[PATCH v2 2/5] cpu_pm: call notifiers during suspend
santosh.shilimkar at ti.com
Fri Sep 9 02:27:02 EDT 2011
On Friday 09 September 2011 02:21 AM, Kevin Hilman wrote:
> Colin Cross<ccross at android.com> writes:
>> On Thu, Sep 8, 2011 at 7:01 AM, Kevin Hilman<khilman at ti.com> wrote:
>>> Santosh<santosh.shilimkar at ti.com> writes:
>>>> On Thursday 08 September 2011 01:32 AM, Kevin Hilman wrote:
>>>>> Santosh Shilimkar<santosh.shilimkar at ti.com> writes:
>>>>>> From: Colin Cross<ccross at android.com>
>> These notifiers are designed for drivers that are tightly coupled to
>> the cpu, and shared across multiple architectures (mostly GIC and
> 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
> 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
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