From: santosh.shilimkar@ti.com (Santosh)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 2/5] cpu_pm: call notifiers during suspend
Date: Fri, 09 Sep 2011 11:57:02 +0530 [thread overview]
Message-ID: <4E69B1B6.2080604@ti.com> (raw)
In-Reply-To: <87ehzqbvvh.fsf@ti.com>
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
next prev parent reply other threads:[~2011-09-09 6:27 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-03 14:39 [PATCH v2 0/5] CPU PM notifiers Santosh Shilimkar
2011-09-03 14:39 ` [PATCH v2 1/5] cpu_pm: Add cpu power management notifiers Santosh Shilimkar
2011-09-09 22:56 ` Andrew Morton
2011-09-10 4:02 ` Santosh
2011-09-10 9:31 ` Santosh
2011-09-12 5:02 ` Santosh
2011-09-13 5:42 ` Santosh
2011-09-03 14:39 ` [PATCH v2 2/5] cpu_pm: call notifiers during suspend Santosh Shilimkar
2011-09-07 20:02 ` Kevin Hilman
2011-09-08 5:16 ` Santosh
2011-09-08 14:01 ` Kevin Hilman
2011-09-08 16:12 ` Santosh
2011-09-08 17:56 ` Kevin Hilman
2011-09-08 18:04 ` Colin Cross
2011-09-08 20:51 ` Kevin Hilman
2011-09-09 6:27 ` Santosh [this message]
2011-09-03 14:39 ` [PATCH v2 3/5] ARM: gic: Use cpu pm notifiers to save gic state Santosh Shilimkar
2011-09-03 14:39 ` [PATCH v2 4/5] ARM: vfp: Use cpu pm notifiers to save vfp state Santosh Shilimkar
2011-09-03 14:39 ` [PATCH v2 5/5] ARM: gic: Allow gic arch extensions to provide irqchip flags Santosh Shilimkar
2011-09-06 2:34 ` [PATCH v2 0/5] CPU PM notifiers Shawn Guo
2011-09-06 5:17 ` Santosh
2011-09-09 18:00 ` Kevin Hilman
2011-09-10 5:53 ` Santosh
2011-09-16 4:50 ` Santosh
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