| Message ID | 1424276101-30137-5-git-send-email-lee.jones@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
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On Wed, Feb 18, 2015 at 10:15 AM, Lee Jones <lee.jones@linaro.org> wrote: > Signed-off-by: Lee Jones <lee.jones@linaro.org> > --- > .../devicetree/bindings/clock/clk-domain.txt | 35 ++++++++++++++++++++++ > 1 file changed, 35 insertions(+) > create mode 100644 Documentation/devicetree/bindings/clock/clk-domain.txt > > diff --git a/Documentation/devicetree/bindings/clock/clk-domain.txt b/Documentation/devicetree/bindings/clock/clk-domain.txt > new file mode 100644 > index 0000000..b86772f5 > --- /dev/null > +++ b/Documentation/devicetree/bindings/clock/clk-domain.txt > @@ -0,0 +1,35 @@ > +Always-on Clock Domain > + > +Some hardware is contains bunches of clocks which must never be > +turned off. If drivers a) fail to obtain a reference to any of > +these or b) give up a previously obtained reference during suspend, > +the common clk framework will attempt to disable them and the > +hardware can fail irrecoverably. Usually, the only way to recover > +from these failures is to restart. How is (b) not a bug? While I think we need something here, I worry that this will be abused to be a list of clocks you have not gotten around to managing. We cannot be changing the DT every time the kernel starts managing a clock. I think this should operate more as always on until claimed. But then you get into drivers having to be aware that the clock started enabled. Also, I feel like we are using DT to work around kernel policy (of turning off clocks). If the policy was to leave on clocks, then we would be trying to put a list of clocks to disable in DT. Rob > + > +To avoid either of these two scenarios from catastrophically > +disabling an otherwise perfectly healthy running system, we have > +implemented a clock domain where clocks are consumed and references > +are taken, thus preventing them from being shut down by the > +framework. > + > +We use the generic clock bindings found in: > + Documentation/devicetree/bindings/clock/clock-bindings.txt > + > +Required properties: > +- compatible : Must be "always-on-clk-domain" > + > +Example: > + > +clk-domain { > + compatible = "always-on-clk-domain"; > + clocks = <&clk_s_c0_flexgen CLK_EXT2F_A9>, > + <&clk_s_c0_flexgen CLK_COMPO_DVP>, > + <&clk_s_c0_flexgen CLK_MMC_1>, > + <&clk_s_c0_flexgen CLK_ICN_SBC>, > + <&clk_s_c0_flexgen CLK_ICN_LMI>, > + <&clk_s_c0_flexgen CLK_ICN_CPU>, > + <&clk_s_c0_flexgen CLK_TX_ICN_DMU>, > + <&clk_s_a0_flexgen CLK_IC_LMI0>, > + <&clk_m_a9>; > +}; > -- > 1.9.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Wed, 18 Feb 2015, Rob Herring wrote: > On Wed, Feb 18, 2015 at 10:15 AM, Lee Jones <lee.jones@linaro.org> wrote: > > Signed-off-by: Lee Jones <lee.jones@linaro.org> > > --- > > .../devicetree/bindings/clock/clk-domain.txt | 35 ++++++++++++++++++++++ > > 1 file changed, 35 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/clock/clk-domain.txt > > > > diff --git a/Documentation/devicetree/bindings/clock/clk-domain.txt b/Documentation/devicetree/bindings/clock/clk-domain.txt > > new file mode 100644 > > index 0000000..b86772f5 > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/clock/clk-domain.txt > > @@ -0,0 +1,35 @@ > > +Always-on Clock Domain > > + > > +Some hardware is contains bunches of clocks which must never be > > +turned off. If drivers a) fail to obtain a reference to any of > > +these or b) give up a previously obtained reference during suspend, > > +the common clk framework will attempt to disable them and the > > +hardware can fail irrecoverably. Usually, the only way to recover > > +from these failures is to restart. > > How is (b) not a bug? Clocks are normally disabled during suspend. When clocks are disabled they give up their reference. If references reach 0, the clock is gated. If one of these clocks is gated, the system will never come out of suspend. How is it a bug? > While I think we need something here, I worry that this will be abused > to be a list of clocks you have not gotten around to managing. We You can say that about any framework. It's our responsibility to ask the right questions and to disallow it from being abused. The clocks I use in the (real-world) example in this set are _really_ always-on. If any of them are turned off the system will cease to perform in any meaningful way. > cannot be changing the DT every time the kernel starts managing a > clock. I think this should operate more as always on until claimed. The point of this is that even when these clocks are claimed, there is an issue that when unclaimed (i.e. during suspend) the clk framework will attempt to gate them, and when they do *boom*. > But then you get into drivers having to be aware that the clock > started enabled. This has nothing to do with the initial state of the clock. It's whether the clock is integral (i.e. is part of a vital interconnect) that's important. For instance, ST's bootloader turns on lots of clocks which can be safely gated if unused. The clocks we're registering with this always-on framework cannot. > Also, I feel like we are using DT to work around kernel policy (of > turning off clocks). If the policy was to leave on clocks, then we > would be trying to put a list of clocks to disable in DT. I'm not sure I understand your point. The current policy is correct if it's power that you care about, which is invariably the point of disabling clocks in the first place, right? Also, this has nothing to do with DT per say. It's just another framework driver. > > +To avoid either of these two scenarios from catastrophically > > +disabling an otherwise perfectly healthy running system, we have > > +implemented a clock domain where clocks are consumed and references > > +are taken, thus preventing them from being shut down by the > > +framework. > > + > > +We use the generic clock bindings found in: > > + Documentation/devicetree/bindings/clock/clock-bindings.txt > > + > > +Required properties: > > +- compatible : Must be "always-on-clk-domain" > > + > > +Example: > > + > > +clk-domain { > > + compatible = "always-on-clk-domain"; > > + clocks = <&clk_s_c0_flexgen CLK_EXT2F_A9>, > > + <&clk_s_c0_flexgen CLK_COMPO_DVP>, > > + <&clk_s_c0_flexgen CLK_MMC_1>, > > + <&clk_s_c0_flexgen CLK_ICN_SBC>, > > + <&clk_s_c0_flexgen CLK_ICN_LMI>, > > + <&clk_s_c0_flexgen CLK_ICN_CPU>, > > + <&clk_s_c0_flexgen CLK_TX_ICN_DMU>, > > + <&clk_s_a0_flexgen CLK_IC_LMI0>, > > + <&clk_m_a9>; > > +}; > > > > > > _______________________________________________ > > linux-arm-kernel mailing list > > linux-arm-kernel@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Wed, Feb 18, 2015 at 11:12 AM, Lee Jones <lee.jones@linaro.org> wrote: > On Wed, 18 Feb 2015, Rob Herring wrote: > >> On Wed, Feb 18, 2015 at 10:15 AM, Lee Jones <lee.jones@linaro.org> wrote: >> > Signed-off-by: Lee Jones <lee.jones@linaro.org> >> > --- >> > .../devicetree/bindings/clock/clk-domain.txt | 35 ++++++++++++++++++++++ >> > 1 file changed, 35 insertions(+) >> > create mode 100644 Documentation/devicetree/bindings/clock/clk-domain.txt >> > >> > diff --git a/Documentation/devicetree/bindings/clock/clk-domain.txt b/Documentation/devicetree/bindings/clock/clk-domain.txt >> > new file mode 100644 >> > index 0000000..b86772f5 >> > --- /dev/null >> > +++ b/Documentation/devicetree/bindings/clock/clk-domain.txt >> > @@ -0,0 +1,35 @@ >> > +Always-on Clock Domain >> > + >> > +Some hardware is contains bunches of clocks which must never be >> > +turned off. If drivers a) fail to obtain a reference to any of >> > +these or b) give up a previously obtained reference during suspend, >> > +the common clk framework will attempt to disable them and the >> > +hardware can fail irrecoverably. Usually, the only way to recover >> > +from these failures is to restart. >> >> How is (b) not a bug? > > Clocks are normally disabled during suspend. When clocks are disabled > they give up their reference. If references reach 0, the clock is > gated. If one of these clocks is gated, the system will never come > out of suspend. > > How is it a bug? It a clock needs to be enabled during suspend, then the driver using it should not disable it. Anyway, suspend is a bit orthogonal to this issue. >> While I think we need something here, I worry that this will be abused >> to be a list of clocks you have not gotten around to managing. We > > You can say that about any framework. It's our responsibility to ask > the right questions and to disallow it from being abused. The clocks > I use in the (real-world) example in this set are _really_ always-on. > If any of them are turned off the system will cease to perform in any > meaningful way. You cannot tell here up front whether clocks are really always-on. A reviewer is not going to know, and the submitter may not even have all the documentation and know the answer. Getting it wrong here means you have to change the dtb to fix it. Granted, it doesn't really break things in this case. >> cannot be changing the DT every time the kernel starts managing a >> clock. I think this should operate more as always on until claimed. > > The point of this is that even when these clocks are claimed, there is > an issue that when unclaimed (i.e. during suspend) the clk framework > will attempt to gate them, and when they do *boom*. > >> But then you get into drivers having to be aware that the clock >> started enabled. > > This has nothing to do with the initial state of the clock. It's > whether the clock is integral (i.e. is part of a vital interconnect) > that's important. For instance, ST's bootloader turns on lots of > clocks which can be safely gated if unused. The clocks we're > registering with this always-on framework cannot. It does because you have to assume either the initial state is wrong and you need to disable it, or that the initial state is correct and you need to leave the clock enabled. There are also other usecases such as simplefb where you want to leave clocks on until the real fb driver takes over. Consoles have a similar issue. Perhaps you need to model your buses more completely? Does simple-pm-bus help you? >> Also, I feel like we are using DT to work around kernel policy (of >> turning off clocks). If the policy was to leave on clocks, then we >> would be trying to put a list of clocks to disable in DT. > > I'm not sure I understand your point. The current policy is correct > if it's power that you care about, which is invariably the point of > disabling clocks in the first place, right? Also, this has nothing to > do with DT per say. It's just another framework driver. It does have something to do with DT because you are designing a binding around what the kernel does. Should the kernel assume it can disable clocks safely? Another OS may do the opposite and assume it cannot turn-off unused clocks. Then you would have a list of clocks safe to disable in DT. This is also completely solvable within the framework driver by claiming those clocks in the clock controller driver. Rob
On Wed, 18 Feb 2015, Rob Herring wrote: > On Wed, Feb 18, 2015 at 11:12 AM, Lee Jones <lee.jones@linaro.org> wrote: > > On Wed, 18 Feb 2015, Rob Herring wrote: > > > >> On Wed, Feb 18, 2015 at 10:15 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> > Signed-off-by: Lee Jones <lee.jones@linaro.org> > >> > --- > >> > .../devicetree/bindings/clock/clk-domain.txt | 35 ++++++++++++++++++++++ > >> > 1 file changed, 35 insertions(+) > >> > create mode 100644 Documentation/devicetree/bindings/clock/clk-domain.txt > >> > > >> > diff --git a/Documentation/devicetree/bindings/clock/clk-domain.txt b/Documentation/devicetree/bindings/clock/clk-domain.txt > >> > new file mode 100644 > >> > index 0000000..b86772f5 > >> > --- /dev/null > >> > +++ b/Documentation/devicetree/bindings/clock/clk-domain.txt > >> > @@ -0,0 +1,35 @@ > >> > +Always-on Clock Domain > >> > + > >> > +Some hardware is contains bunches of clocks which must never be > >> > +turned off. If drivers a) fail to obtain a reference to any of > >> > +these or b) give up a previously obtained reference during suspend, > >> > +the common clk framework will attempt to disable them and the > >> > +hardware can fail irrecoverably. Usually, the only way to recover > >> > +from these failures is to restart. > >> > >> How is (b) not a bug? > > > > Clocks are normally disabled during suspend. When clocks are disabled > > they give up their reference. If references reach 0, the clock is > > gated. If one of these clocks is gated, the system will never come > > out of suspend. > > > > How is it a bug? > > It a clock needs to be enabled during suspend, then the driver using > it should not disable it. Anyway, suspend is a bit orthogonal to this > issue. IMO, it's not the driver's responsibility to know which clock they are using and whether it's a critical clock or not. > >> While I think we need something here, I worry that this will be abused > >> to be a list of clocks you have not gotten around to managing. We > > > > You can say that about any framework. It's our responsibility to ask > > the right questions and to disallow it from being abused. The clocks > > I use in the (real-world) example in this set are _really_ always-on. > > If any of them are turned off the system will cease to perform in any > > meaningful way. > > You cannot tell here up front whether clocks are really always-on. A > reviewer is not going to know, and the submitter may not even have all > the documentation and know the answer. Getting it wrong here means you > have to change the dtb to fix it. Granted, it doesn't really break > things in this case. We should make it clear in the documentation that this framework should only be used if the clock is a critical "if it's turned off it will cripple the system" one. > >> cannot be changing the DT every time the kernel starts managing a > >> clock. I think this should operate more as always on until claimed. > > > > The point of this is that even when these clocks are claimed, there is > > an issue that when unclaimed (i.e. during suspend) the clk framework > > will attempt to gate them, and when they do *boom*. > > > >> But then you get into drivers having to be aware that the clock > >> started enabled. > > > > This has nothing to do with the initial state of the clock. It's > > whether the clock is integral (i.e. is part of a vital interconnect) > > that's important. For instance, ST's bootloader turns on lots of > > clocks which can be safely gated if unused. The clocks we're > > registering with this always-on framework cannot. > > It does because you have to assume either the initial state is wrong > and you need to disable it, or that the initial state is correct and > you need to leave the clock enabled. I think the kernel's policy is a good one i.e. wait until all devices are probed and have had the opportunity to take the clocks they need, at which point we can usually safely gate the remainder. These types of clocks are the exception however; hence the need for this driver. There are other vendors which have similar issues with their h/w. These are currently using bespoke versions of this implementation, but IMO a generic solution would be better. > There are also other usecases such as simplefb where you want to leave > clocks on until the real fb driver takes over. Consoles have a similar > issue. Why wouldn't these devices have taken references by the time clk_disable_unused() is called? > Perhaps you need to model your buses more completely? Would you mind explaining this a little more please? > Does simple-pm-bus help you? I have no idea what this is, and I'm struggling to grep for it too? > >> Also, I feel like we are using DT to work around kernel policy (of > >> turning off clocks). If the policy was to leave on clocks, then we > >> would be trying to put a list of clocks to disable in DT. > > > > I'm not sure I understand your point. The current policy is correct > > if it's power that you care about, which is invariably the point of > > disabling clocks in the first place, right? Also, this has nothing to > > do with DT per say. It's just another framework driver. > > It does have something to do with DT because you are designing a > binding around what the kernel does. Should the kernel assume it can > disable clocks safely? I guess it depends on what you're trying to achieve. Personally I think the kernel's policy is a good one, especually with regards to power saving. What are you suggesting? A new policy? > Another OS may do the opposite and assume it > cannot turn-off unused clocks. Then you would have a list of clocks > safe to disable in DT. Sounds bananas. What's good about that kind of policy? It wouldn't matter anyway, both of these implementations can live harmoniously in the same tree. > This is also completely solvable within the framework driver by > claiming those clocks in the clock controller driver. This conversation has now gone full circle. This was an earlier suggestion, but it was considered hacky, and I'm inclined to agree. An always-on power domain was deemed to be a much more elegant solution.
On Wed, Feb 18, 2015 at 3:54 PM, Lee Jones <lee.jones@linaro.org> wrote: > On Wed, 18 Feb 2015, Rob Herring wrote: > >> On Wed, Feb 18, 2015 at 11:12 AM, Lee Jones <lee.jones@linaro.org> wrote: >> > On Wed, 18 Feb 2015, Rob Herring wrote: >> > >> >> On Wed, Feb 18, 2015 at 10:15 AM, Lee Jones <lee.jones@linaro.org> wrote: >> >> > Signed-off-by: Lee Jones <lee.jones@linaro.org> >> >> > --- >> >> > .../devicetree/bindings/clock/clk-domain.txt | 35 ++++++++++++++++++++++ >> >> > 1 file changed, 35 insertions(+) >> >> > create mode 100644 Documentation/devicetree/bindings/clock/clk-domain.txt >> >> > >> >> > diff --git a/Documentation/devicetree/bindings/clock/clk-domain.txt b/Documentation/devicetree/bindings/clock/clk-domain.txt >> >> > new file mode 100644 >> >> > index 0000000..b86772f5 >> >> > --- /dev/null >> >> > +++ b/Documentation/devicetree/bindings/clock/clk-domain.txt >> >> > @@ -0,0 +1,35 @@ >> >> > +Always-on Clock Domain >> >> > + >> >> > +Some hardware is contains bunches of clocks which must never be >> >> > +turned off. If drivers a) fail to obtain a reference to any of >> >> > +these or b) give up a previously obtained reference during suspend, >> >> > +the common clk framework will attempt to disable them and the >> >> > +hardware can fail irrecoverably. Usually, the only way to recover >> >> > +from these failures is to restart. >> >> >> >> How is (b) not a bug? >> > >> > Clocks are normally disabled during suspend. When clocks are disabled >> > they give up their reference. If references reach 0, the clock is >> > gated. If one of these clocks is gated, the system will never come >> > out of suspend. >> > >> > How is it a bug? >> >> It a clock needs to be enabled during suspend, then the driver using >> it should not disable it. Anyway, suspend is a bit orthogonal to this >> issue. > > IMO, it's not the driver's responsibility to know which clock they are > using and whether it's a critical clock or not. Certainly drivers should not know about clocks outside of their h/w block, but they absolutely should know if a clock is needed for wake-up. >> >> While I think we need something here, I worry that this will be abused >> >> to be a list of clocks you have not gotten around to managing. We >> > >> > You can say that about any framework. It's our responsibility to ask >> > the right questions and to disallow it from being abused. The clocks >> > I use in the (real-world) example in this set are _really_ always-on. >> > If any of them are turned off the system will cease to perform in any >> > meaningful way. >> >> You cannot tell here up front whether clocks are really always-on. A >> reviewer is not going to know, and the submitter may not even have all >> the documentation and know the answer. Getting it wrong here means you >> have to change the dtb to fix it. Granted, it doesn't really break >> things in this case. > > We should make it clear in the documentation that this framework > should only be used if the clock is a critical "if it's turned off it > will cripple the system" one. > >> >> cannot be changing the DT every time the kernel starts managing a >> >> clock. I think this should operate more as always on until claimed. >> > >> > The point of this is that even when these clocks are claimed, there is >> > an issue that when unclaimed (i.e. during suspend) the clk framework >> > will attempt to gate them, and when they do *boom*. >> > >> >> But then you get into drivers having to be aware that the clock >> >> started enabled. >> > >> > This has nothing to do with the initial state of the clock. It's >> > whether the clock is integral (i.e. is part of a vital interconnect) >> > that's important. For instance, ST's bootloader turns on lots of >> > clocks which can be safely gated if unused. The clocks we're >> > registering with this always-on framework cannot. >> >> It does because you have to assume either the initial state is wrong >> and you need to disable it, or that the initial state is correct and >> you need to leave the clock enabled. > > I think the kernel's policy is a good one i.e. wait until all devices > are probed and have had the opportunity to take the clocks they need, > at which point we can usually safely gate the remainder. These types > of clocks are the exception however; hence the need for this driver. > There are other vendors which have similar issues with their h/w. > These are currently using bespoke versions of this implementation, but > IMO a generic solution would be better. > >> There are also other usecases such as simplefb where you want to leave >> clocks on until the real fb driver takes over. Consoles have a similar >> issue. > > Why wouldn't these devices have taken references by the time > clk_disable_unused() is called? Not if the drivers are modules. >> Perhaps you need to model your buses more completely? > > Would you mind explaining this a little more please? > >> Does simple-pm-bus help you? > > I have no idea what this is, and I'm struggling to grep for it too? http://lwn.net/Articles/632058/ I'm not saying this works as-is for you, but people are starting to add bus properties to buses. >> >> Also, I feel like we are using DT to work around kernel policy (of >> >> turning off clocks). If the policy was to leave on clocks, then we >> >> would be trying to put a list of clocks to disable in DT. >> > >> > I'm not sure I understand your point. The current policy is correct >> > if it's power that you care about, which is invariably the point of >> > disabling clocks in the first place, right? Also, this has nothing to >> > do with DT per say. It's just another framework driver. >> >> It does have something to do with DT because you are designing a >> binding around what the kernel does. Should the kernel assume it can >> disable clocks safely? > > I guess it depends on what you're trying to achieve. Personally I > think the kernel's policy is a good one, especually with regards to > power saving. What are you suggesting? A new policy? No. The binding just has to work no matter what the OS policy. >> Another OS may do the opposite and assume it >> cannot turn-off unused clocks. Then you would have a list of clocks >> safe to disable in DT. > > Sounds bananas. What's good about that kind of policy? It wouldn't > matter anyway, both of these implementations can live harmoniously in > the same tree. Your systems won't go *boom*. >> This is also completely solvable within the framework driver by >> claiming those clocks in the clock controller driver. > > This conversation has now gone full circle. This was an earlier > suggestion, but it was considered hacky, and I'm inclined to agree. The clock maintainer doesn't want hacks in the clock framework and the DT maintainer doesn't want them in DT... We should put them in MFD. ;) > An always-on power domain was deemed to be a much more elegant > solution. Now you are mixing in power domains? I'm not saying we can't put something in DT. I'm okay with that, but it needs to handle the case of the clocks do get claimed either after boot (e.g. by a module) or in later kernels without a dtb change. Rob
Hi Lee, On Wed, Feb 18, 2015 at 10:54 PM, Lee Jones <lee.jones@linaro.org> wrote: >> >> > +Some hardware is contains bunches of clocks which must never be >> >> > +turned off. If drivers a) fail to obtain a reference to any of >> >> > +these or b) give up a previously obtained reference during suspend, >> >> > +the common clk framework will attempt to disable them and the >> >> > +hardware can fail irrecoverably. Usually, the only way to recover >> >> > +from these failures is to restart. >> >> >> >> How is (b) not a bug? >> > >> > Clocks are normally disabled during suspend. When clocks are disabled >> > they give up their reference. If references reach 0, the clock is >> > gated. If one of these clocks is gated, the system will never come >> > out of suspend. >> > >> > How is it a bug? >> >> It a clock needs to be enabled during suspend, then the driver using >> it should not disable it. Anyway, suspend is a bit orthogonal to this >> issue. > > IMO, it's not the driver's responsibility to know which clock they are > using and whether it's a critical clock or not. So it's (partly) a platform/bus issue. >> >> While I think we need something here, I worry that this will be abused >> >> to be a list of clocks you have not gotten around to managing. We >> > >> > You can say that about any framework. It's our responsibility to ask >> > the right questions and to disallow it from being abused. The clocks >> > I use in the (real-world) example in this set are _really_ always-on. >> > If any of them are turned off the system will cease to perform in any >> > meaningful way. >> >> You cannot tell here up front whether clocks are really always-on. A >> reviewer is not going to know, and the submitter may not even have all >> the documentation and know the answer. Getting it wrong here means you >> have to change the dtb to fix it. Granted, it doesn't really break >> things in this case. > > We should make it clear in the documentation that this framework > should only be used if the clock is a critical "if it's turned off it > will cripple the system" one. [...] > I think the kernel's policy is a good one i.e. wait until all devices > are probed and have had the opportunity to take the clocks they need, > at which point we can usually safely gate the remainder. These types > of clocks are the exception however; hence the need for this driver. > There are other vendors which have similar issues with their h/w. > These are currently using bespoke versions of this implementation, but > IMO a generic solution would be better. What kind of clocks are these? What do they control? Memory controllers? Bus controllers? They must control some device(s), so there should be one or more device nodes in DT that reference these clocks. As soon as that information is in DT, support can be added to Linux to make sure the "critical" clocks stay enabled, either through a real driver, or through platform code. >> Does simple-pm-bus help you? > > I have no idea what this is, and I'm struggling to grep for it too? Rob already provided a pointer. If you have more questions, feel free to ask! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > On Wed, Feb 18, 2015 at 10:54 PM, Lee Jones <lee.jones@linaro.org> wrote: > >> >> > +Some hardware is contains bunches of clocks which must never be > >> >> > +turned off. If drivers a) fail to obtain a reference to any of > >> >> > +these or b) give up a previously obtained reference during suspend, > >> >> > +the common clk framework will attempt to disable them and the > >> >> > +hardware can fail irrecoverably. Usually, the only way to recover > >> >> > +from these failures is to restart. > >> >> > >> >> How is (b) not a bug? > >> > > >> > Clocks are normally disabled during suspend. When clocks are disabled > >> > they give up their reference. If references reach 0, the clock is > >> > gated. If one of these clocks is gated, the system will never come > >> > out of suspend. > >> > > >> > How is it a bug? > >> > >> It a clock needs to be enabled during suspend, then the driver using > >> it should not disable it. Anyway, suspend is a bit orthogonal to this > >> issue. > > > > IMO, it's not the driver's responsibility to know which clock they are > > using and whether it's a critical clock or not. > > So it's (partly) a platform/bus issue. > > >> >> While I think we need something here, I worry that this will be abused > >> >> to be a list of clocks you have not gotten around to managing. We > >> > > >> > You can say that about any framework. It's our responsibility to ask > >> > the right questions and to disallow it from being abused. The clocks > >> > I use in the (real-world) example in this set are _really_ always-on. > >> > If any of them are turned off the system will cease to perform in any > >> > meaningful way. > >> > >> You cannot tell here up front whether clocks are really always-on. A > >> reviewer is not going to know, and the submitter may not even have all > >> the documentation and know the answer. Getting it wrong here means you > >> have to change the dtb to fix it. Granted, it doesn't really break > >> things in this case. > > > > We should make it clear in the documentation that this framework > > should only be used if the clock is a critical "if it's turned off it > > will cripple the system" one. > > [...] > > > I think the kernel's policy is a good one i.e. wait until all devices > > are probed and have had the opportunity to take the clocks they need, > > at which point we can usually safely gate the remainder. These types > > of clocks are the exception however; hence the need for this driver. > > There are other vendors which have similar issues with their h/w. > > These are currently using bespoke versions of this implementation, but > > IMO a generic solution would be better. > > What kind of clocks are these? What do they control? > Memory controllers? Bus controllers? > > They must control some device(s), so there should be one or more device > nodes in DT that reference these clocks. > As soon as that information is in DT, support can be added to Linux to > make sure the "critical" clocks stay enabled, either through a real driver, > or through platform code. Some do, some don't. For instance, we have one clock which controls SPI and I2C that must not be turned off. We discovered this then when a suspend was attempted and the board refused to resume. This clock also runs one of the critical interconnects that runs from the a9. It would be wrong to remove the clk_disable() attempt from the SPI/I2C drivers because the same IP on another board might be controlled by a different clock which is able to be gated. There are also clocks which control other interconnects that are not connected to any device drivers. If we fail to take references for them before clk_disable_unused() is called, again the board hangs. We even lose JTAG support. > >> Does simple-pm-bus help you? > > > > I have no idea what this is, and I'm struggling to grep for it too? > > Rob already provided a pointer. > If you have more questions, feel free to ask!
Hi Lee, On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@linaro.org> wrote: >> What kind of clocks are these? What do they control? >> Memory controllers? Bus controllers? >> >> They must control some device(s), so there should be one or more device >> nodes in DT that reference these clocks. >> As soon as that information is in DT, support can be added to Linux to >> make sure the "critical" clocks stay enabled, either through a real driver, >> or through platform code. > > Some do, some don't. For instance, we have one clock which controls > SPI and I2C that must not be turned off. We discovered this then when > a suspend was attempted and the board refused to resume. This clock > also runs one of the critical interconnects that runs from the a9. It > would be wrong to remove the clk_disable() attempt from the SPI/I2C > drivers because the same IP on another board might be controlled by a > different clock which is able to be gated. > > There are also clocks which control other interconnects that are not > connected to any device drivers. If we fail to take references for > them before clk_disable_unused() is called, again the board hangs. We > even lose JTAG support. Interconnects are buses. Can't you represent those buses in the DT hierarchy, and give them clocks properties? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
On Wed, 18 Feb 2015, Rob Herring wrote: > On Wed, Feb 18, 2015 at 3:54 PM, Lee Jones <lee.jones@linaro.org> wrote: > > On Wed, 18 Feb 2015, Rob Herring wrote: > > > >> On Wed, Feb 18, 2015 at 11:12 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> > On Wed, 18 Feb 2015, Rob Herring wrote: > >> > > >> >> On Wed, Feb 18, 2015 at 10:15 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> >> > Signed-off-by: Lee Jones <lee.jones@linaro.org> > >> >> > --- > >> >> > .../devicetree/bindings/clock/clk-domain.txt | 35 ++++++++++++++++++++++ > >> >> > 1 file changed, 35 insertions(+) > >> >> > create mode 100644 Documentation/devicetree/bindings/clock/clk-domain.txt > >> >> > > >> >> > diff --git a/Documentation/devicetree/bindings/clock/clk-domain.txt b/Documentation/devicetree/bindings/clock/clk-domain.txt > >> >> > new file mode 100644 > >> >> > index 0000000..b86772f5 > >> >> > --- /dev/null > >> >> > +++ b/Documentation/devicetree/bindings/clock/clk-domain.txt > >> >> > @@ -0,0 +1,35 @@ > >> >> > +Always-on Clock Domain > >> >> > + > >> >> > +Some hardware is contains bunches of clocks which must never be > >> >> > +turned off. If drivers a) fail to obtain a reference to any of > >> >> > +these or b) give up a previously obtained reference during suspend, > >> >> > +the common clk framework will attempt to disable them and the > >> >> > +hardware can fail irrecoverably. Usually, the only way to recover > >> >> > +from these failures is to restart. > >> >> > >> >> How is (b) not a bug? > >> > > >> > Clocks are normally disabled during suspend. When clocks are disabled > >> > they give up their reference. If references reach 0, the clock is > >> > gated. If one of these clocks is gated, the system will never come > >> > out of suspend. > >> > > >> > How is it a bug? > >> > >> It a clock needs to be enabled during suspend, then the driver using > >> it should not disable it. Anyway, suspend is a bit orthogonal to this > >> issue. > > > > IMO, it's not the driver's responsibility to know which clock they are > > using and whether it's a critical clock or not. > > Certainly drivers should not know about clocks outside of their h/w > block, but they absolutely should know if a clock is needed for > wake-up. > > >> >> While I think we need something here, I worry that this will be abused > >> >> to be a list of clocks you have not gotten around to managing. We > >> > > >> > You can say that about any framework. It's our responsibility to ask > >> > the right questions and to disallow it from being abused. The clocks > >> > I use in the (real-world) example in this set are _really_ always-on. > >> > If any of them are turned off the system will cease to perform in any > >> > meaningful way. > >> > >> You cannot tell here up front whether clocks are really always-on. A > >> reviewer is not going to know, and the submitter may not even have all > >> the documentation and know the answer. Getting it wrong here means you > >> have to change the dtb to fix it. Granted, it doesn't really break > >> things in this case. > > > > We should make it clear in the documentation that this framework > > should only be used if the clock is a critical "if it's turned off it > > will cripple the system" one. > > > >> >> cannot be changing the DT every time the kernel starts managing a > >> >> clock. I think this should operate more as always on until claimed. > >> > > >> > The point of this is that even when these clocks are claimed, there is > >> > an issue that when unclaimed (i.e. during suspend) the clk framework > >> > will attempt to gate them, and when they do *boom*. > >> > > >> >> But then you get into drivers having to be aware that the clock > >> >> started enabled. > >> > > >> > This has nothing to do with the initial state of the clock. It's > >> > whether the clock is integral (i.e. is part of a vital interconnect) > >> > that's important. For instance, ST's bootloader turns on lots of > >> > clocks which can be safely gated if unused. The clocks we're > >> > registering with this always-on framework cannot. > >> > >> It does because you have to assume either the initial state is wrong > >> and you need to disable it, or that the initial state is correct and > >> you need to leave the clock enabled. > > > > I think the kernel's policy is a good one i.e. wait until all devices > > are probed and have had the opportunity to take the clocks they need, > > at which point we can usually safely gate the remainder. These types > > of clocks are the exception however; hence the need for this driver. > > There are other vendors which have similar issues with their h/w. > > These are currently using bespoke versions of this implementation, but > > IMO a generic solution would be better. > > > >> There are also other usecases such as simplefb where you want to leave > >> clocks on until the real fb driver takes over. Consoles have a similar > >> issue. > > > > Why wouldn't these devices have taken references by the time > > clk_disable_unused() is called? > > Not if the drivers are modules. Can you rightfully compile the drivers for your monitor and serial console as modules and expect them to work until you load them? > >> Perhaps you need to model your buses more completely? > > > > Would you mind explaining this a little more please? > > > >> Does simple-pm-bus help you? > > > > I have no idea what this is, and I'm struggling to grep for it too? > > http://lwn.net/Articles/632058/ > > I'm not saying this works as-is for you, but people are starting to > add bus properties to buses. I'm struggling to see how this might help. Which node would you probe as simple-pm-bus? It sounds like a very bloated and convoluted way of saying "don't gate these clocks". Besides, isn't this the opposite what what we're trying to achieve? We don't want to enable any PM on these clocks, let along runtime PM. FYI, I also looked into genpd, but came to the same set of conclusions. > >> >> Also, I feel like we are using DT to work around kernel policy (of > >> >> turning off clocks). If the policy was to leave on clocks, then we > >> >> would be trying to put a list of clocks to disable in DT. > >> > > >> > I'm not sure I understand your point. The current policy is correct > >> > if it's power that you care about, which is invariably the point of > >> > disabling clocks in the first place, right? Also, this has nothing to > >> > do with DT per say. It's just another framework driver. > >> > >> It does have something to do with DT because you are designing a > >> binding around what the kernel does. Should the kernel assume it can > >> disable clocks safely? > > > > I guess it depends on what you're trying to achieve. Personally I > > think the kernel's policy is a good one, especually with regards to > > power saving. What are you suggesting? A new policy? > > No. The binding just has to work no matter what the OS policy. > > >> Another OS may do the opposite and assume it > >> cannot turn-off unused clocks. Then you would have a list of clocks > >> safe to disable in DT. > > > > Sounds bananas. What's good about that kind of policy? It wouldn't > > matter anyway, both of these implementations can live harmoniously in > > the same tree. > > Your systems won't go *boom*. > > >> This is also completely solvable within the framework driver by > >> claiming those clocks in the clock controller driver. > > > > This conversation has now gone full circle. This was an earlier > > suggestion, but it was considered hacky, and I'm inclined to agree. > > The clock maintainer doesn't want hacks in the clock framework and the > DT maintainer doesn't want them in DT... We should put them in MFD. ;) > > > An always-on power domain was deemed to be a much more elegant > > solution. > > Now you are mixing in power domains? > > I'm not saying we can't put something in DT. I'm okay with that, but > it needs to handle the case of the clocks do get claimed either after > boot (e.g. by a module) or in later kernels without a dtb change. > > Rob
On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > Hi Lee, > > On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> What kind of clocks are these? What do they control? > >> Memory controllers? Bus controllers? > >> > >> They must control some device(s), so there should be one or more device > >> nodes in DT that reference these clocks. > >> As soon as that information is in DT, support can be added to Linux to > >> make sure the "critical" clocks stay enabled, either through a real driver, > >> or through platform code. > > > > Some do, some don't. For instance, we have one clock which controls > > SPI and I2C that must not be turned off. We discovered this then when > > a suspend was attempted and the board refused to resume. This clock > > also runs one of the critical interconnects that runs from the a9. It > > would be wrong to remove the clk_disable() attempt from the SPI/I2C > > drivers because the same IP on another board might be controlled by a > > different clock which is able to be gated. > > > > There are also clocks which control other interconnects that are not > > connected to any device drivers. If we fail to take references for > > them before clk_disable_unused() is called, again the board hangs. We > > even lose JTAG support. > > Interconnects are buses. Can't you represent those buses in the DT > hierarchy, and give them clocks properties? So instead of this nice succinct, simple, cover all bases (interconnects was just an example, there are bound to be others), generic framework, you are suggesting to write drivers for devices which other than "don't turn my clocks off", Linux can't actually see or control?
Hi Lee, On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones <lee.jones@linaro.org> wrote: > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: >> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@linaro.org> wrote: >> >> What kind of clocks are these? What do they control? >> >> Memory controllers? Bus controllers? >> >> >> >> They must control some device(s), so there should be one or more device >> >> nodes in DT that reference these clocks. >> >> As soon as that information is in DT, support can be added to Linux to >> >> make sure the "critical" clocks stay enabled, either through a real driver, >> >> or through platform code. >> > >> > Some do, some don't. For instance, we have one clock which controls >> > SPI and I2C that must not be turned off. We discovered this then when >> > a suspend was attempted and the board refused to resume. This clock >> > also runs one of the critical interconnects that runs from the a9. It >> > would be wrong to remove the clk_disable() attempt from the SPI/I2C >> > drivers because the same IP on another board might be controlled by a >> > different clock which is able to be gated. >> > >> > There are also clocks which control other interconnects that are not >> > connected to any device drivers. If we fail to take references for >> > them before clk_disable_unused() is called, again the board hangs. We >> > even lose JTAG support. >> >> Interconnects are buses. Can't you represent those buses in the DT >> hierarchy, and give them clocks properties? > > So instead of this nice succinct, simple, cover all bases > (interconnects was just an example, there are bound to be others), > generic framework, you are suggesting to write drivers for devices > which other than "don't turn my clocks off", Linux can't actually see > or control? DT describes the hardware, not behavior. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > Hi Lee, > > On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones <lee.jones@linaro.org> wrote: > > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > >> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> >> What kind of clocks are these? What do they control? > >> >> Memory controllers? Bus controllers? > >> >> > >> >> They must control some device(s), so there should be one or more device > >> >> nodes in DT that reference these clocks. > >> >> As soon as that information is in DT, support can be added to Linux to > >> >> make sure the "critical" clocks stay enabled, either through a real driver, > >> >> or through platform code. > >> > > >> > Some do, some don't. For instance, we have one clock which controls > >> > SPI and I2C that must not be turned off. We discovered this then when > >> > a suspend was attempted and the board refused to resume. This clock > >> > also runs one of the critical interconnects that runs from the a9. It > >> > would be wrong to remove the clk_disable() attempt from the SPI/I2C > >> > drivers because the same IP on another board might be controlled by a > >> > different clock which is able to be gated. > >> > > >> > There are also clocks which control other interconnects that are not > >> > connected to any device drivers. If we fail to take references for > >> > them before clk_disable_unused() is called, again the board hangs. We > >> > even lose JTAG support. > >> > >> Interconnects are buses. Can't you represent those buses in the DT > >> hierarchy, and give them clocks properties? > > > > So instead of this nice succinct, simple, cover all bases > > (interconnects was just an example, there are bound to be others), > > generic framework, you are suggesting to write drivers for devices > > which other than "don't turn my clocks off", Linux can't actually see > > or control? > > DT describes the hardware, not behavior. Okay so ... /* * ICNs are not visible/controllable in Linux, but references to their * clocks must be obtained and retained or the platform will become * irrecoverably unresponsive. */ interconnects@0 { compatible = "always-on-clk-domain"; clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>, <&clk_s_c0_flexgen CLK_ICN_LMI>, <&clk_s_c0_flexgen CLK_ICN_CPU>, <&clk_s_c0_flexgen CLK_TX_ICN_DMU>; };
Hi Lee, On Thu, Feb 19, 2015 at 11:28 AM, Lee Jones <lee.jones@linaro.org> wrote: > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: >> On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones <lee.jones@linaro.org> wrote: >> > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: >> >> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@linaro.org> wrote: >> >> >> What kind of clocks are these? What do they control? >> >> >> Memory controllers? Bus controllers? >> >> >> >> >> >> They must control some device(s), so there should be one or more device >> >> >> nodes in DT that reference these clocks. >> >> >> As soon as that information is in DT, support can be added to Linux to >> >> >> make sure the "critical" clocks stay enabled, either through a real driver, >> >> >> or through platform code. >> >> > >> >> > Some do, some don't. For instance, we have one clock which controls >> >> > SPI and I2C that must not be turned off. We discovered this then when >> >> > a suspend was attempted and the board refused to resume. This clock >> >> > also runs one of the critical interconnects that runs from the a9. It >> >> > would be wrong to remove the clk_disable() attempt from the SPI/I2C >> >> > drivers because the same IP on another board might be controlled by a >> >> > different clock which is able to be gated. >> >> > >> >> > There are also clocks which control other interconnects that are not >> >> > connected to any device drivers. If we fail to take references for >> >> > them before clk_disable_unused() is called, again the board hangs. We >> >> > even lose JTAG support. >> >> >> >> Interconnects are buses. Can't you represent those buses in the DT >> >> hierarchy, and give them clocks properties? >> > >> > So instead of this nice succinct, simple, cover all bases >> > (interconnects was just an example, there are bound to be others), >> > generic framework, you are suggesting to write drivers for devices >> > which other than "don't turn my clocks off", Linux can't actually see >> > or control? >> >> DT describes the hardware, not behavior. > > Okay so ... > > /* > * ICNs are not visible/controllable in Linux, but references to their > * clocks must be obtained and retained or the platform will become > * irrecoverably unresponsive. > */ > interconnects@0 { > compatible = "always-on-clk-domain"; st,...flexgen... > clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>, > <&clk_s_c0_flexgen CLK_ICN_LMI>, > <&clk_s_c0_flexgen CLK_ICN_CPU>, > <&clk_s_c0_flexgen CLK_TX_ICN_DMU>; > }; And then you can have platform code that binds against st,...flexgen..., and enables all referenced clocks. Alternatively, if you have power domains, you can add a reference to the power domain, and let the power domain driver handle it. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > Hi Lee, > > On Thu, Feb 19, 2015 at 11:28 AM, Lee Jones <lee.jones@linaro.org> wrote: > > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > >> On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > >> >> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> >> >> What kind of clocks are these? What do they control? > >> >> >> Memory controllers? Bus controllers? > >> >> >> > >> >> >> They must control some device(s), so there should be one or more device > >> >> >> nodes in DT that reference these clocks. > >> >> >> As soon as that information is in DT, support can be added to Linux to > >> >> >> make sure the "critical" clocks stay enabled, either through a real driver, > >> >> >> or through platform code. > >> >> > > >> >> > Some do, some don't. For instance, we have one clock which controls > >> >> > SPI and I2C that must not be turned off. We discovered this then when > >> >> > a suspend was attempted and the board refused to resume. This clock > >> >> > also runs one of the critical interconnects that runs from the a9. It > >> >> > would be wrong to remove the clk_disable() attempt from the SPI/I2C > >> >> > drivers because the same IP on another board might be controlled by a > >> >> > different clock which is able to be gated. > >> >> > > >> >> > There are also clocks which control other interconnects that are not > >> >> > connected to any device drivers. If we fail to take references for > >> >> > them before clk_disable_unused() is called, again the board hangs. We > >> >> > even lose JTAG support. > >> >> > >> >> Interconnects are buses. Can't you represent those buses in the DT > >> >> hierarchy, and give them clocks properties? > >> > > >> > So instead of this nice succinct, simple, cover all bases > >> > (interconnects was just an example, there are bound to be others), > >> > generic framework, you are suggesting to write drivers for devices > >> > which other than "don't turn my clocks off", Linux can't actually see > >> > or control? > >> > >> DT describes the hardware, not behavior. > > > > Okay so ... > > > > /* > > * ICNs are not visible/controllable in Linux, but references to their > > * clocks must be obtained and retained or the platform will become > > * irrecoverably unresponsive. > > */ > > interconnects@0 { > > compatible = "always-on-clk-domain"; > > st,...flexgen... > > > clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>, > > <&clk_s_c0_flexgen CLK_ICN_LMI>, > > <&clk_s_c0_flexgen CLK_ICN_CPU>, > > <&clk_s_c0_flexgen CLK_TX_ICN_DMU>; > > }; > > And then you can have platform code that binds against st,...flexgen..., > and enables all referenced clocks. Flexgen isn't a device, it's a clk source. a) writing a device driver for a clk source seems wrong b) what if on another platform a different clock source supplied the clock? Write another driver? And what if the ICNs are connected to different clock sources? More drivers? c) all of these drivers will only do one thing -- pull a reference and keep hold of it. You want 50 drivers (across all platforms) doing only that? Or, more sanely, do you want this one generic framework driver doing that? > Alternatively, if you have power domains, you can add a reference to > the power domain, and let the power domain driver handle it. I'm not sure what a power domain driver will do? We need a driver to _not_ give up references, that is all. :)
Hi Lee, On Thu, Feb 19, 2015 at 11:43 AM, Lee Jones <lee.jones@linaro.org> wrote: > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: >> On Thu, Feb 19, 2015 at 11:28 AM, Lee Jones <lee.jones@linaro.org> wrote: >> > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: >> >> On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones <lee.jones@linaro.org> wrote: >> >> > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: >> >> >> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@linaro.org> wrote: >> >> >> >> What kind of clocks are these? What do they control? >> >> >> >> Memory controllers? Bus controllers? >> >> >> >> >> >> >> >> They must control some device(s), so there should be one or more device >> >> >> >> nodes in DT that reference these clocks. >> >> >> >> As soon as that information is in DT, support can be added to Linux to >> >> >> >> make sure the "critical" clocks stay enabled, either through a real driver, >> >> >> >> or through platform code. >> >> >> > >> >> >> > Some do, some don't. For instance, we have one clock which controls >> >> >> > SPI and I2C that must not be turned off. We discovered this then when >> >> >> > a suspend was attempted and the board refused to resume. This clock >> >> >> > also runs one of the critical interconnects that runs from the a9. It >> >> >> > would be wrong to remove the clk_disable() attempt from the SPI/I2C >> >> >> > drivers because the same IP on another board might be controlled by a >> >> >> > different clock which is able to be gated. >> >> >> > >> >> >> > There are also clocks which control other interconnects that are not >> >> >> > connected to any device drivers. If we fail to take references for >> >> >> > them before clk_disable_unused() is called, again the board hangs. We >> >> >> > even lose JTAG support. >> >> >> >> >> >> Interconnects are buses. Can't you represent those buses in the DT >> >> >> hierarchy, and give them clocks properties? >> >> > >> >> > So instead of this nice succinct, simple, cover all bases >> >> > (interconnects was just an example, there are bound to be others), >> >> > generic framework, you are suggesting to write drivers for devices >> >> > which other than "don't turn my clocks off", Linux can't actually see >> >> > or control? >> >> >> >> DT describes the hardware, not behavior. >> > >> > Okay so ... >> > >> > /* >> > * ICNs are not visible/controllable in Linux, but references to their >> > * clocks must be obtained and retained or the platform will become >> > * irrecoverably unresponsive. >> > */ >> > interconnects@0 { >> > compatible = "always-on-clk-domain"; >> >> st,...flexgen... >> >> > clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>, >> > <&clk_s_c0_flexgen CLK_ICN_LMI>, >> > <&clk_s_c0_flexgen CLK_ICN_CPU>, >> > <&clk_s_c0_flexgen CLK_TX_ICN_DMU>; >> > }; >> >> And then you can have platform code that binds against st,...flexgen..., >> and enables all referenced clocks. > > Flexgen isn't a device, it's a clk source. a) writing a device driver Sorry, I'm not familiar with ST nomenclature. So that should become the name of the interconnect/bus. > for a clk source seems wrong b) what if on another platform a > different clock source supplied the clock? Write another driver? And > what if the ICNs are connected to different clock sources? More > drivers? c) all of these drivers will only do one thing -- pull a > reference and keep hold of it. You want 50 drivers (across all > platforms) doing only that? Or, more sanely, do you want this one > generic framework driver doing that? > >> Alternatively, if you have power domains, you can add a reference to >> the power domain, and let the power domain driver handle it. > > I'm not sure what a power domain driver will do? We need a driver to > _not_ give up references, that is all. :) A power domain driver can do anything it wants. That includes enabling your interconnect clocks, and keeping them enabled. Now, if flexgen is the name of the clock source, then all devices connected to flexgen are part of the flexgen clock domain, which can be represented in Linux using the generic PM domain. Do all devices connected to flexgen need to be handled similarly w.r.t. clocks? If yes, the genpd may be the place to implement that. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > On Thu, Feb 19, 2015 at 11:43 AM, Lee Jones <lee.jones@linaro.org> wrote: > > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > >> On Thu, Feb 19, 2015 at 11:28 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > >> >> On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> >> > On Thu, 19 Feb 2015, Geert Uytterhoeven wrote: > >> >> >> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@linaro.org> wrote: > >> >> >> >> What kind of clocks are these? What do they control? > >> >> >> >> Memory controllers? Bus controllers? > >> >> >> >> > >> >> >> >> They must control some device(s), so there should be one or more device > >> >> >> >> nodes in DT that reference these clocks. > >> >> >> >> As soon as that information is in DT, support can be added to Linux to > >> >> >> >> make sure the "critical" clocks stay enabled, either through a real driver, > >> >> >> >> or through platform code. > >> >> >> > > >> >> >> > Some do, some don't. For instance, we have one clock which controls > >> >> >> > SPI and I2C that must not be turned off. We discovered this then when > >> >> >> > a suspend was attempted and the board refused to resume. This clock > >> >> >> > also runs one of the critical interconnects that runs from the a9. It > >> >> >> > would be wrong to remove the clk_disable() attempt from the SPI/I2C > >> >> >> > drivers because the same IP on another board might be controlled by a > >> >> >> > different clock which is able to be gated. > >> >> >> > > >> >> >> > There are also clocks which control other interconnects that are not > >> >> >> > connected to any device drivers. If we fail to take references for > >> >> >> > them before clk_disable_unused() is called, again the board hangs. We > >> >> >> > even lose JTAG support. > >> >> >> > >> >> >> Interconnects are buses. Can't you represent those buses in the DT > >> >> >> hierarchy, and give them clocks properties? > >> >> > > >> >> > So instead of this nice succinct, simple, cover all bases > >> >> > (interconnects was just an example, there are bound to be others), > >> >> > generic framework, you are suggesting to write drivers for devices > >> >> > which other than "don't turn my clocks off", Linux can't actually see > >> >> > or control? > >> >> > >> >> DT describes the hardware, not behavior. > >> > > >> > Okay so ... > >> > > >> > /* > >> > * ICNs are not visible/controllable in Linux, but references to their > >> > * clocks must be obtained and retained or the platform will become > >> > * irrecoverably unresponsive. > >> > */ > >> > interconnects@0 { > >> > compatible = "always-on-clk-domain"; > >> > >> st,...flexgen... > >> > >> > clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>, > >> > <&clk_s_c0_flexgen CLK_ICN_LMI>, > >> > <&clk_s_c0_flexgen CLK_ICN_CPU>, > >> > <&clk_s_c0_flexgen CLK_TX_ICN_DMU>; > >> > }; > >> > >> And then you can have platform code that binds against st,...flexgen..., > >> and enables all referenced clocks. > > > > Flexgen isn't a device, it's a clk source. a) writing a device driver > > Sorry, I'm not familiar with ST nomenclature. > So that should become the name of the interconnect/bus. You're still talking about writing function-less drivers for multiple pieces of h/w. We would have a few for ST alone, then multiply that by the number of silicon vendors with similar issues -- which is likely to be most of them. I can understand Rob's "DT has to match h/w" point, but to insist we write lots of empty drivers just to stop some clocks from being gated is barking mad. > > for a clk source seems wrong b) what if on another platform a > > different clock source supplied the clock? Write another driver? And > > what if the ICNs are connected to different clock sources? More > > drivers? c) all of these drivers will only do one thing -- pull a > > reference and keep hold of it. You want 50 drivers (across all > > platforms) doing only that? Or, more sanely, do you want this one > > generic framework driver doing that? > > > >> Alternatively, if you have power domains, you can add a reference to > >> the power domain, and let the power domain driver handle it. > > > > I'm not sure what a power domain driver will do? We need a driver to > > _not_ give up references, that is all. :) > > A power domain driver can do anything it wants. > That includes enabling your interconnect clocks, and keeping them enabled. > > Now, if flexgen is the name of the clock source, then all devices connected > to flexgen are part of the flexgen clock domain, which can be represented > in Linux using the generic PM domain. Do all devices connected to flexgen > need to be handled similarly w.r.t. clocks? If yes, the genpd may be the place > to implement that. Most of the FLEXGEN clocks are fully gateable. It's only a select few which are critical to the running of the system.
diff --git a/Documentation/devicetree/bindings/clock/clk-domain.txt b/Documentation/devicetree/bindings/clock/clk-domain.txt new file mode 100644 index 0000000..b86772f5 --- /dev/null +++ b/Documentation/devicetree/bindings/clock/clk-domain.txt @@ -0,0 +1,35 @@ +Always-on Clock Domain + +Some hardware is contains bunches of clocks which must never be +turned off. If drivers a) fail to obtain a reference to any of +these or b) give up a previously obtained reference during suspend, +the common clk framework will attempt to disable them and the +hardware can fail irrecoverably. Usually, the only way to recover +from these failures is to restart. + +To avoid either of these two scenarios from catastrophically +disabling an otherwise perfectly healthy running system, we have +implemented a clock domain where clocks are consumed and references +are taken, thus preventing them from being shut down by the +framework. + +We use the generic clock bindings found in: + Documentation/devicetree/bindings/clock/clock-bindings.txt + +Required properties: +- compatible : Must be "always-on-clk-domain" + +Example: + +clk-domain { + compatible = "always-on-clk-domain"; + clocks = <&clk_s_c0_flexgen CLK_EXT2F_A9>, + <&clk_s_c0_flexgen CLK_COMPO_DVP>, + <&clk_s_c0_flexgen CLK_MMC_1>, + <&clk_s_c0_flexgen CLK_ICN_SBC>, + <&clk_s_c0_flexgen CLK_ICN_LMI>, + <&clk_s_c0_flexgen CLK_ICN_CPU>, + <&clk_s_c0_flexgen CLK_TX_ICN_DMU>, + <&clk_s_a0_flexgen CLK_IC_LMI0>, + <&clk_m_a9>; +};
Signed-off-by: Lee Jones <lee.jones@linaro.org> --- .../devicetree/bindings/clock/clk-domain.txt | 35 ++++++++++++++++++++++ 1 file changed, 35 insertions(+) create mode 100644 Documentation/devicetree/bindings/clock/clk-domain.txt