Messages in this thread | | | Date | Fri, 09 Sep 2011 11:57:02 +0530 | From | Santosh <> | Subject | Re: [PATCH v2 2/5] cpu_pm: call notifiers during suspend |
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On Friday 09 September 2011 02:21 AM, Kevin Hilman wrote: > Colin Cross<ccross@android.com> writes: > >> On Thu, Sep 8, 2011 at 7:01 AM, Kevin Hilman<khilman@ti.com> wrote: >>> Santosh<santosh.shilimkar@ti.com> writes: >>> >>>> On Thursday 08 September 2011 01:32 AM, Kevin Hilman wrote: >>>>> Santosh Shilimkar<santosh.shilimkar@ti.com> writes: >>>>> >>>>>> From: Colin Cross<ccross@android.com> [...]
>> >> These notifiers are designed for drivers that are tightly coupled to >> the cpu, and shared across multiple architectures (mostly GIC and >> VFP). > > That is certainly the initial intended usage, and I understand that > design, but they are useful for much more. > > Specifically, consider devices whose power transitions need to be > tightly coupled with the CPU, but are in different power domains. > Notifiers for these devices may need to be coordinated with > platform-specific events. > > Also, it's not only about context save for off-mode. Some of these > tightly-coupled devices have other work to do besides context > save/restore, and CPU PM notifiers are useful there. A dumb example off > the top of my head: pins (e.g. GPIOs), that need to be mux'd into safe > mode to avoid glitches when coming back from off. (admittedly, this is > broken HW, but we all know broken HW is part of life.) > >> In practice, all of these devices are off in every suspend >> state, because nobody leaves the CPU on in suspend. > > Sure, but you might leave other power domains on (or in retention) > during suspend, and these domains might contain some of the devices > whose power transitions are coupled with CPU transitions and thus using > CPU PM notifiers. > > Also, so far we've only talked about suspend, but the CPU (and other > power domains) might also go off during idle. The approach in $SUBJECT > patch addresses suspend but not idle, which means it's up to > platform-specific code to trigger the notifiers for idle. I think it > should be the same for suspend. > >> The (next_state == OFF) api you refer to would have to be something >> architecture specific, since the power state handling is very >> different on every platform, so it's not something that would ever be >> included in drivers that I imagined would be using these notifiers. > > Sure, but you created something so useful that it can be used in other > areas than you initially imagined. :) Thanks! > > I wouldn't imagine arch-specific being used in those generic drivers > either, but in addition to the drivers you imagined, I'm already trying > to the notifiers in drivers that are platform-specific. I only imagine > using the "next state" type of checking in platform-specific code, not > in generic ones. > > Note however that I'm certainly not arguing that the notifiers should > not be called in suspend. I'm only arguing that it should be up to > platform-specific code when to call them because of possible > platform-specific pre-requisites in platform-specific notifier > callbacks. > > IMO, there are 2 options. > > 1) leave it up to platform-specific code when to trigger the notifiers > for *both* suspend and idle PM transitions > > 2) trigger the notifiers in arch-independent code for both suspend and > idle *but* provide a way that platform-specific code can disable > them in favor of using platform-specific trigger points. > > If most platforms really don't care, then maybe (2) would be the > better approach. That's fine with me as long as there's a way to > disable them so platform-specific ones can be used. > I think, we should keep the notifiers simple and option 1 the one thing we should consider. It's just easy to take care of IDLE and suspend together.
Regards Santosh
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