfaces depending on the channel > mode: > > 1) default (no new ABI) > > 2) toggle mode > > 3) dither mode > > > > The channel mode will be a devicetree property as it does not really > > make much sense to change between modes at runtime even more > because the > > piece of HW we might want to control with a channel might be > different > > depending on the selected mode (I'm fairly sure on this between > toggle > > and other modes but not so sure between dither and default mode). > > I agree on toggle vs dither definitely being different, but normal you > could implement either as software toggle, or dither with a 0 > magnitude > sine wave. So might not be worth implementing default mode at all. > No harm in doing so though if there are advantages to having it. My feeling is that we could probably have dither as the "default mode". More on this below... > > > > toggle mode special ABI: > > > > * Toggle operation enables fast switching of a DAC output between > two > > different DAC codes without any SPI transaction. Two codes are set > in > > input_a and input_b and then the output switches according to an > input > > signal (input_a -> clk high; input_b -> clk low). > > > > out_voltageY_input_register > > - selects between input_a and input_b. After selecting one register, > we > > can write the dac code in out_voltageY_raw. > > out_voltageY_toggle_en > > - Disable/Enable toggle mode. The reason why I think this one is > > important is because if we wanna change the 2 codes, we should > first > > disable this, set the codes and only then enable the mode back... > > As I'm writing this, It kind of came to me that we can probably > > achieve this with out_voltageY_powerdown attr (maybe takes a bit > more > > time to see the outputs but...) > > Hmm. These corner cases always take a bit of figuring out. What you > have > here is a bit 'device specific' for my liking. > > So there is precedence for ABI in this area, on the frequency devices > but only > for devices we still haven't moved out of staging. For those we > needed a means > to define selectable phases for PSK - where the selection was either > software or, > much like here, a selection pin. > > out_altvotage0_phase0 etc > > so I guess the equivalent here would be > out_voltageY_raw0 > out_voltageY_raw1 > and the selection would be via something like > out_voltageY_symbol (0 or 1 in this case). - note this is only > relevant if you have the software toggle. Any enable needed for > setting > can be done as part of the write sequence for the raw0 / raw1 and > should > ideally not be exposed to userspace (controls that require manual > sequencing > tend to be hard to use / document). Yeah, I thought about that. I was even thinking in having something like *_amplitude for dither mode. In some cases, where we might be left in some non obvious state (eg: moved the select register to input b and then we failed to set the code;), I prefer to leave things as flexible as possible for userspace. But I agree it adds up more complexity and in this case, I can just always go to 'input_a' when writing 'raw0'... > However, I'm not 100% sure it really maps to this case. What do you > think? I think it can work. Though out_voltageY_symbol probably needs to be shared by type to be coherent with what we might have with TGPx. Note the sw_toggle register has a bit mask of the channels we want to toggle which means we can toggle multiple channels at the same time. It works the same with TGPx if you map multiple channels to the same pin. There's also the question on how to handle this if a TGPx is provided? I guess it will just override the pin... But most likely having them both at the same time will lead to non desired results (unless we have a way to gate/ungate the clocks)... > I'm not sure if whether a channel is in toggle mode is a circuit thing or > not.. > (and hence DT or userspace control?) The only reason I can think off to have it as DT is that toggle mode seems to be for more specific use cases so I guess the HW we want to control ( and connect to a toggle enabled channel) will be different. I'm also not seeing an use case for ping ponging between the modes mostly because of the above... > Can see that even in a case where you did want to use external > controls to > pick the values, you might also want to override from software... > Given there is a software toggle I guess we can use that as override. > Actually that raises the question of what the point in having normal > mode is? > Can we just implement that as a software toggle toggle mode? One > less thing to > worry about if we can. I did thought about the sw_toggle thing (it's something that is only valid for channels in dither/toggle mode). My reasoning was that either 1) I did not supported it and made the TGPx selection mandatory (in case dither/toggle mode enabled) or 2) I did support it and hence the pins are not really mandatory. I went with 1) because, honestly, I'm not seeing the point of having these modes and use sw toggle (at least on a production system). However, if we want to get rid of the default mode and have it as the dither mode, I agree we need sw_toggle because If someone just wants to use the channel without any dithering, we can't have an hard requirement to provide a external TGPx. Moreover, if the default channel will be a dither capable one, we need to provide full functionality and hence, sw_toggle. As I stated before, I'm just not sure on how to handle things if a TGPx is also provided. Maybe they should be mutual exclusive? I mean, if someone tries to toggle a channel with a mapped TGPx we return some error code? > There is also the question of whether selection of which toggle pin is > used > should be a dt thing or a userspace control... Well, this definitely means some HW wiring to have the external signals and I'm not sure if there's any added valuable in being able to change the external signal at runtime? > > > > dither mode special ABI: > > > > * Dither operation adds a small sinusoidal wave to the digital DAC > > signal path. Dithering is a signal processing technique that involves > > the injection of ac noise to the signal path to reduce system > > nonlinearities. > > > > This is a complex feature to describe as (if I read it correctly) we have > a dither clocked from an external pin, or in theory from software. That > clock > frequency must match the dither. Realistically that means it is a clock > in our control or we have to match the period below to the frequency > of that > clock. Yeah, the frequency of the dither signal is fsig = fclk / N, where N can only be: [4 8 16 32 64]. So, we kind of just have these available options for the signal frequency and fclk is something we can control and know (assuming we have TGPx mapping which I'm bundling with a clk). The only quirk with having this with frequency rather than raw N is to handle the sw_toggle where we have no idea about fclk? We could also think of this attr as some kind of decimation... > > out_voltage0_dither_en > > - Same as in toggle mode. > > out_voltage0_dither_period > > out_voltage0_dither_phase > > - Period and phase of the signal. Only some values are valid so > there's > > also *_available files for these. I'm not sure if we can use the more > > generic IIO_CHAN_INFO_PHASE and IIO_CHAN_INFO_FREQUENCY > here as these > > parameters don't really apply to the channel output signal.. > > Possibly not helpful to do so, but you could describe the channel as an > out_altvoltage channel that happens to have a significant offset (the > DC > level) and phase, frequency etc as for a normal altvoltage channel. > That would hide the intention here though so perhaps not a good plan > even if it ensures we end up with standard ABI. I think altvoltage might not be optimal here because the phase and frequency are really not characteristics of the output signal of the channel. > > out_voltage0_input_register > > - Same as in toggle mode. However in this mode the code set in the > > input_b register has a special meaning. It's the amplitude of the > > dither signal. > Don't do that - provide a direct attribute representing the value of > register_b and when it is written implicitly switch to the right register. > Any ABI that requires a sequence of events is hard to use. I guess we can just use the same raw1 attr here? Even though, in dither mode this has special meaning (it is the amplitude)... > > > > > One special mention to the dac scale. In this part this is something > > that can be purely controlled by SW so that I'm allowing userspace to > > change it rather then having it in dts. The available scales are: > > > > * [0 5V] -> offset 0 > > * [0 10V] -> offset 0 > > * [-5 5V] -> offset -32678 > > * [-10 10V] -> offset -32768 > > * [-15 15V] -> offset -32768 > > > > With the above, we also need to have the offset configurable and > right > > now I'm going to some trouble to make sure the scale + offset is > > something valid. Honestly, I think I'm overdoing it because things can > > still go wrong with [0 10V] and [-5 5V] as the scales are the same > > here. Furthermore, there's no real arm that can be done to the HW. > Is > > just that the readings won't match with what someone might be > expecting. > > My plan is to just remove those checks and assume is up to > userspace to > > make it right and not have [-10 10V] scale with 0 offset for example. > > So this is something we've debated a few times in the past. > There is a fairly strong argument for output devices that the range is > a characteristic of the circuit. At the very least it makes sense to > restrict it in DT even if we allow safe forms of tweaking in the driver. > For an initial driver, I'd just have it in DT. > No complaints against that and makes things way simpler to handle. - Nuno Sá
On Mon, 15 Nov 2021 10:28:51 +0000 "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > Hi Jonathan, > > Thanks for your inputs... > > > From: Jonathan Cameron <jic23@kernel.org> > > Sent: Friday, November 12, 2021 5:15 PM > > To: Sa, Nuno <Nuno.Sa@analog.com> > > Cc: linux-iio@vger.kernel.org > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > [External] > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > Hi Nuno, > > > > > The reason why this is a RFC is because I'm still waiting for proper HW > > > to test this thing. The reason why I'm sending this already is because > > > there's some non usual features which might require extra ABI. > > Hence, > > > while waiting I thought we could already speed up the process in > > regards > > > with the ABI. > > > > Wise move as this is an unusual beast :) > > > > > > > > I still pushed the driver but the intent here is not really to review it. > > > Naturally, if someone already wants to give some feedback, that's > > very > > > much appreciated :) > > > > > > > > Now, there are three main interfaces depending on the channel > > mode: > > > 1) default (no new ABI) > > > 2) toggle mode > > > 3) dither mode > > > > > > The channel mode will be a devicetree property as it does not really > > > make much sense to change between modes at runtime even more > > because the > > > piece of HW we might want to control with a channel might be > > different > > > depending on the selected mode (I'm fairly sure on this between > > toggle > > > and other modes but not so sure between dither and default mode). > > > > I agree on toggle vs dither definitely being different, but normal you > > could implement either as software toggle, or dither with a 0 > > magnitude > > sine wave. So might not be worth implementing default mode at all. > > No harm in doing so though if there are advantages to having it. > > My feeling is that we could probably have dither as the "default mode". > More on this below... > > > > > > > toggle mode special ABI: > > > > > > * Toggle operation enables fast switching of a DAC output between > > two > > > different DAC codes without any SPI transaction. Two codes are set > > in > > > input_a and input_b and then the output switches according to an > > input > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > out_voltageY_input_register > > > - selects between input_a and input_b. After selecting one register, > > we > > > can write the dac code in out_voltageY_raw. > > > out_voltageY_toggle_en > > > - Disable/Enable toggle mode. The reason why I think this one is > > > important is because if we wanna change the 2 codes, we should > > first > > > disable this, set the codes and only then enable the mode back... > > > As I'm writing this, It kind of came to me that we can probably > > > achieve this with out_voltageY_powerdown attr (maybe takes a bit > > more > > > time to see the outputs but...) > > > > Hmm. These corner cases always take a bit of figuring out. What you > > have > > here is a bit 'device specific' for my liking. > > > > So there is precedence for ABI in this area, on the frequency devices > > but only > > for devices we still haven't moved out of staging. For those we > > needed a means > > to define selectable phases for PSK - where the selection was either > > software or, > > much like here, a selection pin. > > > > out_altvotage0_phase0 etc > > > > so I guess the equivalent here would be > > out_voltageY_raw0 > > out_voltageY_raw1 > > and the selection would be via something like > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > relevant if you have the software toggle. Any enable needed for > > setting > > can be done as part of the write sequence for the raw0 / raw1 and > > should > > ideally not be exposed to userspace (controls that require manual > > sequencing > > tend to be hard to use / document). > > Yeah, I thought about that. I was even thinking in having something like > *_amplitude for dither mode. In some cases, where we might be left > in some non obvious state (eg: moved the select register to input b and > then we failed to set the code;), I prefer to leave things as flexible as > possible for userspace. But I agree it adds up more complexity and in > this case, I can just always go to 'input_a' when writing 'raw0'... > > > However, I'm not 100% sure it really maps to this case. What do you > > think? > > I think it can work. Though out_voltageY_symbol probably needs to be > shared by type to be coherent with what we might have with TGPx. That's fine. > Note the sw_toggle register has a bit mask of the channels we want to > toggle which means we can toggle multiple channels at the same time. Using that wired up to buffer mode might make sense. You'd provide multiple buffers and allow channels to be selected into one of them at a time. Each buffer is then tied to a different toggle (TGP0, TGP1, etc) The same could be true for the software toggle. It'll get a bit fiddly though. Perhaps this is an advanced feature to think about later... > It works the same with TGPx if you map multiple channels to the same > pin. > > There's also the question on how to handle this if a TGPx is provided? > I guess it will just override the pin... But most likely having them both > at the same time will lead to non desired results (unless we have a > way to gate/ungate the clocks)... I don't follow this bit. You mean TGPx and software toggle. As far as I can tell it's an either/or thing per channel. > > > I'm not sure if whether a channel is in toggle mode is a circuit thing or > > not.. > > (and hence DT or userspace control?) > > The only reason I can think off to have it as DT is that toggle mode seems > to be for more specific use cases so I guess the HW we want to control ( > and connect to a toggle enabled channel) will be different. > > I'm also not seeing an use case for ping ponging between the modes mostly > because of the above... Only use I can see is to reduce traffic if you happen to be switching between two sets of DAC outputs repeatedly. If there wasn't an LDAC pin I'd suspect this was there to enable simultaneous updates but we have that anyway. Maybe if the LDAC isn't wired this could be used to provide similar functionality? If that's the case, we could just leave it as a possible TODO if anyone wants it in future... I think you could use the TGPx to provide controlled switching of sets of channels. Maybe that's something useful? > > > Can see that even in a case where you did want to use external > > controls to > > pick the values, you might also want to override from software... > > Given there is a software toggle I guess we can use that as override. > > Actually that raises the question of what the point in having normal > > mode is? > > Can we just implement that as a software toggle toggle mode? One > > less thing to > > worry about if we can. > > I did thought about the sw_toggle thing (it's something that is only valid > for channels in dither/toggle mode). My reasoning was that either > > 1) I did not supported it and made the TGPx selection mandatory (in case > dither/toggle mode enabled) or > 2) I did support it and hence the pins are not really mandatory. > > I went with 1) because, honestly, I'm not seeing the point of having these > modes and use sw toggle (at least on a production system). However, if we > want to get rid of the default mode and have it as the dither mode, I agree > we need sw_toggle because If someone just wants to use the channel > without any dithering, we can't have an hard requirement to provide a > external TGPx. Moreover, if the default channel will be a dither capable > one, we need to provide full functionality and hence, sw_toggle. > > As I stated before, I'm just not sure on how to handle things if a TGPx is > also provided. Maybe they should be mutual exclusive? I mean, if someone > tries to toggle a channel with a mapped TGPx we return some error code? Given the mapping of TGPx to channel is a software control I think ultimately you'd want to expose that - one way I can think of doing that is via the buffer interface. 4x buffers. One of each TGP0,1,2 and SW toggle. Enable the channels you want for a given 'buffer' and then they will switch together based on the data in the buffer. If the buffer has a series of toggling values then it's simple - if not then after each toggle the buffer would need to preload the next value. The snag there is that you'd need to know a toggle occurred and if the toggle pins are wired to somewhere other than our host I'm not sure how you would know that in general? (could wire the same TGPx signal to an interrupt on the host controller but seems unlikely). Whether software toggle is worth bothering when we have LDAC to control simultaneous DAC updates isn't clear to me. I guess it's fewer writes if we happen to be cycling between values. Perhaps you are right and that feature is just for debug. > > > There is also the question of whether selection of which toggle pin is > > used > > should be a dt thing or a userspace control... > > Well, this definitely means some HW wiring to have the external signals and > I'm not sure if there's any added valuable in being able to change the > external signal at runtime? Whilst I can conjecture reasons to do this, you may well be right - real usecases will know which signal groups they want to control together. > > > > > > > dither mode special ABI: > > > > > > * Dither operation adds a small sinusoidal wave to the digital DAC > > > signal path. Dithering is a signal processing technique that involves > > > the injection of ac noise to the signal path to reduce system > > > nonlinearities. > > > > > > > This is a complex feature to describe as (if I read it correctly) we have > > a dither clocked from an external pin, or in theory from software. That > > clock > > frequency must match the dither. Realistically that means it is a clock > > in our control or we have to match the period below to the frequency > > of that > > clock. > > Yeah, the frequency of the dither signal is fsig = fclk / N, where N can only > be: [4 8 16 32 64]. So, we kind of just have these available options for the > signal frequency and fclk is something we can control and know (assuming > we have TGPx mapping which I'm bundling with a clk). > > The only quirk with having this with frequency rather than raw N is > to handle the sw_toggle where we have no idea about fclk? We could also > think of this attr as some kind of decimation... Does seems unlikely anyone would use dither with a sw toggle. Perhaps best plan here is to not support that combination. As to the clock, these are about controlling a sine wave frequency. I'm not sure decimation fits as a model. (figure 19) Given you know the input clock, perhaps present this as something like out_voltage0_dither_frequency I don't thing dithers are always this simple, so probably want to be specific its a sine wave so maybe we need out_voltage0_dither_type 'sine' We used to have some DDS chips in staging but looks like they all got dropped due to end of time Those had various waveforms and IIRC all we came up with was descriptive terms + frequencies and magnitudes. > > > > out_voltage0_dither_en > > > - Same as in toggle mode. > > > out_voltage0_dither_period > > > out_voltage0_dither_phase > > > - Period and phase of the signal. Only some values are valid so > > there's > > > also *_available files for these. I'm not sure if we can use the more > > > generic IIO_CHAN_INFO_PHASE and IIO_CHAN_INFO_FREQUENCY > > here as these > > > parameters don't really apply to the channel output signal.. > > > > Possibly not helpful to do so, but you could describe the channel as an > > out_altvoltage channel that happens to have a significant offset (the > > DC > > level) and phase, frequency etc as for a normal altvoltage channel. > > That would hide the intention here though so perhaps not a good plan > > even if it ensures we end up with standard ABI. > > I think altvoltage might not be optimal here because the phase and frequency > are really not characteristics of the output signal of the channel. Well they kind of are if you set the magnitude high enough - but I get your point. That's not how they are intended to be used. > > > > out_voltage0_input_register > > > - Same as in toggle mode. However in this mode the code set in the > > > input_b register has a special meaning. It's the amplitude of the > > > dither signal. > > Don't do that - provide a direct attribute representing the value of > > register_b and when it is written implicitly switch to the right register. > > Any ABI that requires a sequence of events is hard to use. > > I guess we can just use the same raw1 attr here? Even though, in dither > mode this has special meaning (it is the amplitude)... I was thinking toggle mode here. This interface doesn't work for dither. in that case there is just out_voltage0_raw for the DC part and out_voltage0_dither_raw for the dither amplitude. Assumption being same scaling as I don't really want to support multiple scale factors if we can avoid it. > > > > > > > > > One special mention to the dac scale. In this part this is something > > > that can be purely controlled by SW so that I'm allowing userspace to > > > change it rather then having it in dts. The available scales are: > > > > > > * [0 5V] -> offset 0 > > > * [0 10V] -> offset 0 > > > * [-5 5V] -> offset -32678 > > > * [-10 10V] -> offset -32768 > > > * [-15 15V] -> offset -32768 > > > > > > With the above, we also need to have the offset configurable and > > right > > > now I'm going to some trouble to make sure the scale + offset is > > > something valid. Honestly, I think I'm overdoing it because things can > > > still go wrong with [0 10V] and [-5 5V] as the scales are the same > > > here. Furthermore, there's no real arm that can be done to the HW. > > Is > > > just that the readings won't match with what someone might be > > expecting. > > > My plan is to just remove those checks and assume is up to > > userspace to > > > make it right and not have [-10 10V] scale with 0 offset for example. > > > > So this is something we've debated a few times in the past. > > There is a fairly strong argument for output devices that the range is > > a characteristic of the circuit. At the very least it makes sense to > > restrict it in DT even if we allow safe forms of tweaking in the driver. > > For an initial driver, I'd just have it in DT. > > > > No complaints against that and makes things way simpler to handle. Great. > > - Nuno Sá > So conclusions.. Hmm. Not strong ones yet, but for dither mode at least I think you want to link particular channels to a TGPx choice out_voltage0_raw out_voltage0_raw_available ( nice to have on DACs) out_voltage0_scale out_voltage0_dither_raw out_voltage0_dither_raw_available out_voltage0_dither_frequency out_voltage0_dither_frequency_available out_voltage0_dither_phase out_voltage0_dither_phase_available Toggle mode is less clear to me but symbol approach plus TGPx in DT maybe works You could allow for software override to set the symbol. Interface to unset it being to write an empty string to _symbol. Maybe leave that for now. out_voltage0_raw0 out_voltage0_raw1 out_voltage0_scale out_voltage0_symbol Perhaps that's enough for an initial driver and we can think more or complex corner cases after that is in place? Jonathan
> -----Original Message----- > From: Jonathan Cameron <jic23@kernel.org> > Sent: Sunday, November 21, 2021 1:18 PM > To: Sa, Nuno <Nuno.Sa@analog.com> > Cc: linux-iio@vger.kernel.org > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > [External] > > On Mon, 15 Nov 2021 10:28:51 +0000 > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > Hi Jonathan, > > > > Thanks for your inputs... > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > Sent: Friday, November 12, 2021 5:15 PM > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > Cc: linux-iio@vger.kernel.org > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > [External] > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > Hi Nuno, > > > > > > > The reason why this is a RFC is because I'm still waiting for proper > HW > > > > to test this thing. The reason why I'm sending this already is > because > > > > there's some non usual features which might require extra ABI. > > > Hence, > > > > while waiting I thought we could already speed up the process in > > > regards > > > > with the ABI. > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > I still pushed the driver but the intent here is not really to review > it. > > > > Naturally, if someone already wants to give some feedback, > that's > > > very > > > > much appreciated :) > > > > > > > > > > > Now, there are three main interfaces depending on the channel > > > mode: > > > > 1) default (no new ABI) > > > > 2) toggle mode > > > > 3) dither mode > > > > > > > > The channel mode will be a devicetree property as it does not > really > > > > make much sense to change between modes at runtime even > more > > > because the > > > > piece of HW we might want to control with a channel might be > > > different > > > > depending on the selected mode (I'm fairly sure on this between > > > toggle > > > > and other modes but not so sure between dither and default > mode). > > > > > > I agree on toggle vs dither definitely being different, but normal > you > > > could implement either as software toggle, or dither with a 0 > > > magnitude > > > sine wave. So might not be worth implementing default mode at > all. > > > No harm in doing so though if there are advantages to having it. > > > > My feeling is that we could probably have dither as the "default > mode". > > More on this below... > > > > > > > > > > toggle mode special ABI: > > > > > > > > * Toggle operation enables fast switching of a DAC output > between > > > two > > > > different DAC codes without any SPI transaction. Two codes are > set > > > in > > > > input_a and input_b and then the output switches according to > an > > > input > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > out_voltageY_input_register > > > > - selects between input_a and input_b. After selecting one > register, > > > we > > > > can write the dac code in out_voltageY_raw. > > > > out_voltageY_toggle_en > > > > - Disable/Enable toggle mode. The reason why I think this one is > > > > important is because if we wanna change the 2 codes, we > should > > > first > > > > disable this, set the codes and only then enable the mode > back... > > > > As I'm writing this, It kind of came to me that we can probably > > > > achieve this with out_voltageY_powerdown attr (maybe takes a > bit > > > more > > > > time to see the outputs but...) > > > > > > Hmm. These corner cases always take a bit of figuring out. What > you > > > have > > > here is a bit 'device specific' for my liking. > > > > > > So there is precedence for ABI in this area, on the frequency > devices > > > but only > > > for devices we still haven't moved out of staging. For those we > > > needed a means > > > to define selectable phases for PSK - where the selection was > either > > > software or, > > > much like here, a selection pin. > > > > > > out_altvotage0_phase0 etc > > > > > > so I guess the equivalent here would be > > > out_voltageY_raw0 > > > out_voltageY_raw1 > > > and the selection would be via something like > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > relevant if you have the software toggle. Any enable needed for > > > setting > > > can be done as part of the write sequence for the raw0 / raw1 and > > > should > > > ideally not be exposed to userspace (controls that require manual > > > sequencing > > > tend to be hard to use / document). > > > > Yeah, I thought about that. I was even thinking in having something > like > > *_amplitude for dither mode. In some cases, where we might be left > > in some non obvious state (eg: moved the select register to input b > and > > then we failed to set the code;), I prefer to leave things as flexible as > > possible for userspace. But I agree it adds up more complexity and in > > this case, I can just always go to 'input_a' when writing 'raw0'... > > > > > However, I'm not 100% sure it really maps to this case. What do > you > > > think? > > > > I think it can work. Though out_voltageY_symbol probably needs to > be > > shared by type to be coherent with what we might have with TGPx. > > That's fine. > > > Note the sw_toggle register has a bit mask of the channels we want > to > > toggle which means we can toggle multiple channels at the same > time. > > Using that wired up to buffer mode might make sense. You'd provide > multiple > buffers and allow channels to be selected into one of them at a time. > Each > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > The same could be true for the software toggle. It'll get a bit fiddly > though. > > Perhaps this is an advanced feature to think about later... > > > It works the same with TGPx if you map multiple channels to the > same > > pin. > > > > There's also the question on how to handle this if a TGPx is provided? > > I guess it will just override the pin... But most likely having them both > > at the same time will lead to non desired results (unless we have a > > way to gate/ungate the clocks)... > I don't follow this bit. You mean TGPx and software toggle. As far as I > can > tell it's an either/or thing per channel. > Here I meant that if we have a TGPx pin bundled to some channel(s) we do not want to also dance with the sw_toggle bit of that channel. Ultimately, that's on the user responsibility but we could also add some guards I guess. I'm not sure if it's an either/or thing per channel... IIUC, we spoke about making dither and default mode the same. That might complicate things a bit as: 1) We should not force a user to specify a TGPx pin for those channels (since it can also work with dithering disabled). 2) Because of 1), we should also support sw_toggle for these channels since someone might want to enable dither mode (at runtime) and the TGPx pin was not given. Hence, we need to have a way to update the DAC using the sw_toggle. Did I understood things wrong? One thing that comes to my mind, is to return error (eg: EPERM or ENOTSUPP) if someone tries to enable dither mode and no TGPx pin was selected for that channel? Hence, we do not need to add the sw_toggle ABI (out_voltage_symbol) for the default/dither mode. Or maybe even better, we just expose the dither ABI if a TGPx pin is given over dt (I try to explain the toggle/dither modes below; that might help you in understanding my reasoning here)? Alternatively, we just keep the approach I have in this RFC and we keep the 3 different modes (being mode a dt property; in the current state I'm using a boolean to say a channel Is in toggle mode)... Maybe with the difference that we allow sw_toggle for toggle enabled channels. > > > > > I'm not sure if whether a channel is in toggle mode is a circuit thing > or > > > not.. > > > (and hence DT or userspace control?) > > > > The only reason I can think off to have it as DT is that toggle mode > seems > > to be for more specific use cases so I guess the HW we want to > control ( > > and connect to a toggle enabled channel) will be different. > > > > I'm also not seeing an use case for ping ponging between the modes > mostly > > because of the above... > > Only use I can see is to reduce traffic if you happen to be switching > between > two sets of DAC outputs repeatedly. If there wasn't an LDAC pin I'd > suspect > this was there to enable simultaneous updates but we have that > anyway. > Maybe if the LDAC isn't wired this could be used to provide similar > functionality? If that's the case, we could just leave it as a possible > TODO if anyone wants it in future... > I think you could use the TGPx to provide controlled switching of > sets of channels. Maybe that's something useful? Hmm, I think LDAC is something else. The LDAC pin updates all 16 channels with the value of the input register (which I assume is INPUT_A) independent of them being in dither/toggle mode. Honestly, I'm not even sure of how thing would work if someone plays with LDAC + channels in dither/toggle mode. I think extra care would be needed... So, TGPx pins are indeed used to control set of channels. But note that these pins (as sw_toggle) are only meaningful if the channel is in dither or toggle mode (the channel bit in the toggle/dither enable register has to be set): * In toggle mode we have two set of input registers: INPUT_A and INPUT_B and we toggle between these two values. If we wire a TGPx pin and bundle it to a toggle enabled channel, when the input signal is high, we output INPUT_A and INPUT_B when the signal is low. We can mimic the same behavior by writing 1/0 to the sw_toggle register. * In dither mode, things are slightly different as INPUT_B is the value for the sinusoidal amplitude. And if we have an external signal on a TGPx pin, the dac channel is updated on the rising edge of the signal. Again, we can mimic the same behavior with the sw_toggle register. So, for dither mode, I'm not really seeing why someone would want to use the sw_toggle. Even for toggle mode, I have my doubts but I can more easily see it. > > > > > Can see that even in a case where you did want to use external > > > controls to > > > pick the values, you might also want to override from software... > > > Given there is a software toggle I guess we can use that as > override. > > > Actually that raises the question of what the point in having normal > > > mode is? > > > Can we just implement that as a software toggle toggle mode? One > > > less thing to > > > worry about if we can. > > > > I did thought about the sw_toggle thing (it's something that is only > valid > > for channels in dither/toggle mode). My reasoning was that either > > > > 1) I did not supported it and made the TGPx selection mandatory (in > case > > dither/toggle mode enabled) or > > 2) I did support it and hence the pins are not really mandatory. > > > > I went with 1) because, honestly, I'm not seeing the point of having > these > > modes and use sw toggle (at least on a production system). > However, if we > > want to get rid of the default mode and have it as the dither mode, I > agree > > we need sw_toggle because If someone just wants to use the > channel > > without any dithering, we can't have an hard requirement to provide > a > > external TGPx. Moreover, if the default channel will be a dither > capable > > one, we need to provide full functionality and hence, sw_toggle. > > > > As I stated before, I'm just not sure on how to handle things if a TGPx > is > > also provided. Maybe they should be mutual exclusive? I mean, if > someone > > tries to toggle a channel with a mapped TGPx we return some error > code? > > Given the mapping of TGPx to channel is a software control I think > ultimately > you'd want to expose that - one way I can think of doing that is via > the buffer interface. > > 4x buffers. One of each TGP0,1,2 and SW toggle. Enable the channels > you > want for a given 'buffer' and then they will switch together based on > the > data in the buffer. If the buffer has a series of toggling values then > it's simple - if not then after each toggle the buffer would need to > preload > the next value. The snag there is that you'd need to know a toggle > occurred > and if the toggle pins are wired to somewhere other than our host I'm > not sure > how you would know that in general? (could wire the same TGPx signal > to an > interrupt on the host controller but seems unlikely). Honestly I think that we would be probably over engineering things with this even though I get your point. OTOH, as you said, the triggering would be very hacky to handle and that might already tell us something :) > Whether software toggle is worth bothering when we have LDAC to > control > simultaneous DAC updates isn't clear to me. I guess it's fewer writes Hopefully I could make it clear that sw_toggle is something else than LDAC :) > if we happen to be cycling between values. Perhaps you are right and > that > feature is just for debug. > > > > > > There is also the question of whether selection of which toggle pin > is > > > used > > > should be a dt thing or a userspace control... > > > > Well, this definitely means some HW wiring to have the external > signals and > > I'm not sure if there's any added valuable in being able to change the > > external signal at runtime? > > Whilst I can conjecture reasons to do this, you may well be right - real > usecases will know which signal groups they want to control together. > > > > > > > > > > > dither mode special ABI: > > > > > > > > * Dither operation adds a small sinusoidal wave to the digital DAC > > > > signal path. Dithering is a signal processing technique that > involves > > > > the injection of ac noise to the signal path to reduce system > > > > nonlinearities. > > > > > > > > > > This is a complex feature to describe as (if I read it correctly) we > have > > > a dither clocked from an external pin, or in theory from software. > That > > > clock > > > frequency must match the dither. Realistically that means it is a > clock > > > in our control or we have to match the period below to the > frequency > > > of that > > > clock. > > > > Yeah, the frequency of the dither signal is fsig = fclk / N, where N can > only > > be: [4 8 16 32 64]. So, we kind of just have these available options for > the > > signal frequency and fclk is something we can control and know > (assuming > > we have TGPx mapping which I'm bundling with a clk). > > > > The only quirk with having this with frequency rather than raw N is > > to handle the sw_toggle where we have no idea about fclk? We > could also > > think of this attr as some kind of decimation... > > Does seems unlikely anyone would use dither with a sw toggle. > Perhaps best plan here is to not support that combination. Agree... But there are some subtleties that we need to settle about the channel default mode as I raised in my previous comments. > As to the clock, these are about controlling a sine wave frequency. I'm > not sure > decimation fits as a model. (figure 19) > > Given you know the input clock, perhaps present this as something like > out_voltage0_dither_frequency > > I don't thing dithers are always this simple, so probably want to be > specific its > a sine wave so maybe we need > out_voltage0_dither_type 'sine' > > We used to have some DDS chips in staging but looks like they all got > dropped due > to end of time Those had various waveforms and IIRC all we came up > with was > descriptive terms + frequencies and magnitudes. > > > > > > > > out_voltage0_dither_en > > > > - Same as in toggle mode. > > > > out_voltage0_dither_period > > > > out_voltage0_dither_phase > > > > - Period and phase of the signal. Only some values are valid so > > > there's > > > > also *_available files for these. I'm not sure if we can use the > more > > > > generic IIO_CHAN_INFO_PHASE and > IIO_CHAN_INFO_FREQUENCY > > > here as these > > > > parameters don't really apply to the channel output signal.. > > > > > > Possibly not helpful to do so, but you could describe the channel as > an > > > out_altvoltage channel that happens to have a significant offset > (the > > > DC > > > level) and phase, frequency etc as for a normal altvoltage channel. > > > That would hide the intention here though so perhaps not a good > plan > > > even if it ensures we end up with standard ABI. > > > > I think altvoltage might not be optimal here because the phase and > frequency > > are really not characteristics of the output signal of the channel. > > Well they kind of are if you set the magnitude high enough - but I get > your > point. That's not how they are intended to be used. > > > > > > > out_voltage0_input_register > > > > - Same as in toggle mode. However in this mode the code set in > the > > > > input_b register has a special meaning. It's the amplitude of the > > > > dither signal. > > > Don't do that - provide a direct attribute representing the value of > > > register_b and when it is written implicitly switch to the right > register. > > > Any ABI that requires a sequence of events is hard to use. > > > > I guess we can just use the same raw1 attr here? Even though, in > dither > > mode this has special meaning (it is the amplitude)... > > I was thinking toggle mode here. This interface doesn't work for dither. > in that case there is just > out_voltage0_raw for the DC part and > out_voltage0_dither_raw for the dither amplitude. Assumption being > same scaling > as I don't really want to support multiple scale factors if we can avoid it. I'm fairly sure it is the same scaling.... > > > > > > > > > > > > > > > One special mention to the dac scale. In this part this is something > > > > that can be purely controlled by SW so that I'm allowing > userspace to > > > > change it rather then having it in dts. The available scales are: > > > > > > > > * [0 5V] -> offset 0 > > > > * [0 10V] -> offset 0 > > > > * [-5 5V] -> offset -32678 > > > > * [-10 10V] -> offset -32768 > > > > * [-15 15V] -> offset -32768 > > > > > > > > With the above, we also need to have the offset configurable > and > > > right > > > > now I'm going to some trouble to make sure the scale + offset is > > > > something valid. Honestly, I think I'm overdoing it because things > can > > > > still go wrong with [0 10V] and [-5 5V] as the scales are the same > > > > here. Furthermore, there's no real arm that can be done to the > HW. > > > Is > > > > just that the readings won't match with what someone might be > > > expecting. > > > > My plan is to just remove those checks and assume is up to > > > userspace to > > > > make it right and not have [-10 10V] scale with 0 offset for > example. > > > > > > So this is something we've debated a few times in the past. > > > There is a fairly strong argument for output devices that the range > is > > > a characteristic of the circuit. At the very least it makes sense to > > > restrict it in DT even if we allow safe forms of tweaking in the > driver. > > > For an initial driver, I'd just have it in DT. > > > > > > > No complaints against that and makes things way simpler to handle. > Great. > > > > - Nuno Sá > > > So conclusions.. Hmm. Not strong ones yet, but for dither mode at > least > I think you want to link particular channels to a TGPx choice > > out_voltage0_raw > out_voltage0_raw_available ( nice to have on DACs) I guess here you mean 'IIO_AVAIL_RANGE'? > out_voltage0_scale > out_voltage0_dither_raw > out_voltage0_dither_raw_available > out_voltage0_dither_frequency > out_voltage0_dither_frequency_available > out_voltage0_dither_phase > out_voltage0_dither_phase_available > Toggle mode is less clear to me but symbol approach plus TGPx in DT > maybe works > You could allow for software override to set the symbol. Interface to > unset > it being to write an empty string to _symbol. Maybe leave that for > now. > > out_voltage0_raw0 > out_voltage0_raw1 > out_voltage0_scale > out_voltage0_symbol Well, in short, I do agree with this ABI. And actually, for toggle mode, I think this is more or less what we will have. For dither/default mode, there's still the questions I raised above... Maybe, at the end, we will end up with 3 different ABI's... I would only add this to the ABI: * out_voltage0_dither_en * out_voltage0_toggle_en Because if someone wants to change, let's say the dither frequency, the best way to update things is to first disable dithering, update all the stuff, and then enable it again... - Nuno Sá
> -----Original Message----- > From: Sa, Nuno <Nuno.Sa@analog.com> > Sent: Tuesday, November 30, 2021 3:43 PM > To: Jonathan Cameron <jic23@kernel.org> > Cc: linux-iio@vger.kernel.org > Subject: RE: [RFC PATCH 0/1] LTC2688 support > > [External] > > > > > -----Original Message----- > > From: Jonathan Cameron <jic23@kernel.org> > > Sent: Sunday, November 21, 2021 1:18 PM > > To: Sa, Nuno <Nuno.Sa@analog.com> > > Cc: linux-iio@vger.kernel.org > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > [External] > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > Hi Jonathan, > > > > > > Thanks for your inputs... > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > Cc: linux-iio@vger.kernel.org > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > [External] > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > Hi Nuno, > > > > > > > > > The reason why this is a RFC is because I'm still waiting for > proper > > HW > > > > > to test this thing. The reason why I'm sending this already is > > because > > > > > there's some non usual features which might require extra ABI. > > > > Hence, > > > > > while waiting I thought we could already speed up the process > in > > > > regards > > > > > with the ABI. > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really to > review > > it. > > > > > Naturally, if someone already wants to give some feedback, > > that's > > > > very > > > > > much appreciated :) > > > > > > > > > > > > > > Now, there are three main interfaces depending on the > channel > > > > mode: > > > > > 1) default (no new ABI) > > > > > 2) toggle mode > > > > > 3) dither mode > > > > > > > > > > The channel mode will be a devicetree property as it does not > > really > > > > > make much sense to change between modes at runtime even > > more > > > > because the > > > > > piece of HW we might want to control with a channel might be > > > > different > > > > > depending on the selected mode (I'm fairly sure on this > between > > > > toggle > > > > > and other modes but not so sure between dither and default > > mode). > > > > > > > > I agree on toggle vs dither definitely being different, but normal > > you > > > > could implement either as software toggle, or dither with a 0 > > > > magnitude > > > > sine wave. So might not be worth implementing default mode at > > all. > > > > No harm in doing so though if there are advantages to having it. > > > > > > My feeling is that we could probably have dither as the "default > > mode". > > > More on this below... > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > * Toggle operation enables fast switching of a DAC output > > between > > > > two > > > > > different DAC codes without any SPI transaction. Two codes are > > set > > > > in > > > > > input_a and input_b and then the output switches according to > > an > > > > input > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > out_voltageY_input_register > > > > > - selects between input_a and input_b. After selecting one > > register, > > > > we > > > > > can write the dac code in out_voltageY_raw. > > > > > out_voltageY_toggle_en > > > > > - Disable/Enable toggle mode. The reason why I think this one > is > > > > > important is because if we wanna change the 2 codes, we > > should > > > > first > > > > > disable this, set the codes and only then enable the mode > > back... > > > > > As I'm writing this, It kind of came to me that we can probably > > > > > achieve this with out_voltageY_powerdown attr (maybe > takes a > > bit > > > > more > > > > > time to see the outputs but...) > > > > > > > > Hmm. These corner cases always take a bit of figuring out. What > > you > > > > have > > > > here is a bit 'device specific' for my liking. > > > > > > > > So there is precedence for ABI in this area, on the frequency > > devices > > > > but only > > > > for devices we still haven't moved out of staging. For those we > > > > needed a means > > > > to define selectable phases for PSK - where the selection was > > either > > > > software or, > > > > much like here, a selection pin. > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > so I guess the equivalent here would be > > > > out_voltageY_raw0 > > > > out_voltageY_raw1 > > > > and the selection would be via something like > > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > > relevant if you have the software toggle. Any enable needed for > > > > setting > > > > can be done as part of the write sequence for the raw0 / raw1 > and > > > > should > > > > ideally not be exposed to userspace (controls that require > manual > > > > sequencing > > > > tend to be hard to use / document). > > > > > > Yeah, I thought about that. I was even thinking in having something > > like > > > *_amplitude for dither mode. In some cases, where we might be > left > > > in some non obvious state (eg: moved the select register to input b > > and > > > then we failed to set the code;), I prefer to leave things as flexible > as > > > possible for userspace. But I agree it adds up more complexity and > in > > > this case, I can just always go to 'input_a' when writing 'raw0'... > > > > > > > However, I'm not 100% sure it really maps to this case. What do > > you > > > > think? > > > > > > I think it can work. Though out_voltageY_symbol probably needs to > > be > > > shared by type to be coherent with what we might have with > TGPx. > > > > That's fine. > > > > > Note the sw_toggle register has a bit mask of the channels we > want > > to > > > toggle which means we can toggle multiple channels at the same > > time. > > > > Using that wired up to buffer mode might make sense. You'd > provide > > multiple > > buffers and allow channels to be selected into one of them at a time. > > Each > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > The same could be true for the software toggle. It'll get a bit fiddly > > though. > > > > Perhaps this is an advanced feature to think about later... > > > > > It works the same with TGPx if you map multiple channels to the > > same > > > pin. > > > > > > There's also the question on how to handle this if a TGPx is > provided? > > > I guess it will just override the pin... But most likely having them > both > > > at the same time will lead to non desired results (unless we have a > > > way to gate/ungate the clocks)... > > I don't follow this bit. You mean TGPx and software toggle. As far as I > > can > > tell it's an either/or thing per channel. > > > > Here I meant that if we have a TGPx pin bundled to some channel(s) > we > do not want to also dance with the sw_toggle bit of that channel. Just a note on this. After starting my tests with the device, I can actually say that if we have a TGPx set in the channel settings register, the device will pretty much ignore the sw_toggle settings for that channel. I could see that the output voltage was not toggling at all. As soon as I removed the TGPx setting, then dancing with the sw_toggle started to work. So, for the HW this is not really an issue as it just ignores the sw_toggle. On a SW perspective, I'm still not sure if I just ignore this and write whatever the user sets or if I return some error code in the case a user tries to toggle a channel with a binded TGPx. The first one is appealing as it makes the code much simpler while OTHO it might make sense to be verbose here otherwise the user might think something is happening when it isn't... Anyways, I would argue that if someone has a pin wired, it's highly unlikely that he cares about sw_toggling... - Nuno Sá
On Tue, 30 Nov 2021 14:43:25 +0000 "Sa, Nuno" <Nuno.Sa@analog.com> wrote: Hi Nuno Hopefully I've not lost the plot on this! > > -----Original Message----- > > From: Jonathan Cameron <jic23@kernel.org> > > Sent: Sunday, November 21, 2021 1:18 PM > > To: Sa, Nuno <Nuno.Sa@analog.com> > > Cc: linux-iio@vger.kernel.org > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > [External] > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > Hi Jonathan, > > > > > > Thanks for your inputs... > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > Cc: linux-iio@vger.kernel.org > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > [External] > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > Hi Nuno, > > > > > > > > > The reason why this is a RFC is because I'm still waiting for proper > > HW > > > > > to test this thing. The reason why I'm sending this already is > > because > > > > > there's some non usual features which might require extra ABI. > > > > Hence, > > > > > while waiting I thought we could already speed up the process in > > > > regards > > > > > with the ABI. > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really to review > > it. > > > > > Naturally, if someone already wants to give some feedback, > > that's > > > > very > > > > > much appreciated :) > > > > > > > > > > > > > > Now, there are three main interfaces depending on the channel > > > > mode: > > > > > 1) default (no new ABI) > > > > > 2) toggle mode > > > > > 3) dither mode > > > > > > > > > > The channel mode will be a devicetree property as it does not > > really > > > > > make much sense to change between modes at runtime even > > more > > > > because the > > > > > piece of HW we might want to control with a channel might be > > > > different > > > > > depending on the selected mode (I'm fairly sure on this between > > > > toggle > > > > > and other modes but not so sure between dither and default > > mode). > > > > > > > > I agree on toggle vs dither definitely being different, but normal > > you > > > > could implement either as software toggle, or dither with a 0 > > > > magnitude > > > > sine wave. So might not be worth implementing default mode at > > all. > > > > No harm in doing so though if there are advantages to having it. > > > > > > My feeling is that we could probably have dither as the "default > > mode". > > > More on this below... > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > * Toggle operation enables fast switching of a DAC output > > between > > > > two > > > > > different DAC codes without any SPI transaction. Two codes are > > set > > > > in > > > > > input_a and input_b and then the output switches according to > > an > > > > input > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > out_voltageY_input_register > > > > > - selects between input_a and input_b. After selecting one > > register, > > > > we > > > > > can write the dac code in out_voltageY_raw. > > > > > out_voltageY_toggle_en > > > > > - Disable/Enable toggle mode. The reason why I think this one is > > > > > important is because if we wanna change the 2 codes, we > > should > > > > first > > > > > disable this, set the codes and only then enable the mode > > back... > > > > > As I'm writing this, It kind of came to me that we can probably > > > > > achieve this with out_voltageY_powerdown attr (maybe takes a > > bit > > > > more > > > > > time to see the outputs but...) > > > > > > > > Hmm. These corner cases always take a bit of figuring out. What > > you > > > > have > > > > here is a bit 'device specific' for my liking. > > > > > > > > So there is precedence for ABI in this area, on the frequency > > devices > > > > but only > > > > for devices we still haven't moved out of staging. For those we > > > > needed a means > > > > to define selectable phases for PSK - where the selection was > > either > > > > software or, > > > > much like here, a selection pin. > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > so I guess the equivalent here would be > > > > out_voltageY_raw0 > > > > out_voltageY_raw1 > > > > and the selection would be via something like > > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > > relevant if you have the software toggle. Any enable needed for > > > > setting > > > > can be done as part of the write sequence for the raw0 / raw1 and > > > > should > > > > ideally not be exposed to userspace (controls that require manual > > > > sequencing > > > > tend to be hard to use / document). > > > > > > Yeah, I thought about that. I was even thinking in having something > > like > > > *_amplitude for dither mode. In some cases, where we might be left > > > in some non obvious state (eg: moved the select register to input b > > and > > > then we failed to set the code;), I prefer to leave things as flexible as > > > possible for userspace. But I agree it adds up more complexity and in > > > this case, I can just always go to 'input_a' when writing 'raw0'... > > > > > > > However, I'm not 100% sure it really maps to this case. What do > > you > > > > think? > > > > > > I think it can work. Though out_voltageY_symbol probably needs to > > be > > > shared by type to be coherent with what we might have with TGPx. > > > > That's fine. > > > > > Note the sw_toggle register has a bit mask of the channels we want > > to > > > toggle which means we can toggle multiple channels at the same > > time. > > > > Using that wired up to buffer mode might make sense. You'd provide > > multiple > > buffers and allow channels to be selected into one of them at a time. > > Each > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > The same could be true for the software toggle. It'll get a bit fiddly > > though. > > > > Perhaps this is an advanced feature to think about later... > > > > > It works the same with TGPx if you map multiple channels to the > > same > > > pin. > > > > > > There's also the question on how to handle this if a TGPx is provided? > > > I guess it will just override the pin... But most likely having them both > > > at the same time will lead to non desired results (unless we have a > > > way to gate/ungate the clocks)... > > I don't follow this bit. You mean TGPx and software toggle. As far as I > > can > > tell it's an either/or thing per channel. > > > > Here I meant that if we have a TGPx pin bundled to some channel(s) we > do not want to also dance with the sw_toggle bit of that channel. Ultimately, > that's on the user responsibility but we could also add some guards I guess. > I'm not sure if it's an either/or thing per channel... IIUC, we spoke about > making dither and default mode the same. That might complicate things a bit > as: > > 1) We should not force a user to specify a TGPx pin for those channels (since > it can also work with dithering disabled). > 2) Because of 1), we should also support sw_toggle for these channels since > someone might want to enable dither mode (at runtime) and the TGPx pin was > not given. Hence, we need to have a way to update the DAC using the sw_toggle. > > Did I understood things wrong? One thing that comes to my mind, is to return > error (eg: EPERM or ENOTSUPP) if someone tries to enable dither mode and > no TGPx pin was selected for that channel? Hence, we do not need to add > the sw_toggle ABI (out_voltage_symbol) for the default/dither mode. Or > maybe even better, we just expose the dither ABI if a TGPx pin is given over > dt (I try to explain the toggle/dither modes below; that might help you in > understanding my reasoning here)? > > Alternatively, we just keep the approach I have in this RFC and we keep the > 3 different modes (being mode a dt property; in the current state I'm using > a boolean to say a channel Is in toggle mode)... Maybe with the difference > that we allow sw_toggle for toggle enabled channels. The corner I'm not clear on is what we do if for example all TGPx pins are specified in DT. Is the mapping from channel to TGPx things in toggle mode always a function of the external circuit or do we want to make it runtime controllable? I'm absolutely fine if we just make it a dt property - particularly as those TGPx pins may well not be visible to the host processor. We probably do want to provide some options in dt for what they might be connnected to on the host. I'm guessing potentially a gpio, or a clk? You could also wire them to a non general purpose output pin - but that would be really hard to describe in a generic fashion. > > > > > > > > I'm not sure if whether a channel is in toggle mode is a circuit thing > > or > > > > not.. > > > > (and hence DT or userspace control?) > > > > > > The only reason I can think off to have it as DT is that toggle mode > > seems > > > to be for more specific use cases so I guess the HW we want to > > control ( > > > and connect to a toggle enabled channel) will be different. > > > > > > I'm also not seeing an use case for ping ponging between the modes > > mostly > > > because of the above... > > > > Only use I can see is to reduce traffic if you happen to be switching > > between > > two sets of DAC outputs repeatedly. If there wasn't an LDAC pin I'd > > suspect > > this was there to enable simultaneous updates but we have that > > anyway. > > Maybe if the LDAC isn't wired this could be used to provide similar > > functionality? If that's the case, we could just leave it as a possible > > TODO if anyone wants it in future... > > I think you could use the TGPx to provide controlled switching of > > sets of channels. Maybe that's something useful? > > Hmm, I think LDAC is something else. The LDAC pin updates all 16 channels > with the value of the input register (which I assume is INPUT_A) independent > of them being in dither/toggle mode. Honestly, I'm not even sure of how > thing would work if someone plays with LDAC + channels in dither/toggle > mode. I think extra care would be needed... My guess was as that in toggle mode at least, LDAC would update the DACs to reflect the 'current' toggle registers, but I'm not totally sure. > > So, TGPx pins are indeed used to control set of channels. But note that these > pins (as sw_toggle) are only meaningful if the channel is in dither or toggle > mode (the channel bit in the toggle/dither enable register has to be set): Agreed, though note that we could ensure we always were in one of these modes if it made sense from software point of view. > > * In toggle mode we have two set of input registers: INPUT_A and INPUT_B > and we toggle between these two values. If we wire a TGPx pin and bundle > it to a toggle enabled channel, when the input signal is high, we output INPUT_A > and INPUT_B when the signal is low. We can mimic the same behavior by writing > 1/0 to the sw_toggle register. There are different ways you could use this facility if you assume the TGPx pins are wired to the host processor rather than something out of our control. You could use it for double buffering for example - so update INPUT_B, then toggle, update INPUT_A then toggle etc. Or you could assume it's for mass mode switching - so there are only two values that will ever be set and these reflect something in the external circuits. We might not even have software control / visibility of which state is active. > * In dither mode, things are slightly different as INPUT_B is the value for the > sinusoidal amplitude. And if we have an external signal on a TGPx pin, the dac > channel is updated on the rising edge of the signal. Again, we can mimic the same > behavior with the sw_toggle register. > > So, for dither mode, I'm not really seeing why someone would want to use the > sw_toggle. Even for toggle mode, I have my doubts but I can more easily see it. Does seem unlikely for dither mode as you'd need a huge amount of bus traffic to basically provide a bad clock signal. Toggle I can also sort of see being useful with sw_toggle - but suspect real usecase for that is the one where the host processor isn't controlling the toggle.. > > > > > > > > Can see that even in a case where you did want to use external > > > > controls to > > > > pick the values, you might also want to override from software... > > > > Given there is a software toggle I guess we can use that as > > override. > > > > Actually that raises the question of what the point in having normal > > > > mode is? > > > > Can we just implement that as a software toggle toggle mode? One > > > > less thing to > > > > worry about if we can. > > > > > > I did thought about the sw_toggle thing (it's something that is only > > valid > > > for channels in dither/toggle mode). My reasoning was that either > > > > > > 1) I did not supported it and made the TGPx selection mandatory (in > > case > > > dither/toggle mode enabled) or > > > 2) I did support it and hence the pins are not really mandatory. > > > > > > I went with 1) because, honestly, I'm not seeing the point of having > > these > > > modes and use sw toggle (at least on a production system). > > However, if we > > > want to get rid of the default mode and have it as the dither mode, I > > agree > > > we need sw_toggle because If someone just wants to use the > > channel > > > without any dithering, we can't have an hard requirement to provide > > a > > > external TGPx. Moreover, if the default channel will be a dither > > capable > > > one, we need to provide full functionality and hence, sw_toggle. > > > > > > As I stated before, I'm just not sure on how to handle things if a TGPx > > is > > > also provided. Maybe they should be mutual exclusive? I mean, if > > someone > > > tries to toggle a channel with a mapped TGPx we return some error > > code? > > > > Given the mapping of TGPx to channel is a software control I think > > ultimately > > you'd want to expose that - one way I can think of doing that is via > > the buffer interface. > > > > 4x buffers. One of each TGP0,1,2 and SW toggle. Enable the channels > > you > > want for a given 'buffer' and then they will switch together based on > > the > > data in the buffer. If the buffer has a series of toggling values then > > it's simple - if not then after each toggle the buffer would need to > > preload > > the next value. The snag there is that you'd need to know a toggle > > occurred > > and if the toggle pins are wired to somewhere other than our host I'm > > not sure > > how you would know that in general? (could wire the same TGPx signal > > to an > > interrupt on the host controller but seems unlikely). > > Honestly I think that we would be probably over engineering things with > this even though I get your point. OTOH, as you said, the triggering would > be very hacky to handle and that might already tell us something :) It may well make sense to only implement a subset but it is often useful to walk through what a more sophisticated feature set might look like as then we don't accidentally rule it out. > > > Whether software toggle is worth bothering when we have LDAC to > > control > > simultaneous DAC updates isn't clear to me. I guess it's fewer writes > > Hopefully I could make it clear that sw_toggle is something else than LDAC :) > > > if we happen to be cycling between values. Perhaps you are right and > > that > > feature is just for debug. > > > > > > > > > There is also the question of whether selection of which toggle pin > > is > > > > used > > > > should be a dt thing or a userspace control... > > > > > > Well, this definitely means some HW wiring to have the external > > signals and > > > I'm not sure if there's any added valuable in being able to change the > > > external signal at runtime? > > > > Whilst I can conjecture reasons to do this, you may well be right - real > > usecases will know which signal groups they want to control together. > > > > > > > > > > > > > > > dither mode special ABI: > > > > > > > > > > * Dither operation adds a small sinusoidal wave to the digital DAC > > > > > signal path. Dithering is a signal processing technique that > > involves > > > > > the injection of ac noise to the signal path to reduce system > > > > > nonlinearities. > > > > > > > > > > > > > This is a complex feature to describe as (if I read it correctly) we > > have > > > > a dither clocked from an external pin, or in theory from software. > > That > > > > clock > > > > frequency must match the dither. Realistically that means it is a > > clock > > > > in our control or we have to match the period below to the > > frequency > > > > of that > > > > clock. > > > > > > Yeah, the frequency of the dither signal is fsig = fclk / N, where N can > > only > > > be: [4 8 16 32 64]. So, we kind of just have these available options for > > the > > > signal frequency and fclk is something we can control and know > > (assuming > > > we have TGPx mapping which I'm bundling with a clk). > > > > > > The only quirk with having this with frequency rather than raw N is > > > to handle the sw_toggle where we have no idea about fclk? We > > could also > > > think of this attr as some kind of decimation... > > > > Does seems unlikely anyone would use dither with a sw toggle. > > Perhaps best plan here is to not support that combination. > > Agree... But there are some subtleties that we need to settle > about the channel default mode as I raised in my previous comments. > > > As to the clock, these are about controlling a sine wave frequency. I'm > > not sure > > decimation fits as a model. (figure 19) > > > > Given you know the input clock, perhaps present this as something like > > out_voltage0_dither_frequency > > > > I don't thing dithers are always this simple, so probably want to be > > specific its > > a sine wave so maybe we need > > out_voltage0_dither_type 'sine' > > > > We used to have some DDS chips in staging but looks like they all got > > dropped due > > to end of time Those had various waveforms and IIRC all we came up > > with was > > descriptive terms + frequencies and magnitudes. > > > > > > > > > > > > out_voltage0_dither_en > > > > > - Same as in toggle mode. > > > > > out_voltage0_dither_period > > > > > out_voltage0_dither_phase > > > > > - Period and phase of the signal. Only some values are valid so > > > > there's > > > > > also *_available files for these. I'm not sure if we can use the > > more > > > > > generic IIO_CHAN_INFO_PHASE and > > IIO_CHAN_INFO_FREQUENCY > > > > here as these > > > > > parameters don't really apply to the channel output signal.. > > > > > > > > Possibly not helpful to do so, but you could describe the channel as > > an > > > > out_altvoltage channel that happens to have a significant offset > > (the > > > > DC > > > > level) and phase, frequency etc as for a normal altvoltage channel. > > > > That would hide the intention here though so perhaps not a good > > plan > > > > even if it ensures we end up with standard ABI. > > > > > > I think altvoltage might not be optimal here because the phase and > > frequency > > > are really not characteristics of the output signal of the channel. > > > > Well they kind of are if you set the magnitude high enough - but I get > > your > > point. That's not how they are intended to be used. > > > > > > > > > > out_voltage0_input_register > > > > > - Same as in toggle mode. However in this mode the code set in > > the > > > > > input_b register has a special meaning. It's the amplitude of the > > > > > dither signal. > > > > Don't do that - provide a direct attribute representing the value of > > > > register_b and when it is written implicitly switch to the right > > register. > > > > Any ABI that requires a sequence of events is hard to use. > > > > > > I guess we can just use the same raw1 attr here? Even though, in > > dither > > > mode this has special meaning (it is the amplitude)... > > > > I was thinking toggle mode here. This interface doesn't work for dither. > > in that case there is just > > out_voltage0_raw for the DC part and > > out_voltage0_dither_raw for the dither amplitude. Assumption being > > same scaling > > as I don't really want to support multiple scale factors if we can avoid it. > > I'm fairly sure it is the same scaling.... As long as it's a simple factor, just hit it with a 'small adjusting tool' until it does have the same scaling. We do that in a few similar cases IIRC as sometimes things like this dither input have lower resolution. If it's the same scaling then you won't have to hit it at all ;) > > > > > > > > > > > > > > > > > > > > > > One special mention to the dac scale. In this part this is something > > > > > that can be purely controlled by SW so that I'm allowing > > userspace to > > > > > change it rather then having it in dts. The available scales are: > > > > > > > > > > * [0 5V] -> offset 0 > > > > > * [0 10V] -> offset 0 > > > > > * [-5 5V] -> offset -32678 > > > > > * [-10 10V] -> offset -32768 > > > > > * [-15 15V] -> offset -32768 > > > > > > > > > > With the above, we also need to have the offset configurable > > and > > > > right > > > > > now I'm going to some trouble to make sure the scale + offset is > > > > > something valid. Honestly, I think I'm overdoing it because things > > can > > > > > still go wrong with [0 10V] and [-5 5V] as the scales are the same > > > > > here. Furthermore, there's no real arm that can be done to the > > HW. > > > > Is > > > > > just that the readings won't match with what someone might be > > > > expecting. > > > > > My plan is to just remove those checks and assume is up to > > > > userspace to > > > > > make it right and not have [-10 10V] scale with 0 offset for > > example. > > > > > > > > So this is something we've debated a few times in the past. > > > > There is a fairly strong argument for output devices that the range > > is > > > > a characteristic of the circuit. At the very least it makes sense to > > > > restrict it in DT even if we allow safe forms of tweaking in the > > driver. > > > > For an initial driver, I'd just have it in DT. > > > > > > > > > > No complaints against that and makes things way simpler to handle. > > Great. > > > > > > - Nuno Sá > > > > > So conclusions.. Hmm. Not strong ones yet, but for dither mode at > > least > > I think you want to link particular channels to a TGPx choice > > > > out_voltage0_raw > > out_voltage0_raw_available ( nice to have on DACs) > > I guess here you mean 'IIO_AVAIL_RANGE'? No, I mean providing the read_avail() callback and setting BIT(IIO_INFO_RAW) in info_mask_separate_available That's how we provide range for a channel except in some unusual corner cases and the internal interface for that is used when a DAC is being used via the consumer interface (so some other driver wants to set it's output). > > > out_voltage0_scale > > out_voltage0_dither_raw > > out_voltage0_dither_raw_available > > out_voltage0_dither_frequency > > out_voltage0_dither_frequency_available > > out_voltage0_dither_phase > > out_voltage0_dither_phase_available > > > Toggle mode is less clear to me but symbol approach plus TGPx in DT > > maybe works > > You could allow for software override to set the symbol. Interface to > > unset > > it being to write an empty string to _symbol. Maybe leave that for > > now. > > > > out_voltage0_raw0 > > out_voltage0_raw1 > > out_voltage0_scale > > out_voltage0_symbol > > Well, in short, I do agree with this ABI. And actually, for toggle mode, I think > this is more or less what we will have. For dither/default mode, there's still > the questions I raised above... Maybe, at the end, we will end up with 3 different > ABI's... Certainly possible. Nice to avoid if we can, but not if it means stretching things too far. > > I would only add this to the ABI: > * out_voltage0_dither_en > * out_voltage0_toggle_en > > Because if someone wants to change, let's say the dither frequency, the best way > to update things is to first disable dithering, update all the stuff, and then enable > it again... I'll go with 'maybe' for these. The use for changing things doesn't make sense to me unless we have multiple things to change at once. If it's just the frequency it would be more intuitive to have a write to that attribute do the disable, set value and enable dithering again without needing to do a dance with the interface. I'm not sure when updating needs to be done atomically across the various variables (so would need to be done under a single disable / enable sequence. > > - Nuno Sá
On Thu, 2 Dec 2021 15:37:40 +0000 "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > -----Original Message----- > > From: Sa, Nuno <Nuno.Sa@analog.com> > > Sent: Tuesday, November 30, 2021 3:43 PM > > To: Jonathan Cameron <jic23@kernel.org> > > Cc: linux-iio@vger.kernel.org > > Subject: RE: [RFC PATCH 0/1] LTC2688 support > > > > [External] > > > > > > > > > -----Original Message----- > > > From: Jonathan Cameron <jic23@kernel.org> > > > Sent: Sunday, November 21, 2021 1:18 PM > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > Cc: linux-iio@vger.kernel.org > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > [External] > > > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > > Hi Jonathan, > > > > > > > > Thanks for your inputs... > > > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > Cc: linux-iio@vger.kernel.org > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > [External] > > > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > > > Hi Nuno, > > > > > > > > > > > The reason why this is a RFC is because I'm still waiting for > > proper > > > HW > > > > > > to test this thing. The reason why I'm sending this already is > > > because > > > > > > there's some non usual features which might require extra ABI. > > > > > Hence, > > > > > > while waiting I thought we could already speed up the process > > in > > > > > regards > > > > > > with the ABI. > > > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really to > > review > > > it. > > > > > > Naturally, if someone already wants to give some feedback, > > > that's > > > > > very > > > > > > much appreciated :) > > > > > > > > > > > > > > > > > Now, there are three main interfaces depending on the > > channel > > > > > mode: > > > > > > 1) default (no new ABI) > > > > > > 2) toggle mode > > > > > > 3) dither mode > > > > > > > > > > > > The channel mode will be a devicetree property as it does not > > > really > > > > > > make much sense to change between modes at runtime even > > > more > > > > > because the > > > > > > piece of HW we might want to control with a channel might be > > > > > different > > > > > > depending on the selected mode (I'm fairly sure on this > > between > > > > > toggle > > > > > > and other modes but not so sure between dither and default > > > mode). > > > > > > > > > > I agree on toggle vs dither definitely being different, but normal > > > you > > > > > could implement either as software toggle, or dither with a 0 > > > > > magnitude > > > > > sine wave. So might not be worth implementing default mode at > > > all. > > > > > No harm in doing so though if there are advantages to having it. > > > > > > > > My feeling is that we could probably have dither as the "default > > > mode". > > > > More on this below... > > > > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > > > * Toggle operation enables fast switching of a DAC output > > > between > > > > > two > > > > > > different DAC codes without any SPI transaction. Two codes are > > > set > > > > > in > > > > > > input_a and input_b and then the output switches according to > > > an > > > > > input > > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > > > out_voltageY_input_register > > > > > > - selects between input_a and input_b. After selecting one > > > register, > > > > > we > > > > > > can write the dac code in out_voltageY_raw. > > > > > > out_voltageY_toggle_en > > > > > > - Disable/Enable toggle mode. The reason why I think this one > > is > > > > > > important is because if we wanna change the 2 codes, we > > > should > > > > > first > > > > > > disable this, set the codes and only then enable the mode > > > back... > > > > > > As I'm writing this, It kind of came to me that we can probably > > > > > > achieve this with out_voltageY_powerdown attr (maybe > > takes a > > > bit > > > > > more > > > > > > time to see the outputs but...) > > > > > > > > > > Hmm. These corner cases always take a bit of figuring out. What > > > you > > > > > have > > > > > here is a bit 'device specific' for my liking. > > > > > > > > > > So there is precedence for ABI in this area, on the frequency > > > devices > > > > > but only > > > > > for devices we still haven't moved out of staging. For those we > > > > > needed a means > > > > > to define selectable phases for PSK - where the selection was > > > either > > > > > software or, > > > > > much like here, a selection pin. > > > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > > > so I guess the equivalent here would be > > > > > out_voltageY_raw0 > > > > > out_voltageY_raw1 > > > > > and the selection would be via something like > > > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > > > relevant if you have the software toggle. Any enable needed for > > > > > setting > > > > > can be done as part of the write sequence for the raw0 / raw1 > > and > > > > > should > > > > > ideally not be exposed to userspace (controls that require > > manual > > > > > sequencing > > > > > tend to be hard to use / document). > > > > > > > > Yeah, I thought about that. I was even thinking in having something > > > like > > > > *_amplitude for dither mode. In some cases, where we might be > > left > > > > in some non obvious state (eg: moved the select register to input b > > > and > > > > then we failed to set the code;), I prefer to leave things as flexible > > as > > > > possible for userspace. But I agree it adds up more complexity and > > in > > > > this case, I can just always go to 'input_a' when writing 'raw0'... > > > > > > > > > However, I'm not 100% sure it really maps to this case. What do > > > you > > > > > think? > > > > > > > > I think it can work. Though out_voltageY_symbol probably needs to > > > be > > > > shared by type to be coherent with what we might have with > > TGPx. > > > > > > That's fine. > > > > > > > Note the sw_toggle register has a bit mask of the channels we > > want > > > to > > > > toggle which means we can toggle multiple channels at the same > > > time. > > > > > > Using that wired up to buffer mode might make sense. You'd > > provide > > > multiple > > > buffers and allow channels to be selected into one of them at a time. > > > Each > > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > > > The same could be true for the software toggle. It'll get a bit fiddly > > > though. > > > > > > Perhaps this is an advanced feature to think about later... > > > > > > > It works the same with TGPx if you map multiple channels to the > > > same > > > > pin. > > > > > > > > There's also the question on how to handle this if a TGPx is > > provided? > > > > I guess it will just override the pin... But most likely having them > > both > > > > at the same time will lead to non desired results (unless we have a > > > > way to gate/ungate the clocks)... > > > I don't follow this bit. You mean TGPx and software toggle. As far as I > > > can > > > tell it's an either/or thing per channel. > > > > > > > Here I meant that if we have a TGPx pin bundled to some channel(s) > > we > > do not want to also dance with the sw_toggle bit of that channel. > > Just a note on this. After starting my tests with the device, I can actually > say that if we have a TGPx set in the channel settings register, the device > will pretty much ignore the sw_toggle settings for that channel. I could > see that the output voltage was not toggling at all. As soon as I removed > the TGPx setting, then dancing with the sw_toggle started to work. So, for > the HW this is not really an issue as it just ignores the sw_toggle. On a SW > perspective, I'm still not sure if I just ignore this and write whatever the > user sets or if I return some error code in the case a user tries to toggle > a channel with a binded TGPx. The first one is appealing as it makes the > code much simpler while OTHO it might make sense to be verbose here > otherwise the user might think something is happening when it isn't... If we are in a static configuration (see below) then just don't expose the software toggle control. Not having a big red button to press is the best way to tell userspace to not press the big red button... > > Anyways, I would argue that if someone has a pin wired, it's highly unlikely > that he cares about sw_toggling... I'd agree if there was one to one mapping from TGPx to channel. Given it's highly configurable, they 'might' want to set the mapping differently at runtime. I'm fine if we don't support that option until someone asks though. Jonathan > > - Nuno Sá >
> -----Original Message----- > From: Jonathan Cameron <jic23@kernel.org> > Sent: Sunday, December 5, 2021 7:01 PM > To: Sa, Nuno <Nuno.Sa@analog.com> > Cc: linux-iio@vger.kernel.org > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > [External] > > On Tue, 30 Nov 2021 14:43:25 +0000 > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > Hi Nuno > > Hopefully I've not lost the plot on this! Not really. I had some days off so this was also set on hold from my side. > > > -----Original Message----- > > > From: Jonathan Cameron <jic23@kernel.org> > > > Sent: Sunday, November 21, 2021 1:18 PM > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > Cc: linux-iio@vger.kernel.org > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > [External] > > > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > > Hi Jonathan, > > > > > > > > Thanks for your inputs... > > > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > Cc: linux-iio@vger.kernel.org > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > [External] > > > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > > > Hi Nuno, > > > > > > > > > > > The reason why this is a RFC is because I'm still waiting for > proper > > > HW > > > > > > to test this thing. The reason why I'm sending this already is > > > because > > > > > > there's some non usual features which might require extra > ABI. > > > > > Hence, > > > > > > while waiting I thought we could already speed up the > process in > > > > > regards > > > > > > with the ABI. > > > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really to > review > > > it. > > > > > > Naturally, if someone already wants to give some feedback, > > > that's > > > > > very > > > > > > much appreciated :) > > > > > > > > > > > > > > > > > Now, there are three main interfaces depending on the > channel > > > > > mode: > > > > > > 1) default (no new ABI) > > > > > > 2) toggle mode > > > > > > 3) dither mode > > > > > > > > > > > > The channel mode will be a devicetree property as it does not > > > really > > > > > > make much sense to change between modes at runtime > even > > > more > > > > > because the > > > > > > piece of HW we might want to control with a channel might > be > > > > > different > > > > > > depending on the selected mode (I'm fairly sure on this > between > > > > > toggle > > > > > > and other modes but not so sure between dither and default > > > mode). > > > > > > > > > > I agree on toggle vs dither definitely being different, but normal > > > you > > > > > could implement either as software toggle, or dither with a 0 > > > > > magnitude > > > > > sine wave. So might not be worth implementing default mode > at > > > all. > > > > > No harm in doing so though if there are advantages to having it. > > > > > > > > My feeling is that we could probably have dither as the "default > > > mode". > > > > More on this below... > > > > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > > > * Toggle operation enables fast switching of a DAC output > > > between > > > > > two > > > > > > different DAC codes without any SPI transaction. Two codes > are > > > set > > > > > in > > > > > > input_a and input_b and then the output switches according > to > > > an > > > > > input > > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > > > out_voltageY_input_register > > > > > > - selects between input_a and input_b. After selecting one > > > register, > > > > > we > > > > > > can write the dac code in out_voltageY_raw. > > > > > > out_voltageY_toggle_en > > > > > > - Disable/Enable toggle mode. The reason why I think this > one is > > > > > > important is because if we wanna change the 2 codes, we > > > should > > > > > first > > > > > > disable this, set the codes and only then enable the mode > > > back... > > > > > > As I'm writing this, It kind of came to me that we can > probably > > > > > > achieve this with out_voltageY_powerdown attr (maybe > takes a > > > bit > > > > > more > > > > > > time to see the outputs but...) > > > > > > > > > > Hmm. These corner cases always take a bit of figuring out. > What > > > you > > > > > have > > > > > here is a bit 'device specific' for my liking. > > > > > > > > > > So there is precedence for ABI in this area, on the frequency > > > devices > > > > > but only > > > > > for devices we still haven't moved out of staging. For those we > > > > > needed a means > > > > > to define selectable phases for PSK - where the selection was > > > either > > > > > software or, > > > > > much like here, a selection pin. > > > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > > > so I guess the equivalent here would be > > > > > out_voltageY_raw0 > > > > > out_voltageY_raw1 > > > > > and the selection would be via something like > > > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > > > relevant if you have the software toggle. Any enable needed > for > > > > > setting > > > > > can be done as part of the write sequence for the raw0 / raw1 > and > > > > > should > > > > > ideally not be exposed to userspace (controls that require > manual > > > > > sequencing > > > > > tend to be hard to use / document). > > > > > > > > Yeah, I thought about that. I was even thinking in having > something > > > like > > > > *_amplitude for dither mode. In some cases, where we might be > left > > > > in some non obvious state (eg: moved the select register to input > b > > > and > > > > then we failed to set the code;), I prefer to leave things as > flexible as > > > > possible for userspace. But I agree it adds up more complexity > and in > > > > this case, I can just always go to 'input_a' when writing 'raw0'... > > > > > > > > > However, I'm not 100% sure it really maps to this case. What do > > > you > > > > > think? > > > > > > > > I think it can work. Though out_voltageY_symbol probably needs > to > > > be > > > > shared by type to be coherent with what we might have with > TGPx. > > > > > > That's fine. > > > > > > > Note the sw_toggle register has a bit mask of the channels we > want > > > to > > > > toggle which means we can toggle multiple channels at the same > > > time. > > > > > > Using that wired up to buffer mode might make sense. You'd > provide > > > multiple > > > buffers and allow channels to be selected into one of them at a > time. > > > Each > > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > > > The same could be true for the software toggle. It'll get a bit fiddly > > > though. > > > > > > Perhaps this is an advanced feature to think about later... > > > > > > > It works the same with TGPx if you map multiple channels to the > > > same > > > > pin. > > > > > > > > There's also the question on how to handle this if a TGPx is > provided? > > > > I guess it will just override the pin... But most likely having them > both > > > > at the same time will lead to non desired results (unless we have > a > > > > way to gate/ungate the clocks)... > > > I don't follow this bit. You mean TGPx and software toggle. As far > as I > > > can > > > tell it's an either/or thing per channel. > > > > > > > Here I meant that if we have a TGPx pin bundled to some channel(s) > we > > do not want to also dance with the sw_toggle bit of that channel. > Ultimately, > > that's on the user responsibility but we could also add some guards I > guess. > > I'm not sure if it's an either/or thing per channel... IIUC, we spoke > about > > making dither and default mode the same. That might complicate > things a bit > > as: > > > > 1) We should not force a user to specify a TGPx pin for those > channels (since > > it can also work with dithering disabled). > > 2) Because of 1), we should also support sw_toggle for these > channels since > > someone might want to enable dither mode (at runtime) and the > TGPx pin was > > not given. Hence, we need to have a way to update the DAC using > the sw_toggle. > > > > Did I understood things wrong? One thing that comes to my mind, is > to return > > error (eg: EPERM or ENOTSUPP) if someone tries to enable dither > mode and > > no TGPx pin was selected for that channel? Hence, we do not need > to add > > the sw_toggle ABI (out_voltage_symbol) for the default/dither > mode. Or > > maybe even better, we just expose the dither ABI if a TGPx pin is > given over > > dt (I try to explain the toggle/dither modes below; that might help > you in > > understanding my reasoning here)? > > > > Alternatively, we just keep the approach I have in this RFC and we > keep the > > 3 different modes (being mode a dt property; in the current state I'm > using > > a boolean to say a channel Is in toggle mode)... Maybe with the > difference > > that we allow sw_toggle for toggle enabled channels. > > The corner I'm not clear on is what we do if for example all TGPx pins > are > specified in DT. Is the mapping from channel to TGPx things in toggle > mode > always a function of the external circuit or do we want to make it > runtime > controllable? > > I'm absolutely fine if we just make it a dt property - particularly > as those TGPx pins may well not be visible to the host processor. > > We probably do want to provide some options in dt for what they > might be > connnected to on the host. I'm guessing potentially a gpio, or a clk? For each TGPx pin (from the point you bind it to some channel), I'm actually making it mandatory to have a clock (the reasoning being, if you say some channel is controlled over TGPx [being for toggle or dither mode], you need to have some input at the pin). I might not be doing it in the way you're thinking but you can have a look in the actual series :) ... > You could also wire them to a non general purpose output pin - but > that > would be really hard to describe in a generic fashion. > > > > > > > > > > > > I'm not sure if whether a channel is in toggle mode is a circuit > thing > > > or > > > > > not.. > > > > > (and hence DT or userspace control?) > > > > > > > > The only reason I can think off to have it as DT is that toggle mode > > > seems > > > > to be for more specific use cases so I guess the HW we want to > > > control ( > > > > and connect to a toggle enabled channel) will be different. > > > > > > > > I'm also not seeing an use case for ping ponging between the > modes > > > mostly > > > > because of the above... > > > > > > Only use I can see is to reduce traffic if you happen to be switching > > > between > > > two sets of DAC outputs repeatedly. If there wasn't an LDAC pin I'd > > > suspect > > > this was there to enable simultaneous updates but we have that > > > anyway. > > > Maybe if the LDAC isn't wired this could be used to provide similar > > > functionality? If that's the case, we could just leave it as a possible > > > TODO if anyone wants it in future... > > > I think you could use the TGPx to provide controlled switching of > > > sets of channels. Maybe that's something useful? > > > > Hmm, I think LDAC is something else. The LDAC pin updates all 16 > channels > > with the value of the input register (which I assume is INPUT_A) > independent > > of them being in dither/toggle mode. Honestly, I'm not even sure of > how > > thing would work if someone plays with LDAC + channels in > dither/toggle > > mode. I think extra care would be needed... > > My guess was as that in toggle mode at least, LDAC would update the > DACs to > reflect the 'current' toggle registers, but I'm not totally sure. > > > > So, TGPx pins are indeed used to control set of channels. But note > that these > > pins (as sw_toggle) are only meaningful if the channel is in dither or > toggle > > mode (the channel bit in the toggle/dither enable register has to be > set): > > Agreed, though note that we could ensure we always were in one of > these modes > if it made sense from software point of view. Probably not because I can easily see users just wanting to have channels operating in the default mode... > > > > * In toggle mode we have two set of input registers: INPUT_A and > INPUT_B > > and we toggle between these two values. If we wire a TGPx pin and > bundle > > it to a toggle enabled channel, when the input signal is high, we > output INPUT_A > > and INPUT_B when the signal is low. We can mimic the same > behavior by writing > > 1/0 to the sw_toggle register. > > There are different ways you could use this facility if you assume the > TGPx pins > are wired to the host processor rather than something out of our > control. > > You could use it for double buffering for example - so update > INPUT_B, then toggle, > update INPUT_A then toggle etc. > Or you could assume it's for mass mode switching - so there are only > two values > that will ever be set and these reflect something in the external > circuits. We > might not even have software control / visibility of which state is > active. > > > * In dither mode, things are slightly different as INPUT_B is the value > for the > > sinusoidal amplitude. And if we have an external signal on a TGPx > pin, the dac > > channel is updated on the rising edge of the signal. Again, we can > mimic the same > > behavior with the sw_toggle register. > > > > So, for dither mode, I'm not really seeing why someone would want > to use the > > sw_toggle. Even for toggle mode, I have my doubts but I can more > easily see it. > > Does seem unlikely for dither mode as you'd need a huge amount of > bus traffic > to basically provide a bad clock signal. Toggle I can also sort of see > being useful with sw_toggle - but suspect real usecase for that is the > one > where the host processor isn't controlling the toggle.. Agreed (that's also my feeling)... > > > > > > > > > > > Can see that even in a case where you did want to use external > > > > > controls to > > > > > pick the values, you might also want to override from > software... > > > > > Given there is a software toggle I guess we can use that as > > > override. > > > > > Actually that raises the question of what the point in having > normal > > > > > mode is? > > > > > Can we just implement that as a software toggle toggle mode? > One > > > > > less thing to > > > > > worry about if we can. > > > > > > > > I did thought about the sw_toggle thing (it's something that is > only > > > valid > > > > for channels in dither/toggle mode). My reasoning was that > either > > > > > > > > 1) I did not supported it and made the TGPx selection mandatory > (in > > > case > > > > dither/toggle mode enabled) or > > > > 2) I did support it and hence the pins are not really mandatory. > > > > > > > > I went with 1) because, honestly, I'm not seeing the point of > having > > > these > > > > modes and use sw toggle (at least on a production system). > > > However, if we > > > > want to get rid of the default mode and have it as the dither > mode, I > > > agree > > > > we need sw_toggle because If someone just wants to use the > > > channel > > > > without any dithering, we can't have an hard requirement to > provide > > > a > > > > external TGPx. Moreover, if the default channel will be a dither > > > capable > > > > one, we need to provide full functionality and hence, sw_toggle. > > > > > > > > As I stated before, I'm just not sure on how to handle things if a > TGPx > > > is > > > > also provided. Maybe they should be mutual exclusive? I mean, if > > > someone > > > > tries to toggle a channel with a mapped TGPx we return some > error > > > code? > > > > > > Given the mapping of TGPx to channel is a software control I think > > > ultimately > > > you'd want to expose that - one way I can think of doing that is via > > > the buffer interface. > > > > > > 4x buffers. One of each TGP0,1,2 and SW toggle. Enable the > channels > > > you > > > want for a given 'buffer' and then they will switch together based > on > > > the > > > data in the buffer. If the buffer has a series of toggling values then > > > it's simple - if not then after each toggle the buffer would need to > > > preload > > > the next value. The snag there is that you'd need to know a toggle > > > occurred > > > and if the toggle pins are wired to somewhere other than our host > I'm > > > not sure > > > how you would know that in general? (could wire the same TGPx > signal > > > to an > > > interrupt on the host controller but seems unlikely). > > > > Honestly I think that we would be probably over engineering things > with > > this even though I get your point. OTOH, as you said, the triggering > would > > be very hacky to handle and that might already tell us something :) > > It may well make sense to only implement a subset but it is often > useful > to walk through what a more sophisticated feature set might look like > as then we don't accidentally rule it out. > > > > > > Whether software toggle is worth bothering when we have LDAC > to > > > control > > > simultaneous DAC updates isn't clear to me. I guess it's fewer > writes > > > > Hopefully I could make it clear that sw_toggle is something else than > LDAC :) > > > > > if we happen to be cycling between values. Perhaps you are right > and > > > that > > > feature is just for debug. > > > > > > > > > > > > There is also the question of whether selection of which toggle > pin > > > is > > > > > used > > > > > should be a dt thing or a userspace control... > > > > > > > > Well, this definitely means some HW wiring to have the external > > > signals and > > > > I'm not sure if there's any added valuable in being able to change > the > > > > external signal at runtime? > > > > > > Whilst I can conjecture reasons to do this, you may well be right - > real > > > usecases will know which signal groups they want to control > together. > > > > > > > > > > > > > > > > > > > dither mode special ABI: > > > > > > > > > > > > * Dither operation adds a small sinusoidal wave to the digital > DAC > > > > > > signal path. Dithering is a signal processing technique that > > > involves > > > > > > the injection of ac noise to the signal path to reduce system > > > > > > nonlinearities. > > > > > > > > > > > > > > > > This is a complex feature to describe as (if I read it correctly) we > > > have > > > > > a dither clocked from an external pin, or in theory from > software. > > > That > > > > > clock > > > > > frequency must match the dither. Realistically that means it is a > > > clock > > > > > in our control or we have to match the period below to the > > > frequency > > > > > of that > > > > > clock. > > > > > > > > Yeah, the frequency of the dither signal is fsig = fclk / N, where N > can > > > only > > > > be: [4 8 16 32 64]. So, we kind of just have these available options > for > > > the > > > > signal frequency and fclk is something we can control and know > > > (assuming > > > > we have TGPx mapping which I'm bundling with a clk). > > > > > > > > The only quirk with having this with frequency rather than raw N > is > > > > to handle the sw_toggle where we have no idea about fclk? We > > > could also > > > > think of this attr as some kind of decimation... > > > > > > Does seems unlikely anyone would use dither with a sw toggle. > > > Perhaps best plan here is to not support that combination. > > > > Agree... But there are some subtleties that we need to settle > > about the channel default mode as I raised in my previous > comments. > > > > > As to the clock, these are about controlling a sine wave frequency. > I'm > > > not sure > > > decimation fits as a model. (figure 19) > > > > > > Given you know the input clock, perhaps present this as something > like > > > out_voltage0_dither_frequency > > > > > > I don't thing dithers are always this simple, so probably want to be > > > specific its > > > a sine wave so maybe we need > > > out_voltage0_dither_type 'sine' > > > > > > We used to have some DDS chips in staging but looks like they all > got > > > dropped due > > > to end of time Those had various waveforms and IIRC all we came > up > > > with was > > > descriptive terms + frequencies and magnitudes. > > > > > > > > > > > > > > > > out_voltage0_dither_en > > > > > > - Same as in toggle mode. > > > > > > out_voltage0_dither_period > > > > > > out_voltage0_dither_phase > > > > > > - Period and phase of the signal. Only some values are valid > so > > > > > there's > > > > > > also *_available files for these. I'm not sure if we can use > the > > > more > > > > > > generic IIO_CHAN_INFO_PHASE and > > > IIO_CHAN_INFO_FREQUENCY > > > > > here as these > > > > > > parameters don't really apply to the channel output signal.. > > > > > > > > > > Possibly not helpful to do so, but you could describe the > channel as > > > an > > > > > out_altvoltage channel that happens to have a significant offset > > > (the > > > > > DC > > > > > level) and phase, frequency etc as for a normal altvoltage > channel. > > > > > That would hide the intention here though so perhaps not a > good > > > plan > > > > > even if it ensures we end up with standard ABI. > > > > > > > > I think altvoltage might not be optimal here because the phase > and > > > frequency > > > > are really not characteristics of the output signal of the channel. > > > > > > Well they kind of are if you set the magnitude high enough - but I > get > > > your > > > point. That's not how they are intended to be used. > > > > > > > > > > > > > out_voltage0_input_register > > > > > > - Same as in toggle mode. However in this mode the code set > in > > > the > > > > > > input_b register has a special meaning. It's the amplitude of > the > > > > > > dither signal. > > > > > Don't do that - provide a direct attribute representing the value > of > > > > > register_b and when it is written implicitly switch to the right > > > register. > > > > > Any ABI that requires a sequence of events is hard to use. > > > > > > > > I guess we can just use the same raw1 attr here? Even though, in > > > dither > > > > mode this has special meaning (it is the amplitude)... > > > > > > I was thinking toggle mode here. This interface doesn't work for > dither. > > > in that case there is just > > > out_voltage0_raw for the DC part and > > > out_voltage0_dither_raw for the dither amplitude. Assumption > being > > > same scaling > > > as I don't really want to support multiple scale factors if we can > avoid it. > > > > I'm fairly sure it is the same scaling.... > > As long as it's a simple factor, just hit it with a 'small adjusting tool' > until it does have the same scaling. We do that in a few similar cases > IIRC as sometimes things like this dither input have lower resolution. > > If it's the same scaling then you won't have to hit it at all ;) Hmm, I went to confirm this and I'm not so sure since our range here is not the full 16bits but rather 13bits (2 LSB are to be set to 0). I will have to look at this more carefully. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > One special mention to the dac scale. In this part this is > something > > > > > > that can be purely controlled by SW so that I'm allowing > > > userspace to > > > > > > change it rather then having it in dts. The available scales are: > > > > > > > > > > > > * [0 5V] -> offset 0 > > > > > > * [0 10V] -> offset 0 > > > > > > * [-5 5V] -> offset -32678 > > > > > > * [-10 10V] -> offset -32768 > > > > > > * [-15 15V] -> offset -32768 > > > > > > > > > > > > With the above, we also need to have the offset configurable > > > and > > > > > right > > > > > > now I'm going to some trouble to make sure the scale + offset > is > > > > > > something valid. Honestly, I think I'm overdoing it because > things > > > can > > > > > > still go wrong with [0 10V] and [-5 5V] as the scales are the > same > > > > > > here. Furthermore, there's no real arm that can be done to > the > > > HW. > > > > > Is > > > > > > just that the readings won't match with what someone might > be > > > > > expecting. > > > > > > My plan is to just remove those checks and assume is up to > > > > > userspace to > > > > > > make it right and not have [-10 10V] scale with 0 offset for > > > example. > > > > > > > > > > So this is something we've debated a few times in the past. > > > > > There is a fairly strong argument for output devices that the > range > > > is > > > > > a characteristic of the circuit. At the very least it makes sense to > > > > > restrict it in DT even if we allow safe forms of tweaking in the > > > driver. > > > > > For an initial driver, I'd just have it in DT. > > > > > > > > > > > > > No complaints against that and makes things way simpler to > handle. > > > Great. > > > > > > > > - Nuno Sá > > > > > > > So conclusions.. Hmm. Not strong ones yet, but for dither mode at > > > least > > > I think you want to link particular channels to a TGPx choice > > > > > > out_voltage0_raw > > > out_voltage0_raw_available ( nice to have on DACs) > > > > I guess here you mean 'IIO_AVAIL_RANGE'? > > No, I mean providing the read_avail() callback and setting > BIT(IIO_INFO_RAW) in info_mask_separate_available > > That's how we provide range for a channel except in some unusual > corner cases and the internal interface for that is used when a DAC > is being used via the consumer interface (so some other driver wants > to set it's output). Yeah, I know :). I was just meaning 'IIO_AVAIL_RANGE' over 'IIO_AVAIL_LIST'. I guess that was already obvious to you :). > > > > > out_voltage0_scale > > > out_voltage0_dither_raw > > > out_voltage0_dither_raw_available > > > out_voltage0_dither_frequency > > > out_voltage0_dither_frequency_available > > > out_voltage0_dither_phase > > > out_voltage0_dither_phase_available > > > > > Toggle mode is less clear to me but symbol approach plus TGPx in > DT > > > maybe works > > > You could allow for software override to set the symbol. Interface > to > > > unset > > > it being to write an empty string to _symbol. Maybe leave that for > > > now. > > > > > > out_voltage0_raw0 > > > out_voltage0_raw1 > > > out_voltage0_scale > > > out_voltage0_symbol > > > > Well, in short, I do agree with this ABI. And actually, for toggle mode, > I think > > this is more or less what we will have. For dither/default mode, > there's still > > the questions I raised above... Maybe, at the end, we will end up > with 3 different > > ABI's... > > Certainly possible. Nice to avoid if we can, but not if it means > stretching > things too far. > > > > > I would only add this to the ABI: > > * out_voltage0_dither_en > > * out_voltage0_toggle_en > > > > Because if someone wants to change, let's say the dither frequency, > the best way > > to update things is to first disable dithering, update all the stuff, and > then enable > > it again... > > I'll go with 'maybe' for these. The use for changing things doesn't > make sense to me > unless we have multiple things to change at once. If it's just the > frequency it > would be more intuitive to have a write to that attribute do the > disable, set value > and enable dithering again without needing to do a dance with the > interface. Yeah and that is something that can happen here (and probably the most likely situation). For dither mode, you disable it, then you might want to change all the parameters of your dither (amplitude, phase and frequency) and then enable it again. For toggle mode, this means, disabling it, updating input_a and input_b and enable it again. Anyways, I think we already have some discussion that enables me to send the first version of this and we can continue from there. If all goes well, it should be out by the end of the week. - Nuno Sá
> From: Jonathan Cameron <jic23@kernel.org> > Sent: Sunday, December 5, 2021 7:04 PM > To: Sa, Nuno <Nuno.Sa@analog.com> > Cc: linux-iio@vger.kernel.org > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > [External] > > On Thu, 2 Dec 2021 15:37:40 +0000 > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > -----Original Message----- > > > From: Sa, Nuno <Nuno.Sa@analog.com> > > > Sent: Tuesday, November 30, 2021 3:43 PM > > > To: Jonathan Cameron <jic23@kernel.org> > > > Cc: linux-iio@vger.kernel.org > > > Subject: RE: [RFC PATCH 0/1] LTC2688 support > > > > > > [External] > > > > > > > > > > > > > -----Original Message----- > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > Sent: Sunday, November 21, 2021 1:18 PM > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > Cc: linux-iio@vger.kernel.org > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > [External] > > > > > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > > > > Hi Jonathan, > > > > > > > > > > Thanks for your inputs... > > > > > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > > Cc: linux-iio@vger.kernel.org > > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > > > [External] > > > > > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > > > > > Hi Nuno, > > > > > > > > > > > > > The reason why this is a RFC is because I'm still waiting for > > > proper > > > > HW > > > > > > > to test this thing. The reason why I'm sending this already is > > > > because > > > > > > > there's some non usual features which might require extra > ABI. > > > > > > Hence, > > > > > > > while waiting I thought we could already speed up the > process > > > in > > > > > > regards > > > > > > > with the ABI. > > > > > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really to > > > review > > > > it. > > > > > > > Naturally, if someone already wants to give some feedback, > > > > that's > > > > > > very > > > > > > > much appreciated :) > > > > > > > > > > > > > > > > > > > > Now, there are three main interfaces depending on the > > > channel > > > > > > mode: > > > > > > > 1) default (no new ABI) > > > > > > > 2) toggle mode > > > > > > > 3) dither mode > > > > > > > > > > > > > > The channel mode will be a devicetree property as it does > not > > > > really > > > > > > > make much sense to change between modes at runtime > even > > > > more > > > > > > because the > > > > > > > piece of HW we might want to control with a channel might > be > > > > > > different > > > > > > > depending on the selected mode (I'm fairly sure on this > > > between > > > > > > toggle > > > > > > > and other modes but not so sure between dither and > default > > > > mode). > > > > > > > > > > > > I agree on toggle vs dither definitely being different, but > normal > > > > you > > > > > > could implement either as software toggle, or dither with a 0 > > > > > > magnitude > > > > > > sine wave. So might not be worth implementing default > mode at > > > > all. > > > > > > No harm in doing so though if there are advantages to having > it. > > > > > > > > > > My feeling is that we could probably have dither as the "default > > > > mode". > > > > > More on this below... > > > > > > > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > > > > > * Toggle operation enables fast switching of a DAC output > > > > between > > > > > > two > > > > > > > different DAC codes without any SPI transaction. Two codes > are > > > > set > > > > > > in > > > > > > > input_a and input_b and then the output switches > according to > > > > an > > > > > > input > > > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > > > > > out_voltageY_input_register > > > > > > > - selects between input_a and input_b. After selecting one > > > > register, > > > > > > we > > > > > > > can write the dac code in out_voltageY_raw. > > > > > > > out_voltageY_toggle_en > > > > > > > - Disable/Enable toggle mode. The reason why I think this > one > > > is > > > > > > > important is because if we wanna change the 2 codes, we > > > > should > > > > > > first > > > > > > > disable this, set the codes and only then enable the mode > > > > back... > > > > > > > As I'm writing this, It kind of came to me that we can > probably > > > > > > > achieve this with out_voltageY_powerdown attr (maybe > > > takes a > > > > bit > > > > > > more > > > > > > > time to see the outputs but...) > > > > > > > > > > > > Hmm. These corner cases always take a bit of figuring out. > What > > > > you > > > > > > have > > > > > > here is a bit 'device specific' for my liking. > > > > > > > > > > > > So there is precedence for ABI in this area, on the frequency > > > > devices > > > > > > but only > > > > > > for devices we still haven't moved out of staging. For those > we > > > > > > needed a means > > > > > > to define selectable phases for PSK - where the selection was > > > > either > > > > > > software or, > > > > > > much like here, a selection pin. > > > > > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > > > > > so I guess the equivalent here would be > > > > > > out_voltageY_raw0 > > > > > > out_voltageY_raw1 > > > > > > and the selection would be via something like > > > > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > > > > relevant if you have the software toggle. Any enable needed > for > > > > > > setting > > > > > > can be done as part of the write sequence for the raw0 / > raw1 > > > and > > > > > > should > > > > > > ideally not be exposed to userspace (controls that require > > > manual > > > > > > sequencing > > > > > > tend to be hard to use / document). > > > > > > > > > > Yeah, I thought about that. I was even thinking in having > something > > > > like > > > > > *_amplitude for dither mode. In some cases, where we might > be > > > left > > > > > in some non obvious state (eg: moved the select register to > input b > > > > and > > > > > then we failed to set the code;), I prefer to leave things as > flexible > > > as > > > > > possible for userspace. But I agree it adds up more complexity > and > > > in > > > > > this case, I can just always go to 'input_a' when writing 'raw0'... > > > > > > > > > > > However, I'm not 100% sure it really maps to this case. What > do > > > > you > > > > > > think? > > > > > > > > > > I think it can work. Though out_voltageY_symbol probably > needs to > > > > be > > > > > shared by type to be coherent with what we might have with > > > TGPx. > > > > > > > > That's fine. > > > > > > > > > Note the sw_toggle register has a bit mask of the channels we > > > want > > > > to > > > > > toggle which means we can toggle multiple channels at the > same > > > > time. > > > > > > > > Using that wired up to buffer mode might make sense. You'd > > > provide > > > > multiple > > > > buffers and allow channels to be selected into one of them at a > time. > > > > Each > > > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > > > > > The same could be true for the software toggle. It'll get a bit > fiddly > > > > though. > > > > > > > > Perhaps this is an advanced feature to think about later... > > > > > > > > > It works the same with TGPx if you map multiple channels to > the > > > > same > > > > > pin. > > > > > > > > > > There's also the question on how to handle this if a TGPx is > > > provided? > > > > > I guess it will just override the pin... But most likely having them > > > both > > > > > at the same time will lead to non desired results (unless we > have a > > > > > way to gate/ungate the clocks)... > > > > I don't follow this bit. You mean TGPx and software toggle. As far > as I > > > > can > > > > tell it's an either/or thing per channel. > > > > > > > > > > Here I meant that if we have a TGPx pin bundled to some > channel(s) > > > we > > > do not want to also dance with the sw_toggle bit of that channel. > > > > Just a note on this. After starting my tests with the device, I can > actually > > say that if we have a TGPx set in the channel settings register, the > device > > will pretty much ignore the sw_toggle settings for that channel. I > could > > see that the output voltage was not toggling at all. As soon as I > removed > > the TGPx setting, then dancing with the sw_toggle started to work. > So, for > > the HW this is not really an issue as it just ignores the sw_toggle. On a > SW > > perspective, I'm still not sure if I just ignore this and write whatever > the > > user sets or if I return some error code in the case a user tries to > toggle > > a channel with a binded TGPx. The first one is appealing as it makes > the > > code much simpler while OTHO it might make sense to be verbose > here > > otherwise the user might think something is happening when it > isn't... > > If we are in a static configuration (see below) then just don't expose > the > software toggle control. Not having a big red button to press is the > best way to > tell userspace to not press the big red button... Hmm, I get your point and that's valid if I have the sw_toggle as a per channel attribute. Right now, I'm doing it as shared_by_type. The reason is the sw_toggling is done by writing 1/0 in the toggle register and that register is a bitmask being the mask 16bits wide. This allows you to toggle channels at the same time in the same way you can do it if, say, you map 2,3 or more channels to the same TGPx pin. However, I'm also not happy for having this as shared_by_type attr. One of my complains is that it makes it look like a dither capable channel will also support this (and we already agreed that sw_toggle does not make sense for dither mode; so do not expose it). For instance the output of 'iio_attr' on a dither enabled channel is: ``` root@analog:~# iio_attr -c ltc2688 voltage0 dev 'ltc2688', channel 'voltage0' (output), attr 'calibbias', value '0' dev 'ltc2688', channel 'voltage0' (output), attr 'calibscale', value '0' dev 'ltc2688', channel 'voltage0' (output), attr 'dither_en', value '0' dev 'ltc2688', channel 'voltage0' (output), attr 'dither_frequency', value '32768' dev 'ltc2688', channel 'voltage0' (output), attr 'dither_frequency_available', value '32768 16384 8192 4096 2048' dev 'ltc2688', channel 'voltage0' (output), attr 'dither_phase', value '0' dev 'ltc2688', channel 'voltage0' (output), attr 'dither_phase_available', value '0 90 180 270' dev 'ltc2688', channel 'voltage0' (output), attr 'dither_raw', value '0' dev 'ltc2688', channel 'voltage0' (output), attr 'dither_raw_available', value '[0 1 65535]' dev 'ltc2688', channel 'voltage0' (output), attr 'offset', value '0' dev 'ltc2688', channel 'voltage0' (output), attr 'powerdown', value '0' dev 'ltc2688', channel 'voltage0' (output), attr 'raw', value '0' dev 'ltc2688', channel 'voltage0' (output), attr 'raw_available', value '[0 1 65535]' dev 'ltc2688', channel 'voltage0' (output), attr 'scale', value '0.076293945' dev 'ltc2688', channel 'voltage0' (output), attr 'symbol', value '0' ``` So you can see that symbol attr which does not make sense to be there. And it's definitely not something wrong in the iio_attr app as the attr is shared by type. Also, as you suggested, not having the symbol attr when it does not make sense to have it also makes a lot of sense to me and that is one more plus point to have this as a per channel thing. Anyways, I will probably send the patch with things as I have now so you can have a felling of how it looks like. Unless you already tell me to just not have it as a shared_by_type attr (which I'm getting more and more convinced on my own; I guess I just need an extra push :D). - Nuno Sá
On Mon, 6 Dec 2021 11:07:55 +0000 "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > From: Jonathan Cameron <jic23@kernel.org> > > Sent: Sunday, December 5, 2021 7:04 PM > > To: Sa, Nuno <Nuno.Sa@analog.com> > > Cc: linux-iio@vger.kernel.org > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > [External] > > > > On Thu, 2 Dec 2021 15:37:40 +0000 > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > -----Original Message----- > > > > From: Sa, Nuno <Nuno.Sa@analog.com> > > > > Sent: Tuesday, November 30, 2021 3:43 PM > > > > To: Jonathan Cameron <jic23@kernel.org> > > > > Cc: linux-iio@vger.kernel.org > > > > Subject: RE: [RFC PATCH 0/1] LTC2688 support > > > > > > > > [External] > > > > > > > > > > > > > > > > > -----Original Message----- > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > Sent: Sunday, November 21, 2021 1:18 PM > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > Cc: linux-iio@vger.kernel.org > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > [External] > > > > > > > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > > > > > > Hi Jonathan, > > > > > > > > > > > > Thanks for your inputs... > > > > > > > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > > > Cc: linux-iio@vger.kernel.org > > > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > > > > > [External] > > > > > > > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > > > > > > > Hi Nuno, > > > > > > > > > > > > > > > The reason why this is a RFC is because I'm still waiting for > > > > proper > > > > > HW > > > > > > > > to test this thing. The reason why I'm sending this already is > > > > > because > > > > > > > > there's some non usual features which might require extra > > ABI. > > > > > > > Hence, > > > > > > > > while waiting I thought we could already speed up the > > process > > > > in > > > > > > > regards > > > > > > > > with the ABI. > > > > > > > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really to > > > > review > > > > > it. > > > > > > > > Naturally, if someone already wants to give some feedback, > > > > > that's > > > > > > > very > > > > > > > > much appreciated :) > > > > > > > > > > > > > > > > > > > > > > > Now, there are three main interfaces depending on the > > > > channel > > > > > > > mode: > > > > > > > > 1) default (no new ABI) > > > > > > > > 2) toggle mode > > > > > > > > 3) dither mode > > > > > > > > > > > > > > > > The channel mode will be a devicetree property as it does > > not > > > > > really > > > > > > > > make much sense to change between modes at runtime > > even > > > > > more > > > > > > > because the > > > > > > > > piece of HW we might want to control with a channel might > > be > > > > > > > different > > > > > > > > depending on the selected mode (I'm fairly sure on this > > > > between > > > > > > > toggle > > > > > > > > and other modes but not so sure between dither and > > default > > > > > mode). > > > > > > > > > > > > > > I agree on toggle vs dither definitely being different, but > > normal > > > > > you > > > > > > > could implement either as software toggle, or dither with a 0 > > > > > > > magnitude > > > > > > > sine wave. So might not be worth implementing default > > mode at > > > > > all. > > > > > > > No harm in doing so though if there are advantages to having > > it. > > > > > > > > > > > > My feeling is that we could probably have dither as the "default > > > > > mode". > > > > > > More on this below... > > > > > > > > > > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > > > > > > > * Toggle operation enables fast switching of a DAC output > > > > > between > > > > > > > two > > > > > > > > different DAC codes without any SPI transaction. Two codes > > are > > > > > set > > > > > > > in > > > > > > > > input_a and input_b and then the output switches > > according to > > > > > an > > > > > > > input > > > > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > > > > > > > out_voltageY_input_register > > > > > > > > - selects between input_a and input_b. After selecting one > > > > > register, > > > > > > > we > > > > > > > > can write the dac code in out_voltageY_raw. > > > > > > > > out_voltageY_toggle_en > > > > > > > > - Disable/Enable toggle mode. The reason why I think this > > one > > > > is > > > > > > > > important is because if we wanna change the 2 codes, we > > > > > should > > > > > > > first > > > > > > > > disable this, set the codes and only then enable the mode > > > > > back... > > > > > > > > As I'm writing this, It kind of came to me that we can > > probably > > > > > > > > achieve this with out_voltageY_powerdown attr (maybe > > > > takes a > > > > > bit > > > > > > > more > > > > > > > > time to see the outputs but...) > > > > > > > > > > > > > > Hmm. These corner cases always take a bit of figuring out. > > What > > > > > you > > > > > > > have > > > > > > > here is a bit 'device specific' for my liking. > > > > > > > > > > > > > > So there is precedence for ABI in this area, on the frequency > > > > > devices > > > > > > > but only > > > > > > > for devices we still haven't moved out of staging. For those > > we > > > > > > > needed a means > > > > > > > to define selectable phases for PSK - where the selection was > > > > > either > > > > > > > software or, > > > > > > > much like here, a selection pin. > > > > > > > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > > > > > > > so I guess the equivalent here would be > > > > > > > out_voltageY_raw0 > > > > > > > out_voltageY_raw1 > > > > > > > and the selection would be via something like > > > > > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > > > > > relevant if you have the software toggle. Any enable needed > > for > > > > > > > setting > > > > > > > can be done as part of the write sequence for the raw0 / > > raw1 > > > > and > > > > > > > should > > > > > > > ideally not be exposed to userspace (controls that require > > > > manual > > > > > > > sequencing > > > > > > > tend to be hard to use / document). > > > > > > > > > > > > Yeah, I thought about that. I was even thinking in having > > something > > > > > like > > > > > > *_amplitude for dither mode. In some cases, where we might > > be > > > > left > > > > > > in some non obvious state (eg: moved the select register to > > input b > > > > > and > > > > > > then we failed to set the code;), I prefer to leave things as > > flexible > > > > as > > > > > > possible for userspace. But I agree it adds up more complexity > > and > > > > in > > > > > > this case, I can just always go to 'input_a' when writing 'raw0'... > > > > > > > > > > > > > However, I'm not 100% sure it really maps to this case. What > > do > > > > > you > > > > > > > think? > > > > > > > > > > > > I think it can work. Though out_voltageY_symbol probably > > needs to > > > > > be > > > > > > shared by type to be coherent with what we might have with > > > > TGPx. > > > > > > > > > > That's fine. > > > > > > > > > > > Note the sw_toggle register has a bit mask of the channels we > > > > want > > > > > to > > > > > > toggle which means we can toggle multiple channels at the > > same > > > > > time. > > > > > > > > > > Using that wired up to buffer mode might make sense. You'd > > > > provide > > > > > multiple > > > > > buffers and allow channels to be selected into one of them at a > > time. > > > > > Each > > > > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > > > > > > > The same could be true for the software toggle. It'll get a bit > > fiddly > > > > > though. > > > > > > > > > > Perhaps this is an advanced feature to think about later... > > > > > > > > > > > It works the same with TGPx if you map multiple channels to > > the > > > > > same > > > > > > pin. > > > > > > > > > > > > There's also the question on how to handle this if a TGPx is > > > > provided? > > > > > > I guess it will just override the pin... But most likely having them > > > > both > > > > > > at the same time will lead to non desired results (unless we > > have a > > > > > > way to gate/ungate the clocks)... > > > > > I don't follow this bit. You mean TGPx and software toggle. As far > > as I > > > > > can > > > > > tell it's an either/or thing per channel. > > > > > > > > > > > > > Here I meant that if we have a TGPx pin bundled to some > > channel(s) > > > > we > > > > do not want to also dance with the sw_toggle bit of that channel. > > > > > > Just a note on this. After starting my tests with the device, I can > > actually > > > say that if we have a TGPx set in the channel settings register, the > > device > > > will pretty much ignore the sw_toggle settings for that channel. I > > could > > > see that the output voltage was not toggling at all. As soon as I > > removed > > > the TGPx setting, then dancing with the sw_toggle started to work. > > So, for > > > the HW this is not really an issue as it just ignores the sw_toggle. On a > > SW > > > perspective, I'm still not sure if I just ignore this and write whatever > > the > > > user sets or if I return some error code in the case a user tries to > > toggle > > > a channel with a binded TGPx. The first one is appealing as it makes > > the > > > code much simpler while OTHO it might make sense to be verbose > > here > > > otherwise the user might think something is happening when it > > isn't... > > > > If we are in a static configuration (see below) then just don't expose > > the > > software toggle control. Not having a big red button to press is the > > best way to > > tell userspace to not press the big red button... > > > Hmm, I get your point and that's valid if I have the sw_toggle as a per > channel attribute. Right now, I'm doing it as shared_by_type. The reason is > the sw_toggling is done by writing 1/0 in the toggle register and that register > is a bitmask being the mask 16bits wide. This allows you to toggle channels > at the same time in the same way you can do it if, say, you map 2,3 or more > channels to the same TGPx pin. Hmm. That will be tricky to support in a remotely 'general' way. > > However, I'm also not happy for having this as shared_by_type attr. One of > my complains is that it makes it look like a dither capable channel will also > support this (and we already agreed that sw_toggle does not make sense > for dither mode; so do not expose it). For instance the output of > 'iio_attr' on a dither enabled channel is: > > ``` > root@analog:~# iio_attr -c ltc2688 voltage0 > dev 'ltc2688', channel 'voltage0' (output), attr 'calibbias', value '0' > dev 'ltc2688', channel 'voltage0' (output), attr 'calibscale', value '0' > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_en', value '0' > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_frequency', value '32768' > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_frequency_available', value '32768 16384 8192 4096 2048' > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_phase', value '0' > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_phase_available', value '0 90 180 270' > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_raw', value '0' > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_raw_available', value '[0 1 65535]' > dev 'ltc2688', channel 'voltage0' (output), attr 'offset', value '0' > dev 'ltc2688', channel 'voltage0' (output), attr 'powerdown', value '0' > dev 'ltc2688', channel 'voltage0' (output), attr 'raw', value '0' > dev 'ltc2688', channel 'voltage0' (output), attr 'raw_available', value '[0 1 65535]' > dev 'ltc2688', channel 'voltage0' (output), attr 'scale', value '0.076293945' > dev 'ltc2688', channel 'voltage0' (output), attr 'symbol', value '0' > ``` > > So you can see that symbol attr which does not make sense to be there. And it's > definitely not something wrong in the iio_attr app as the attr is shared by type. > > Also, as you suggested, not having the symbol attr when it does not make sense > to have it also makes a lot of sense to me and that is one more plus point to have > this as a per channel thing. > > Anyways, I will probably send the patch with things as I have now so you can > have a felling of how it looks like. Unless you already tell me to just not have it > as a shared_by_type attr (which I'm getting more and more convinced on my own; > I guess I just need an extra push :D). Shared by type indeed doesn't work as it's a subset - however we would need a means to indicate what subset is used if we want to allow single write to toggle multiple. Mind you - the moment we get to multiple channels this should probably be using the chrdev route rather than sysfs and I'm not sure how that would map to this at all. So for now maybe take the view that software control of this is a weird feature anyway so make it per channel? Jonathan > > - Nuno Sá
On Mon, 6 Dec 2021 10:49:17 +0000 "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > -----Original Message----- > > From: Jonathan Cameron <jic23@kernel.org> > > Sent: Sunday, December 5, 2021 7:01 PM > > To: Sa, Nuno <Nuno.Sa@analog.com> > > Cc: linux-iio@vger.kernel.org > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > [External] > > > > On Tue, 30 Nov 2021 14:43:25 +0000 > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > Hi Nuno > > > > Hopefully I've not lost the plot on this! > > Not really. I had some days off so this was also set on hold from > my side. > > > > > -----Original Message----- > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > Sent: Sunday, November 21, 2021 1:18 PM > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > Cc: linux-iio@vger.kernel.org > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > [External] > > > > > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > > > > Hi Jonathan, > > > > > > > > > > Thanks for your inputs... > > > > > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > > Cc: linux-iio@vger.kernel.org > > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > > > [External] > > > > > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > > > > > Hi Nuno, > > > > > > > > > > > > > The reason why this is a RFC is because I'm still waiting for > > proper > > > > HW > > > > > > > to test this thing. The reason why I'm sending this already is > > > > because > > > > > > > there's some non usual features which might require extra > > ABI. > > > > > > Hence, > > > > > > > while waiting I thought we could already speed up the > > process in > > > > > > regards > > > > > > > with the ABI. > > > > > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really to > > review > > > > it. > > > > > > > Naturally, if someone already wants to give some feedback, > > > > that's > > > > > > very > > > > > > > much appreciated :) > > > > > > > > > > > > > > > > > > > > Now, there are three main interfaces depending on the > > channel > > > > > > mode: > > > > > > > 1) default (no new ABI) > > > > > > > 2) toggle mode > > > > > > > 3) dither mode > > > > > > > > > > > > > > The channel mode will be a devicetree property as it does not > > > > really > > > > > > > make much sense to change between modes at runtime > > even > > > > more > > > > > > because the > > > > > > > piece of HW we might want to control with a channel might > > be > > > > > > different > > > > > > > depending on the selected mode (I'm fairly sure on this > > between > > > > > > toggle > > > > > > > and other modes but not so sure between dither and default > > > > mode). > > > > > > > > > > > > I agree on toggle vs dither definitely being different, but normal > > > > you > > > > > > could implement either as software toggle, or dither with a 0 > > > > > > magnitude > > > > > > sine wave. So might not be worth implementing default mode > > at > > > > all. > > > > > > No harm in doing so though if there are advantages to having it. > > > > > > > > > > My feeling is that we could probably have dither as the "default > > > > mode". > > > > > More on this below... > > > > > > > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > > > > > * Toggle operation enables fast switching of a DAC output > > > > between > > > > > > two > > > > > > > different DAC codes without any SPI transaction. Two codes > > are > > > > set > > > > > > in > > > > > > > input_a and input_b and then the output switches according > > to > > > > an > > > > > > input > > > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > > > > > out_voltageY_input_register > > > > > > > - selects between input_a and input_b. After selecting one > > > > register, > > > > > > we > > > > > > > can write the dac code in out_voltageY_raw. > > > > > > > out_voltageY_toggle_en > > > > > > > - Disable/Enable toggle mode. The reason why I think this > > one is > > > > > > > important is because if we wanna change the 2 codes, we > > > > should > > > > > > first > > > > > > > disable this, set the codes and only then enable the mode > > > > back... > > > > > > > As I'm writing this, It kind of came to me that we can > > probably > > > > > > > achieve this with out_voltageY_powerdown attr (maybe > > takes a > > > > bit > > > > > > more > > > > > > > time to see the outputs but...) > > > > > > > > > > > > Hmm. These corner cases always take a bit of figuring out. > > What > > > > you > > > > > > have > > > > > > here is a bit 'device specific' for my liking. > > > > > > > > > > > > So there is precedence for ABI in this area, on the frequency > > > > devices > > > > > > but only > > > > > > for devices we still haven't moved out of staging. For those we > > > > > > needed a means > > > > > > to define selectable phases for PSK - where the selection was > > > > either > > > > > > software or, > > > > > > much like here, a selection pin. > > > > > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > > > > > so I guess the equivalent here would be > > > > > > out_voltageY_raw0 > > > > > > out_voltageY_raw1 > > > > > > and the selection would be via something like > > > > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > > > > relevant if you have the software toggle. Any enable needed > > for > > > > > > setting > > > > > > can be done as part of the write sequence for the raw0 / raw1 > > and > > > > > > should > > > > > > ideally not be exposed to userspace (controls that require > > manual > > > > > > sequencing > > > > > > tend to be hard to use / document). > > > > > > > > > > Yeah, I thought about that. I was even thinking in having > > something > > > > like > > > > > *_amplitude for dither mode. In some cases, where we might be > > left > > > > > in some non obvious state (eg: moved the select register to input > > b > > > > and > > > > > then we failed to set the code;), I prefer to leave things as > > flexible as > > > > > possible for userspace. But I agree it adds up more complexity > > and in > > > > > this case, I can just always go to 'input_a' when writing 'raw0'... > > > > > > > > > > > However, I'm not 100% sure it really maps to this case. What do > > > > you > > > > > > think? > > > > > > > > > > I think it can work. Though out_voltageY_symbol probably needs > > to > > > > be > > > > > shared by type to be coherent with what we might have with > > TGPx. > > > > > > > > That's fine. > > > > > > > > > Note the sw_toggle register has a bit mask of the channels we > > want > > > > to > > > > > toggle which means we can toggle multiple channels at the same > > > > time. > > > > > > > > Using that wired up to buffer mode might make sense. You'd > > provide > > > > multiple > > > > buffers and allow channels to be selected into one of them at a > > time. > > > > Each > > > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > > > > > The same could be true for the software toggle. It'll get a bit fiddly > > > > though. > > > > > > > > Perhaps this is an advanced feature to think about later... > > > > > > > > > It works the same with TGPx if you map multiple channels to the > > > > same > > > > > pin. > > > > > > > > > > There's also the question on how to handle this if a TGPx is > > provided? > > > > > I guess it will just override the pin... But most likely having them > > both > > > > > at the same time will lead to non desired results (unless we have > > a > > > > > way to gate/ungate the clocks)... > > > > I don't follow this bit. You mean TGPx and software toggle. As far > > as I > > > > can > > > > tell it's an either/or thing per channel. > > > > > > > > > > Here I meant that if we have a TGPx pin bundled to some channel(s) > > we > > > do not want to also dance with the sw_toggle bit of that channel. > > Ultimately, > > > that's on the user responsibility but we could also add some guards I > > guess. > > > I'm not sure if it's an either/or thing per channel... IIUC, we spoke > > about > > > making dither and default mode the same. That might complicate > > things a bit > > > as: > > > > > > 1) We should not force a user to specify a TGPx pin for those > > channels (since > > > it can also work with dithering disabled). > > > 2) Because of 1), we should also support sw_toggle for these > > channels since > > > someone might want to enable dither mode (at runtime) and the > > TGPx pin was > > > not given. Hence, we need to have a way to update the DAC using > > the sw_toggle. > > > > > > Did I understood things wrong? One thing that comes to my mind, is > > to return > > > error (eg: EPERM or ENOTSUPP) if someone tries to enable dither > > mode and > > > no TGPx pin was selected for that channel? Hence, we do not need > > to add > > > the sw_toggle ABI (out_voltage_symbol) for the default/dither > > mode. Or > > > maybe even better, we just expose the dither ABI if a TGPx pin is > > given over > > > dt (I try to explain the toggle/dither modes below; that might help > > you in > > > understanding my reasoning here)? > > > > > > Alternatively, we just keep the approach I have in this RFC and we > > keep the > > > 3 different modes (being mode a dt property; in the current state I'm > > using > > > a boolean to say a channel Is in toggle mode)... Maybe with the > > difference > > > that we allow sw_toggle for toggle enabled channels. > > > > The corner I'm not clear on is what we do if for example all TGPx pins > > are > > specified in DT. Is the mapping from channel to TGPx things in toggle > > mode > > always a function of the external circuit or do we want to make it > > runtime > > controllable? > > > > I'm absolutely fine if we just make it a dt property - particularly > > as those TGPx pins may well not be visible to the host processor. > > > > We probably do want to provide some options in dt for what they > > might be > > connnected to on the host. I'm guessing potentially a gpio, or a clk? > > For each TGPx pin (from the point you bind it to some channel), I'm > actually making it mandatory to have a clock (the reasoning being, if you > say some channel is controlled over TGPx [being for toggle or dither mode], > you need to have some input at the pin). I'm not really sure what the usecases behind toggle are... Using a clock with dither makes sense, but toggle might not be fixed frequency but driven by some other type of event. Still we don't have to support every usecase in an initial driver. Stick to a clock and see what requests you get for other input types later. > > I might not be doing it in the way you're thinking but you can have a > look in the actual series :) ... > ... > > > > So conclusions.. Hmm. Not strong ones yet, but for dither mode at > > > > least > > > > I think you want to link particular channels to a TGPx choice > > > > > > > > out_voltage0_raw > > > > out_voltage0_raw_available ( nice to have on DACs) > > > > > > I guess here you mean 'IIO_AVAIL_RANGE'? > > > > No, I mean providing the read_avail() callback and setting > > BIT(IIO_INFO_RAW) in info_mask_separate_available > > > > That's how we provide range for a channel except in some unusual > > corner cases and the internal interface for that is used when a DAC > > is being used via the consumer interface (so some other driver wants > > to set it's output). > > Yeah, I know :). I was just meaning 'IIO_AVAIL_RANGE' over 'IIO_AVAIL_LIST'. > I guess that was already obvious to you :). Ah. Got you. I'd forgotten about that - indeed IIO_AVAIL_RANGE > > > > > > > > out_voltage0_scale > > > > out_voltage0_dither_raw > > > > out_voltage0_dither_raw_available > > > > out_voltage0_dither_frequency > > > > out_voltage0_dither_frequency_available > > > > out_voltage0_dither_phase > > > > out_voltage0_dither_phase_available > > > > > > > Toggle mode is less clear to me but symbol approach plus TGPx in > > DT > > > > maybe works > > > > You could allow for software override to set the symbol. Interface > > to > > > > unset > > > > it being to write an empty string to _symbol. Maybe leave that for > > > > now. > > > > > > > > out_voltage0_raw0 > > > > out_voltage0_raw1 > > > > out_voltage0_scale > > > > out_voltage0_symbol > > > > > > Well, in short, I do agree with this ABI. And actually, for toggle mode, > > I think > > > this is more or less what we will have. For dither/default mode, > > there's still > > > the questions I raised above... Maybe, at the end, we will end up > > with 3 different > > > ABI's... > > > > Certainly possible. Nice to avoid if we can, but not if it means > > stretching > > things too far. > > > > > > > > I would only add this to the ABI: > > > * out_voltage0_dither_en > > > * out_voltage0_toggle_en > > > > > > Because if someone wants to change, let's say the dither frequency, > > the best way > > > to update things is to first disable dithering, update all the stuff, and > > then enable > > > it again... > > > > I'll go with 'maybe' for these. The use for changing things doesn't > > make sense to me > > unless we have multiple things to change at once. If it's just the > > frequency it > > would be more intuitive to have a write to that attribute do the > > disable, set value > > and enable dithering again without needing to do a dance with the > > interface. > > Yeah and that is something that can happen here (and probably the most > likely situation). For dither mode, you disable it, then you might want to > change all the parameters of your dither (amplitude, phase and frequency) > and then enable it again. > > For toggle mode, this means, disabling it, updating input_a and input_b and > enable it again. > > Anyways, I think we already have some discussion that enables me to send > the first version of this and we can continue from there. If all goes well, > it should be out by the end of the week. > Great, Jonathan
> From: Jonathan Cameron <Jonathan.Cameron@Huawei.com> > Sent: Monday, December 6, 2021 2:16 PM > To: Sa, Nuno <Nuno.Sa@analog.com> > Cc: Jonathan Cameron <jic23@kernel.org>; linux-iio@vger.kernel.org > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > [External] > > On Mon, 6 Dec 2021 10:49:17 +0000 > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > -----Original Message----- > > > From: Jonathan Cameron <jic23@kernel.org> > > > Sent: Sunday, December 5, 2021 7:01 PM > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > Cc: linux-iio@vger.kernel.org > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > [External] > > > > > > On Tue, 30 Nov 2021 14:43:25 +0000 > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > Hi Nuno > > > > > > Hopefully I've not lost the plot on this! > > > > Not really. I had some days off so this was also set on hold from > > my side. > > > > > > > -----Original Message----- > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > Sent: Sunday, November 21, 2021 1:18 PM > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > Cc: linux-iio@vger.kernel.org > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > [External] > > > > > > > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > > > > > > Hi Jonathan, > > > > > > > > > > > > Thanks for your inputs... > > > > > > > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > > > Cc: linux-iio@vger.kernel.org > > > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > > > > > [External] > > > > > > > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > > > > > > > Hi Nuno, > > > > > > > > > > > > > > > The reason why this is a RFC is because I'm still waiting for > > > proper > > > > > HW > > > > > > > > to test this thing. The reason why I'm sending this already > is > > > > > because > > > > > > > > there's some non usual features which might require > extra > > > ABI. > > > > > > > Hence, > > > > > > > > while waiting I thought we could already speed up the > > > process in > > > > > > > regards > > > > > > > > with the ABI. > > > > > > > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really to > > > review > > > > > it. > > > > > > > > Naturally, if someone already wants to give some > feedback, > > > > > that's > > > > > > > very > > > > > > > > much appreciated :) > > > > > > > > > > > > > > > > > > > > > > > Now, there are three main interfaces depending on the > > > channel > > > > > > > mode: > > > > > > > > 1) default (no new ABI) > > > > > > > > 2) toggle mode > > > > > > > > 3) dither mode > > > > > > > > > > > > > > > > The channel mode will be a devicetree property as it does > not > > > > > really > > > > > > > > make much sense to change between modes at runtime > > > even > > > > > more > > > > > > > because the > > > > > > > > piece of HW we might want to control with a channel > might > > > be > > > > > > > different > > > > > > > > depending on the selected mode (I'm fairly sure on this > > > between > > > > > > > toggle > > > > > > > > and other modes but not so sure between dither and > default > > > > > mode). > > > > > > > > > > > > > > I agree on toggle vs dither definitely being different, but > normal > > > > > you > > > > > > > could implement either as software toggle, or dither with a > 0 > > > > > > > magnitude > > > > > > > sine wave. So might not be worth implementing default > mode > > > at > > > > > all. > > > > > > > No harm in doing so though if there are advantages to > having it. > > > > > > > > > > > > My feeling is that we could probably have dither as the > "default > > > > > mode". > > > > > > More on this below... > > > > > > > > > > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > > > > > > > * Toggle operation enables fast switching of a DAC output > > > > > between > > > > > > > two > > > > > > > > different DAC codes without any SPI transaction. Two > codes > > > are > > > > > set > > > > > > > in > > > > > > > > input_a and input_b and then the output switches > according > > > to > > > > > an > > > > > > > input > > > > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > > > > > > > out_voltageY_input_register > > > > > > > > - selects between input_a and input_b. After selecting > one > > > > > register, > > > > > > > we > > > > > > > > can write the dac code in out_voltageY_raw. > > > > > > > > out_voltageY_toggle_en > > > > > > > > - Disable/Enable toggle mode. The reason why I think this > > > one is > > > > > > > > important is because if we wanna change the 2 codes, > we > > > > > should > > > > > > > first > > > > > > > > disable this, set the codes and only then enable the > mode > > > > > back... > > > > > > > > As I'm writing this, It kind of came to me that we can > > > probably > > > > > > > > achieve this with out_voltageY_powerdown attr (maybe > > > takes a > > > > > bit > > > > > > > more > > > > > > > > time to see the outputs but...) > > > > > > > > > > > > > > Hmm. These corner cases always take a bit of figuring out. > > > What > > > > > you > > > > > > > have > > > > > > > here is a bit 'device specific' for my liking. > > > > > > > > > > > > > > So there is precedence for ABI in this area, on the > frequency > > > > > devices > > > > > > > but only > > > > > > > for devices we still haven't moved out of staging. For those > we > > > > > > > needed a means > > > > > > > to define selectable phases for PSK - where the selection > was > > > > > either > > > > > > > software or, > > > > > > > much like here, a selection pin. > > > > > > > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > > > > > > > so I guess the equivalent here would be > > > > > > > out_voltageY_raw0 > > > > > > > out_voltageY_raw1 > > > > > > > and the selection would be via something like > > > > > > > out_voltageY_symbol (0 or 1 in this case). - note this is only > > > > > > > relevant if you have the software toggle. Any enable > needed > > > for > > > > > > > setting > > > > > > > can be done as part of the write sequence for the raw0 / > raw1 > > > and > > > > > > > should > > > > > > > ideally not be exposed to userspace (controls that require > > > manual > > > > > > > sequencing > > > > > > > tend to be hard to use / document). > > > > > > > > > > > > Yeah, I thought about that. I was even thinking in having > > > something > > > > > like > > > > > > *_amplitude for dither mode. In some cases, where we might > be > > > left > > > > > > in some non obvious state (eg: moved the select register to > input > > > b > > > > > and > > > > > > then we failed to set the code;), I prefer to leave things as > > > flexible as > > > > > > possible for userspace. But I agree it adds up more complexity > > > and in > > > > > > this case, I can just always go to 'input_a' when writing > 'raw0'... > > > > > > > > > > > > > However, I'm not 100% sure it really maps to this case. > What do > > > > > you > > > > > > > think? > > > > > > > > > > > > I think it can work. Though out_voltageY_symbol probably > needs > > > to > > > > > be > > > > > > shared by type to be coherent with what we might have with > > > TGPx. > > > > > > > > > > That's fine. > > > > > > > > > > > Note the sw_toggle register has a bit mask of the channels > we > > > want > > > > > to > > > > > > toggle which means we can toggle multiple channels at the > same > > > > > time. > > > > > > > > > > Using that wired up to buffer mode might make sense. You'd > > > provide > > > > > multiple > > > > > buffers and allow channels to be selected into one of them at a > > > time. > > > > > Each > > > > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > > > > > > > The same could be true for the software toggle. It'll get a bit > fiddly > > > > > though. > > > > > > > > > > Perhaps this is an advanced feature to think about later... > > > > > > > > > > > It works the same with TGPx if you map multiple channels to > the > > > > > same > > > > > > pin. > > > > > > > > > > > > There's also the question on how to handle this if a TGPx is > > > provided? > > > > > > I guess it will just override the pin... But most likely having > them > > > both > > > > > > at the same time will lead to non desired results (unless we > have > > > a > > > > > > way to gate/ungate the clocks)... > > > > > I don't follow this bit. You mean TGPx and software toggle. As > far > > > as I > > > > > can > > > > > tell it's an either/or thing per channel. > > > > > > > > > > > > > Here I meant that if we have a TGPx pin bundled to some > channel(s) > > > we > > > > do not want to also dance with the sw_toggle bit of that channel. > > > Ultimately, > > > > that's on the user responsibility but we could also add some > guards I > > > guess. > > > > I'm not sure if it's an either/or thing per channel... IIUC, we spoke > > > about > > > > making dither and default mode the same. That might complicate > > > things a bit > > > > as: > > > > > > > > 1) We should not force a user to specify a TGPx pin for those > > > channels (since > > > > it can also work with dithering disabled). > > > > 2) Because of 1), we should also support sw_toggle for these > > > channels since > > > > someone might want to enable dither mode (at runtime) and the > > > TGPx pin was > > > > not given. Hence, we need to have a way to update the DAC > using > > > the sw_toggle. > > > > > > > > Did I understood things wrong? One thing that comes to my > mind, is > > > to return > > > > error (eg: EPERM or ENOTSUPP) if someone tries to enable dither > > > mode and > > > > no TGPx pin was selected for that channel? Hence, we do not > need > > > to add > > > > the sw_toggle ABI (out_voltage_symbol) for the default/dither > > > mode. Or > > > > maybe even better, we just expose the dither ABI if a TGPx pin is > > > given over > > > > dt (I try to explain the toggle/dither modes below; that might > help > > > you in > > > > understanding my reasoning here)? > > > > > > > > Alternatively, we just keep the approach I have in this RFC and > we > > > keep the > > > > 3 different modes (being mode a dt property; in the current state > I'm > > > using > > > > a boolean to say a channel Is in toggle mode)... Maybe with the > > > difference > > > > that we allow sw_toggle for toggle enabled channels. > > > > > > The corner I'm not clear on is what we do if for example all TGPx > pins > > > are > > > specified in DT. Is the mapping from channel to TGPx things in > toggle > > > mode > > > always a function of the external circuit or do we want to make it > > > runtime > > > controllable? > > > > > > I'm absolutely fine if we just make it a dt property - particularly > > > as those TGPx pins may well not be visible to the host processor. > > > > > > We probably do want to provide some options in dt for what they > > > might be > > > connnected to on the host. I'm guessing potentially a gpio, or a clk? > > > > For each TGPx pin (from the point you bind it to some channel), I'm > > actually making it mandatory to have a clock (the reasoning being, if > you > > say some channel is controlled over TGPx [being for toggle or dither > mode], > > you need to have some input at the pin). > > I'm not really sure what the usecases behind toggle are... Using a clock > with dither makes sense, but toggle might not be fixed frequency but > driven by some other type of event. Taken from the datasheet (usecases for toggle mode): "Examples include injection of a small ac bias, or independently switching between on and off states". A clock seems to fit even though I get your point that it might not fit all usecases for this. In that case, maybe sw_toggle can be enough :). Anyways, agreed that we do not have to support all the stuff at the very beginning and it's probably a bad idea specially in cases like this where we are not sure about all possible usecases. - Nuno Sá
> -----Original Message----- > From: Jonathan Cameron <Jonathan.Cameron@Huawei.com> > Sent: Monday, December 6, 2021 2:10 PM > To: Sa, Nuno <Nuno.Sa@analog.com> > Cc: Jonathan Cameron <jic23@kernel.org>; linux-iio@vger.kernel.org > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > [External] > > On Mon, 6 Dec 2021 11:07:55 +0000 > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > From: Jonathan Cameron <jic23@kernel.org> > > > Sent: Sunday, December 5, 2021 7:04 PM > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > Cc: linux-iio@vger.kernel.org > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > [External] > > > > > > On Thu, 2 Dec 2021 15:37:40 +0000 > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > > > -----Original Message----- > > > > > From: Sa, Nuno <Nuno.Sa@analog.com> > > > > > Sent: Tuesday, November 30, 2021 3:43 PM > > > > > To: Jonathan Cameron <jic23@kernel.org> > > > > > Cc: linux-iio@vger.kernel.org > > > > > Subject: RE: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > [External] > > > > > > > > > > > > > > > > > > > > > -----Original Message----- > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > > Sent: Sunday, November 21, 2021 1:18 PM > > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > > Cc: linux-iio@vger.kernel.org > > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > > > [External] > > > > > > > > > > > > On Mon, 15 Nov 2021 10:28:51 +0000 > > > > > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote: > > > > > > > > > > > > > Hi Jonathan, > > > > > > > > > > > > > > Thanks for your inputs... > > > > > > > > > > > > > > > From: Jonathan Cameron <jic23@kernel.org> > > > > > > > > Sent: Friday, November 12, 2021 5:15 PM > > > > > > > > To: Sa, Nuno <Nuno.Sa@analog.com> > > > > > > > > Cc: linux-iio@vger.kernel.org > > > > > > > > Subject: Re: [RFC PATCH 0/1] LTC2688 support > > > > > > > > > > > > > > > > [External] > > > > > > > > > > > > > > > > On Thu, 11 Nov 2021 12:00:42 +0100 > > > > > > > > Nuno Sá <nuno.sa@analog.com> wrote: > > > > > > > > > > > > > > > > Hi Nuno, > > > > > > > > > > > > > > > > > The reason why this is a RFC is because I'm still waiting > for > > > > > proper > > > > > > HW > > > > > > > > > to test this thing. The reason why I'm sending this > already is > > > > > > because > > > > > > > > > there's some non usual features which might require > extra > > > ABI. > > > > > > > > Hence, > > > > > > > > > while waiting I thought we could already speed up the > > > process > > > > > in > > > > > > > > regards > > > > > > > > > with the ABI. > > > > > > > > > > > > > > > > Wise move as this is an unusual beast :) > > > > > > > > > > > > > > > > > > > > > > > > > > I still pushed the driver but the intent here is not really > to > > > > > review > > > > > > it. > > > > > > > > > Naturally, if someone already wants to give some > feedback, > > > > > > that's > > > > > > > > very > > > > > > > > > much appreciated :) > > > > > > > > > > > > > > > > > > > > > > > > > > Now, there are three main interfaces depending on the > > > > > channel > > > > > > > > mode: > > > > > > > > > 1) default (no new ABI) > > > > > > > > > 2) toggle mode > > > > > > > > > 3) dither mode > > > > > > > > > > > > > > > > > > The channel mode will be a devicetree property as it > does > > > not > > > > > > really > > > > > > > > > make much sense to change between modes at runtime > > > even > > > > > > more > > > > > > > > because the > > > > > > > > > piece of HW we might want to control with a channel > might > > > be > > > > > > > > different > > > > > > > > > depending on the selected mode (I'm fairly sure on this > > > > > between > > > > > > > > toggle > > > > > > > > > and other modes but not so sure between dither and > > > default > > > > > > mode). > > > > > > > > > > > > > > > > I agree on toggle vs dither definitely being different, but > > > normal > > > > > > you > > > > > > > > could implement either as software toggle, or dither with > a 0 > > > > > > > > magnitude > > > > > > > > sine wave. So might not be worth implementing default > > > mode at > > > > > > all. > > > > > > > > No harm in doing so though if there are advantages to > having > > > it. > > > > > > > > > > > > > > My feeling is that we could probably have dither as the > "default > > > > > > mode". > > > > > > > More on this below... > > > > > > > > > > > > > > > > > > > > > > > > > toggle mode special ABI: > > > > > > > > > > > > > > > > > > * Toggle operation enables fast switching of a DAC > output > > > > > > between > > > > > > > > two > > > > > > > > > different DAC codes without any SPI transaction. Two > codes > > > are > > > > > > set > > > > > > > > in > > > > > > > > > input_a and input_b and then the output switches > > > according to > > > > > > an > > > > > > > > input > > > > > > > > > signal (input_a -> clk high; input_b -> clk low). > > > > > > > > > > > > > > > > > > out_voltageY_input_register > > > > > > > > > - selects between input_a and input_b. After selecting > one > > > > > > register, > > > > > > > > we > > > > > > > > > can write the dac code in out_voltageY_raw. > > > > > > > > > out_voltageY_toggle_en > > > > > > > > > - Disable/Enable toggle mode. The reason why I think > this > > > one > > > > > is > > > > > > > > > important is because if we wanna change the 2 codes, > we > > > > > > should > > > > > > > > first > > > > > > > > > disable this, set the codes and only then enable the > mode > > > > > > back... > > > > > > > > > As I'm writing this, It kind of came to me that we can > > > probably > > > > > > > > > achieve this with out_voltageY_powerdown attr > (maybe > > > > > takes a > > > > > > bit > > > > > > > > more > > > > > > > > > time to see the outputs but...) > > > > > > > > > > > > > > > > Hmm. These corner cases always take a bit of figuring out. > > > What > > > > > > you > > > > > > > > have > > > > > > > > here is a bit 'device specific' for my liking. > > > > > > > > > > > > > > > > So there is precedence for ABI in this area, on the > frequency > > > > > > devices > > > > > > > > but only > > > > > > > > for devices we still haven't moved out of staging. For > those > > > we > > > > > > > > needed a means > > > > > > > > to define selectable phases for PSK - where the selection > was > > > > > > either > > > > > > > > software or, > > > > > > > > much like here, a selection pin. > > > > > > > > > > > > > > > > out_altvotage0_phase0 etc > > > > > > > > > > > > > > > > so I guess the equivalent here would be > > > > > > > > out_voltageY_raw0 > > > > > > > > out_voltageY_raw1 > > > > > > > > and the selection would be via something like > > > > > > > > out_voltageY_symbol (0 or 1 in this case). - note this is > only > > > > > > > > relevant if you have the software toggle. Any enable > needed > > > for > > > > > > > > setting > > > > > > > > can be done as part of the write sequence for the raw0 / > > > raw1 > > > > > and > > > > > > > > should > > > > > > > > ideally not be exposed to userspace (controls that require > > > > > manual > > > > > > > > sequencing > > > > > > > > tend to be hard to use / document). > > > > > > > > > > > > > > Yeah, I thought about that. I was even thinking in having > > > something > > > > > > like > > > > > > > *_amplitude for dither mode. In some cases, where we > might > > > be > > > > > left > > > > > > > in some non obvious state (eg: moved the select register to > > > input b > > > > > > and > > > > > > > then we failed to set the code;), I prefer to leave things as > > > flexible > > > > > as > > > > > > > possible for userspace. But I agree it adds up more > complexity > > > and > > > > > in > > > > > > > this case, I can just always go to 'input_a' when writing > 'raw0'... > > > > > > > > > > > > > > > However, I'm not 100% sure it really maps to this case. > What > > > do > > > > > > you > > > > > > > > think? > > > > > > > > > > > > > > I think it can work. Though out_voltageY_symbol probably > > > needs to > > > > > > be > > > > > > > shared by type to be coherent with what we might have > with > > > > > TGPx. > > > > > > > > > > > > That's fine. > > > > > > > > > > > > > Note the sw_toggle register has a bit mask of the channels > we > > > > > want > > > > > > to > > > > > > > toggle which means we can toggle multiple channels at the > > > same > > > > > > time. > > > > > > > > > > > > Using that wired up to buffer mode might make sense. You'd > > > > > provide > > > > > > multiple > > > > > > buffers and allow channels to be selected into one of them at > a > > > time. > > > > > > Each > > > > > > buffer is then tied to a different toggle (TGP0, TGP1, etc) > > > > > > > > > > > > The same could be true for the software toggle. It'll get a bit > > > fiddly > > > > > > though. > > > > > > > > > > > > Perhaps this is an advanced feature to think about later... > > > > > > > > > > > > > It works the same with TGPx if you map multiple channels > to > > > the > > > > > > same > > > > > > > pin. > > > > > > > > > > > > > > There's also the question on how to handle this if a TGPx is > > > > > provided? > > > > > > > I guess it will just override the pin... But most likely having > them > > > > > both > > > > > > > at the same time will lead to non desired results (unless we > > > have a > > > > > > > way to gate/ungate the clocks)... > > > > > > I don't follow this bit. You mean TGPx and software toggle. As > far > > > as I > > > > > > can > > > > > > tell it's an either/or thing per channel. > > > > > > > > > > > > > > > > Here I meant that if we have a TGPx pin bundled to some > > > channel(s) > > > > > we > > > > > do not want to also dance with the sw_toggle bit of that > channel. > > > > > > > > Just a note on this. After starting my tests with the device, I can > > > actually > > > > say that if we have a TGPx set in the channel settings register, the > > > device > > > > will pretty much ignore the sw_toggle settings for that channel. I > > > could > > > > see that the output voltage was not toggling at all. As soon as I > > > removed > > > > the TGPx setting, then dancing with the sw_toggle started to > work. > > > So, for > > > > the HW this is not really an issue as it just ignores the sw_toggle. > On a > > > SW > > > > perspective, I'm still not sure if I just ignore this and write > whatever > > > the > > > > user sets or if I return some error code in the case a user tries to > > > toggle > > > > a channel with a binded TGPx. The first one is appealing as it > makes > > > the > > > > code much simpler while OTHO it might make sense to be > verbose > > > here > > > > otherwise the user might think something is happening when it > > > isn't... > > > > > > If we are in a static configuration (see below) then just don't > expose > > > the > > > software toggle control. Not having a big red button to press is the > > > best way to > > > tell userspace to not press the big red button... > > > > > > Hmm, I get your point and that's valid if I have the sw_toggle as a per > > channel attribute. Right now, I'm doing it as shared_by_type. The > reason is > > the sw_toggling is done by writing 1/0 in the toggle register and that > register > > is a bitmask being the mask 16bits wide. This allows you to toggle > channels > > at the same time in the same way you can do it if, say, you map 2,3 or > more > > channels to the same TGPx pin. > > Hmm. That will be tricky to support in a remotely 'general' way. > > > > > However, I'm also not happy for having this as shared_by_type attr. > One of > > my complains is that it makes it look like a dither capable channel will > also > > support this (and we already agreed that sw_toggle does not make > sense > > for dither mode; so do not expose it). For instance the output of > > 'iio_attr' on a dither enabled channel is: > > > > ``` > > root@analog:~# iio_attr -c ltc2688 voltage0 > > dev 'ltc2688', channel 'voltage0' (output), attr 'calibbias', value '0' > > dev 'ltc2688', channel 'voltage0' (output), attr 'calibscale', value '0' > > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_en', value '0' > > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_frequency', > value '32768' > > dev 'ltc2688', channel 'voltage0' (output), attr > 'dither_frequency_available', value '32768 16384 8192 4096 2048' > > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_phase', value '0' > > dev 'ltc2688', channel 'voltage0' (output), attr > 'dither_phase_available', value '0 90 180 270' > > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_raw', value '0' > > dev 'ltc2688', channel 'voltage0' (output), attr 'dither_raw_available', > value '[0 1 65535]' > > dev 'ltc2688', channel 'voltage0' (output), attr 'offset', value '0' > > dev 'ltc2688', channel 'voltage0' (output), attr 'powerdown', value '0' > > dev 'ltc2688', channel 'voltage0' (output), attr 'raw', value '0' > > dev 'ltc2688', channel 'voltage0' (output), attr 'raw_available', value > '[0 1 65535]' > > dev 'ltc2688', channel 'voltage0' (output), attr 'scale', value > '0.076293945' > > dev 'ltc2688', channel 'voltage0' (output), attr 'symbol', value '0' > > ``` > > > > So you can see that symbol attr which does not make sense to be > there. And it's > > definitely not something wrong in the iio_attr app as the attr is > shared by type. > > > > Also, as you suggested, not having the symbol attr when it does not > make sense > > to have it also makes a lot of sense to me and that is one more plus > point to have > > this as a per channel thing. > > > > Anyways, I will probably send the patch with things as I have now so > you can > > have a felling of how it looks like. Unless you already tell me to just > not have it > > as a shared_by_type attr (which I'm getting more and more > convinced on my own; > > I guess I just need an extra push :D). > > Shared by type indeed doesn't work as it's a subset - however we > would need > a means to indicate what subset is used if we want to allow single write > to toggle multiple. Mind you - the moment we get to multiple > channels > this should probably be using the chrdev route rather than sysfs and > I'm > not sure how that would map to this at all. If someone really wants to toggle multiple channels through SW, one route would also be to use TGPx (mapping it to multiple channels) and use some of the host GPIOs to control the pin. Not nice as we would still need to provide a dummy clock to make the driver "happy" but it would be a possible workaround. This would only fail if all TGPx are already allocated for dither channels but that's very unlikely. OTHO, if we are doing the toggle through SW maybe our timings are not that strict so toggling all the channels in a loop is not that bad... Well, this is just wondering and playing "if" games so better to keep it simple and worry about this if such a usecase ever pops up. > So for now maybe take the view that software control of this is a weird > feature > anyway so make it per channel? Agreed, will make it per channel and only expose it if a TGPx mapping is not present. I was leaning in that direction anyways :). - Nuno Sá