| Message ID | 1548762199-7065-2-git-send-email-yash.shah@sifive.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | PWM support for HiFive Unleashed | expand |
On Tue, Jan 29, 2019 at 05:13:18PM +0530, Yash Shah wrote: > DT documentation for PWM controller added. > > Signed-off-by: Wesley W. Terpstra <wesley@sifive.com> > [Atish: Compatible string update] > Signed-off-by: Atish Patra <atish.patra@wdc.com> > Signed-off-by: Yash Shah <yash.shah@sifive.com> > --- > .../devicetree/bindings/pwm/pwm-sifive.txt | 33 ++++++++++++++++++++++ > 1 file changed, 33 insertions(+) > create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > new file mode 100644 > index 0000000..8dcb40d > --- /dev/null > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > @@ -0,0 +1,33 @@ > +SiFive PWM controller > + > +Unlike most other PWM controllers, the SiFive PWM controller currently only > +supports one period for all channels in the PWM. This is set globally in DTS. You can simply drop this if the first user can set this using the usual interface. Don't you like this suggestion that I already made a few times now? Did you consider to make the driver support only a single output with a more flexible period setting? > +The period also has significant restrictions on the values it can achieve, > +which the driver rounds to the nearest achievable frequency. Rounding a period to a frequency sounds wrong. Best regards Uwe
On Wed, Jan 30, 2019 at 1:44 PM Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote: > > On Tue, Jan 29, 2019 at 05:13:18PM +0530, Yash Shah wrote: > > DT documentation for PWM controller added. > > > > Signed-off-by: Wesley W. Terpstra <wesley@sifive.com> > > [Atish: Compatible string update] > > Signed-off-by: Atish Patra <atish.patra@wdc.com> > > Signed-off-by: Yash Shah <yash.shah@sifive.com> > > --- > > .../devicetree/bindings/pwm/pwm-sifive.txt | 33 ++++++++++++++++++++++ > > 1 file changed, 33 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > new file mode 100644 > > index 0000000..8dcb40d > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > @@ -0,0 +1,33 @@ > > +SiFive PWM controller > > + > > +Unlike most other PWM controllers, the SiFive PWM controller currently only > > +supports one period for all channels in the PWM. This is set globally in DTS. > > You can simply drop this if the first user can set this using the usual > interface. Don't you like this suggestion that I already made a few > times now? > > Did you consider to make the driver support only a single output with a > more flexible period setting? We cannot consider supporting only single output since we have boards that use the additional PWM channels to control individual LED brightness of a tri-color LED. If we go down to one channel, then we can't control the brightness of the individual LEDs. It will break the use case. I am considering the below approach, let me know if it's fine by you. - Drop the global period property and allow the only first user to change period using the usual interface. - A note in the binding that all PWMs need to run at the same period. If the driver already refuses to apply incompatible periods, the users are going to notice that they've got the DT wrong. - In driver code, count the users using the .request and .free callbacks. Based on this, allow changes to period iff the user count is one. > > > +The period also has significant restrictions on the values it can achieve, > > +which the driver rounds to the nearest achievable frequency. > > Rounding a period to a frequency sounds wrong. > > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König | > Industrial Linux Solutions | http://www.pengutronix.de/ |
On Wed, Feb 06, 2019 at 04:18:47PM +0530, Yash Shah wrote: > On Wed, Jan 30, 2019 at 1:44 PM Uwe Kleine-König > <u.kleine-koenig@pengutronix.de> wrote: > > > > On Tue, Jan 29, 2019 at 05:13:18PM +0530, Yash Shah wrote: > > > DT documentation for PWM controller added. > > > > > > Signed-off-by: Wesley W. Terpstra <wesley@sifive.com> > > > [Atish: Compatible string update] > > > Signed-off-by: Atish Patra <atish.patra@wdc.com> > > > Signed-off-by: Yash Shah <yash.shah@sifive.com> > > > --- > > > .../devicetree/bindings/pwm/pwm-sifive.txt | 33 ++++++++++++++++++++++ > > > 1 file changed, 33 insertions(+) > > > create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > new file mode 100644 > > > index 0000000..8dcb40d > > > --- /dev/null > > > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > @@ -0,0 +1,33 @@ > > > +SiFive PWM controller > > > + > > > +Unlike most other PWM controllers, the SiFive PWM controller currently only > > > +supports one period for all channels in the PWM. This is set globally in DTS. > > > > You can simply drop this if the first user can set this using the usual > > interface. Don't you like this suggestion that I already made a few > > times now? > > > > Did you consider to make the driver support only a single output with a > > more flexible period setting? > > We cannot consider supporting only single output since we have boards that > use the additional PWM channels to control individual LED brightness > of a tri-color LED. > If we go down to one channel, then we can't control the brightness of > the individual LEDs. > It will break the use case. OK. > I am considering the below approach, let me know if it's fine by you. > > - Drop the global period property and allow the only first user to change period > using the usual interface. > - A note in the binding that all PWMs need to run at the same > period. If the driver already refuses to apply incompatible periods, > the users are going to notice that they've got the DT wrong. > - In driver code, count the users using the .request and .free callbacks. > Based on this, allow changes to period iff the user count is one. Not sure you need to point this limitation in the binding doc. Other than that this is fine. Best regards Uwe
On Wed, Feb 06, 2019 at 12:07:30PM +0100, Uwe Kleine-König wrote: > On Wed, Feb 06, 2019 at 04:18:47PM +0530, Yash Shah wrote: > > On Wed, Jan 30, 2019 at 1:44 PM Uwe Kleine-König > > <u.kleine-koenig@pengutronix.de> wrote: > > > > > > On Tue, Jan 29, 2019 at 05:13:18PM +0530, Yash Shah wrote: > > > > DT documentation for PWM controller added. > > > > > > > > Signed-off-by: Wesley W. Terpstra <wesley@sifive.com> > > > > [Atish: Compatible string update] > > > > Signed-off-by: Atish Patra <atish.patra@wdc.com> > > > > Signed-off-by: Yash Shah <yash.shah@sifive.com> > > > > --- > > > > .../devicetree/bindings/pwm/pwm-sifive.txt | 33 ++++++++++++++++++++++ > > > > 1 file changed, 33 insertions(+) > > > > create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > new file mode 100644 > > > > index 0000000..8dcb40d > > > > --- /dev/null > > > > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > @@ -0,0 +1,33 @@ > > > > +SiFive PWM controller > > > > + > > > > +Unlike most other PWM controllers, the SiFive PWM controller currently only > > > > +supports one period for all channels in the PWM. This is set globally in DTS. > > > > > > You can simply drop this if the first user can set this using the usual > > > interface. Don't you like this suggestion that I already made a few > > > times now? > > > > > > Did you consider to make the driver support only a single output with a > > > more flexible period setting? > > > > We cannot consider supporting only single output since we have boards that > > use the additional PWM channels to control individual LED brightness > > of a tri-color LED. > > If we go down to one channel, then we can't control the brightness of > > the individual LEDs. > > It will break the use case. > > OK. > > > I am considering the below approach, let me know if it's fine by you. > > > > - Drop the global period property and allow the only first user to change period > > using the usual interface. > > - A note in the binding that all PWMs need to run at the same > > period. If the driver already refuses to apply incompatible periods, > > the users are going to notice that they've got the DT wrong. > > - In driver code, count the users using the .request and .free callbacks. > > Based on this, allow changes to period iff the user count is one. > > Not sure you need to point this limitation in the binding doc. Other > than that this is fine. I think it's useful to point this out in the binding documentation since it's something that device tree writers will want to know. Thierry
On Wed, Feb 06, 2019 at 01:40:55PM +0100, Thierry Reding wrote: > On Wed, Feb 06, 2019 at 12:07:30PM +0100, Uwe Kleine-König wrote: > > On Wed, Feb 06, 2019 at 04:18:47PM +0530, Yash Shah wrote: > > > On Wed, Jan 30, 2019 at 1:44 PM Uwe Kleine-König > > > <u.kleine-koenig@pengutronix.de> wrote: > > > > > > > > On Tue, Jan 29, 2019 at 05:13:18PM +0530, Yash Shah wrote: > > > > > DT documentation for PWM controller added. > > > > > > > > > > Signed-off-by: Wesley W. Terpstra <wesley@sifive.com> > > > > > [Atish: Compatible string update] > > > > > Signed-off-by: Atish Patra <atish.patra@wdc.com> > > > > > Signed-off-by: Yash Shah <yash.shah@sifive.com> > > > > > --- > > > > > .../devicetree/bindings/pwm/pwm-sifive.txt | 33 ++++++++++++++++++++++ > > > > > 1 file changed, 33 insertions(+) > > > > > create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > new file mode 100644 > > > > > index 0000000..8dcb40d > > > > > --- /dev/null > > > > > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > @@ -0,0 +1,33 @@ > > > > > +SiFive PWM controller > > > > > + > > > > > +Unlike most other PWM controllers, the SiFive PWM controller currently only > > > > > +supports one period for all channels in the PWM. This is set globally in DTS. > > > > > > > > You can simply drop this if the first user can set this using the usual > > > > interface. Don't you like this suggestion that I already made a few > > > > times now? > > > > > > > > Did you consider to make the driver support only a single output with a > > > > more flexible period setting? > > > > > > We cannot consider supporting only single output since we have boards that > > > use the additional PWM channels to control individual LED brightness > > > of a tri-color LED. > > > If we go down to one channel, then we can't control the brightness of > > > the individual LEDs. > > > It will break the use case. > > > > OK. > > > > > I am considering the below approach, let me know if it's fine by you. > > > > > > - Drop the global period property and allow the only first user to change period > > > using the usual interface. > > > - A note in the binding that all PWMs need to run at the same > > > period. If the driver already refuses to apply incompatible periods, > > > the users are going to notice that they've got the DT wrong. > > > - In driver code, count the users using the .request and .free callbacks. > > > Based on this, allow changes to period iff the user count is one. > > > > Not sure you need to point this limitation in the binding doc. Other > > than that this is fine. > > I think it's useful to point this out in the binding documentation since > it's something that device tree writers will want to know. OK, we're talking about an FPGA implementation but I still think if the dt-author is the first to know about this limitation this is too late. The hardware designer must know about that, and they don't look into the bindind documentation. The binding documentation should IMHO only describe the binding and functional limitiations of the device are out of scope. The binding for the Freescale network interface doesn't describe that it only supports 480 MBit/s in its GHz mode, and that's good. The binding for i2c devices doesn't describe that a reboot in the middle of a transfer might block the bus. The target for the binding documentation is to document how a given device is described in a device tree. It's not there to duplicate information that belongs in the reference manual. Best regards Uwe
On Wed, Feb 06, 2019 at 04:38:54PM +0100, Uwe Kleine-König wrote: > On Wed, Feb 06, 2019 at 01:40:55PM +0100, Thierry Reding wrote: > > On Wed, Feb 06, 2019 at 12:07:30PM +0100, Uwe Kleine-König wrote: > > > On Wed, Feb 06, 2019 at 04:18:47PM +0530, Yash Shah wrote: > > > > On Wed, Jan 30, 2019 at 1:44 PM Uwe Kleine-König > > > > <u.kleine-koenig@pengutronix.de> wrote: > > > > > > > > > > On Tue, Jan 29, 2019 at 05:13:18PM +0530, Yash Shah wrote: > > > > > > DT documentation for PWM controller added. > > > > > > > > > > > > Signed-off-by: Wesley W. Terpstra <wesley@sifive.com> > > > > > > [Atish: Compatible string update] > > > > > > Signed-off-by: Atish Patra <atish.patra@wdc.com> > > > > > > Signed-off-by: Yash Shah <yash.shah@sifive.com> > > > > > > --- > > > > > > .../devicetree/bindings/pwm/pwm-sifive.txt | 33 ++++++++++++++++++++++ > > > > > > 1 file changed, 33 insertions(+) > > > > > > create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > new file mode 100644 > > > > > > index 0000000..8dcb40d > > > > > > --- /dev/null > > > > > > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > @@ -0,0 +1,33 @@ > > > > > > +SiFive PWM controller > > > > > > + > > > > > > +Unlike most other PWM controllers, the SiFive PWM controller currently only > > > > > > +supports one period for all channels in the PWM. This is set globally in DTS. > > > > > > > > > > You can simply drop this if the first user can set this using the usual > > > > > interface. Don't you like this suggestion that I already made a few > > > > > times now? > > > > > > > > > > Did you consider to make the driver support only a single output with a > > > > > more flexible period setting? > > > > > > > > We cannot consider supporting only single output since we have boards that > > > > use the additional PWM channels to control individual LED brightness > > > > of a tri-color LED. > > > > If we go down to one channel, then we can't control the brightness of > > > > the individual LEDs. > > > > It will break the use case. > > > > > > OK. > > > > > > > I am considering the below approach, let me know if it's fine by you. > > > > > > > > - Drop the global period property and allow the only first user to change period > > > > using the usual interface. > > > > - A note in the binding that all PWMs need to run at the same > > > > period. If the driver already refuses to apply incompatible periods, > > > > the users are going to notice that they've got the DT wrong. > > > > - In driver code, count the users using the .request and .free callbacks. > > > > Based on this, allow changes to period iff the user count is one. > > > > > > Not sure you need to point this limitation in the binding doc. Other > > > than that this is fine. > > > > I think it's useful to point this out in the binding documentation since > > it's something that device tree writers will want to know. > > OK, we're talking about an FPGA implementation but I still think if the > dt-author is the first to know about this limitation this is too late. > The hardware designer must know about that, and they don't look into the > bindind documentation. The binding documentation should IMHO only > describe the binding and functional limitiations of the device are out > of scope. > > The binding for the Freescale network interface doesn't describe that it > only supports 480 MBit/s in its GHz mode, and that's good. The binding > for i2c devices doesn't describe that a reboot in the middle of a > transfer might block the bus. > > The target for the binding documentation is to document how a given > device is described in a device tree. It's not there to duplicate > information that belongs in the reference manual. But the device tree bindings for PWM devices describe where and how to describe the period for each PWM that you reference. That's entirely different from the examples that you give above. The generic PWM documentation implies that the period can be set per PWM channel, so explicitly pointing out in the bindings for a specific controller that this is *not* the case is a good thing. And really, it's not like we're quoting pages and pages from technical reference documentation. This is just a single sentence in a very short document. Surely that's not going to hurt anyone. Thierry
On Wed, Feb 06, 2019 at 05:16:34PM +0100, Thierry Reding wrote: > On Wed, Feb 06, 2019 at 04:38:54PM +0100, Uwe Kleine-König wrote: > > On Wed, Feb 06, 2019 at 01:40:55PM +0100, Thierry Reding wrote: > > > On Wed, Feb 06, 2019 at 12:07:30PM +0100, Uwe Kleine-König wrote: > > > > On Wed, Feb 06, 2019 at 04:18:47PM +0530, Yash Shah wrote: > > > > > On Wed, Jan 30, 2019 at 1:44 PM Uwe Kleine-König > > > > > <u.kleine-koenig@pengutronix.de> wrote: > > > > > > > > > > > > On Tue, Jan 29, 2019 at 05:13:18PM +0530, Yash Shah wrote: > > > > > > > DT documentation for PWM controller added. > > > > > > > > > > > > > > Signed-off-by: Wesley W. Terpstra <wesley@sifive.com> > > > > > > > [Atish: Compatible string update] > > > > > > > Signed-off-by: Atish Patra <atish.patra@wdc.com> > > > > > > > Signed-off-by: Yash Shah <yash.shah@sifive.com> > > > > > > > --- > > > > > > > .../devicetree/bindings/pwm/pwm-sifive.txt | 33 ++++++++++++++++++++++ > > > > > > > 1 file changed, 33 insertions(+) > > > > > > > create mode 100644 Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > > > > > > > > > diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > > new file mode 100644 > > > > > > > index 0000000..8dcb40d > > > > > > > --- /dev/null > > > > > > > +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt > > > > > > > @@ -0,0 +1,33 @@ > > > > > > > +SiFive PWM controller > > > > > > > + > > > > > > > +Unlike most other PWM controllers, the SiFive PWM controller currently only > > > > > > > +supports one period for all channels in the PWM. This is set globally in DTS. > > > > > > > > > > > > You can simply drop this if the first user can set this using the usual > > > > > > interface. Don't you like this suggestion that I already made a few > > > > > > times now? > > > > > > > > > > > > Did you consider to make the driver support only a single output with a > > > > > > more flexible period setting? > > > > > > > > > > We cannot consider supporting only single output since we have boards that > > > > > use the additional PWM channels to control individual LED brightness > > > > > of a tri-color LED. > > > > > If we go down to one channel, then we can't control the brightness of > > > > > the individual LEDs. > > > > > It will break the use case. > > > > > > > > OK. > > > > > > > > > I am considering the below approach, let me know if it's fine by you. > > > > > > > > > > - Drop the global period property and allow the only first user to change period > > > > > using the usual interface. > > > > > - A note in the binding that all PWMs need to run at the same > > > > > period. If the driver already refuses to apply incompatible periods, > > > > > the users are going to notice that they've got the DT wrong. > > > > > - In driver code, count the users using the .request and .free callbacks. > > > > > Based on this, allow changes to period iff the user count is one. > > > > > > > > Not sure you need to point this limitation in the binding doc. Other > > > > than that this is fine. > > > > > > I think it's useful to point this out in the binding documentation since > > > it's something that device tree writers will want to know. > > > > OK, we're talking about an FPGA implementation but I still think if the > > dt-author is the first to know about this limitation this is too late. > > The hardware designer must know about that, and they don't look into the > > bindind documentation. The binding documentation should IMHO only > > describe the binding and functional limitiations of the device are out > > of scope. > > > > The binding for the Freescale network interface doesn't describe that it > > only supports 480 MBit/s in its GHz mode, and that's good. The binding > > for i2c devices doesn't describe that a reboot in the middle of a > > transfer might block the bus. > > > > The target for the binding documentation is to document how a given > > device is described in a device tree. It's not there to duplicate > > information that belongs in the reference manual. > > But the device tree bindings for PWM devices describe where and how to > describe the period for each PWM that you reference. That's entirely > different from the examples that you give above. Ah right, I had not on my radar that the binding also gives a suggestion for the period. Then yes, I agree that pointing out that all pwms belonging to the same provider should have matching periods is a good idea. Is using this "typical" approach to specify the period in a pwm-list a bad idea for this device type for this reason? On the other hand diverting from the typical approach has its own cost. Not sure ... Best regards Uwe
diff --git a/Documentation/devicetree/bindings/pwm/pwm-sifive.txt b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt new file mode 100644 index 0000000..8dcb40d --- /dev/null +++ b/Documentation/devicetree/bindings/pwm/pwm-sifive.txt @@ -0,0 +1,33 @@ +SiFive PWM controller + +Unlike most other PWM controllers, the SiFive PWM controller currently only +supports one period for all channels in the PWM. This is set globally in DTS. +The period also has significant restrictions on the values it can achieve, +which the driver rounds to the nearest achievable frequency. +PWM RTL that corresponds to the IP block version numbers can be found +here: + +https://github.com/sifive/sifive-blocks/tree/master/src/main/scala/devices/pwm + +Required properties: +- compatible: Should be "sifive,$socname-pwm" and "sifive,pwmX". + Please refer to sifive-blocks-ip-versioning.txt for details. +- reg: physical base address and length of the controller's registers +- clocks: Should contain a clock identifier for the PWM's parent clock. +- #pwm-cells: Should be 2. + The first cell is the PWM channel number + The second cell is the PWM polarity +- sifive,period-ns: the driver will get as close to this period as it can +- interrupts: one interrupt per PWM channel + +Examples: + +pwm: pwm@10020000 { + compatible = "sifive,fu540-c000-pwm", "sifive,pwm0"; + reg = <0x0 0x10020000 0x0 0x1000>; + clocks = <&tlclk>; + interrupt-parent = <&plic>; + interrupts = <42 43 44 45>; + #pwm-cells = <2>; + sifive,period-ns = <1000000>; +};