[PATCH v2 2/5] cpu_pm: call notifiers during suspend

[Kevin Hilman]

Santosh <santosh.shilimkar at ti.com> writes:

> On Thursday 08 September 2011 07:31 PM, Kevin Hilman 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>
>>>>>
>>>>> Implements syscore_ops in cpu_pm to call the cpu and
>>>>> cpu cluster notifiers during suspend and resume,
>>>>> allowing drivers receiving the notifications to
>>>>> avoid implementing syscore_ops.
>>>>>
>>>>> Signed-off-by: Colin Cross<ccross at android.com>
>>>>> [santosh.shilimkar at ti.com: Rebased against 3.1-rc4]
>>>>> Signed-off-by: Santosh Shilimkar<santosh.shilimkar at ti.com>
>>>>
>>>> I don't think using syscore_ops is right here.  The platform code should
>>>> decide where in its own suspend path the notifiers should be triggered.
>>>>
>>>> The reason is because while the syscore_ops run late in the suspend
>>>> path, they still run before some platform-specific decisions about the
>>>> low-power states are made.  That means that any notifiers that need to
>>>> use information about the target low-power state (e.g. whether context
>>>> will be lost or not) cannot do so since that information has not yet
>>>> been decided until the platform_suspend_ops->enter() runs.
>>>>
>>> Initially I thought the same but in general S2R, platform doesn't
>>> support multiple states like CPUIDLE. On OMAP, we do have a debug
>>> option to choose the state but on real product, it's always the
>>> deepest supported state is used. So the driver saving the
>>> full context for S2R, should be fine.
>>>
>>> Ofcourse for CPUIDLE, the notifier call chain decisions are left
>>> with platform CPUIDLE drivers since there can be multiple low
>>> power states and the context save/restore has to be done based
>>> on low power states.
>>>
>>> The advantage with this is, the platform code is clean from the
>>> notfiers calls. CPUIDLE driver needs to call the different notifier
>>> events based on C-states and that perfectly works.
>>>
>>> I liked this simplification for the S2R. Down side is in S2R if you
>>> don't plan to hit deepest state, drivers end up saving full context
>>> which is fine I guess.
>>
>> That's not the downside I'm worried about.
>>
>> If you have a driver that has a notifier, presumably it has something it
>> wants to do to prepare for suspend *and* for idle, and you'd only want a
>> single notifier callback in the driver to be used for both.  That
>> callback would look something like:
>>
>>     start_preparing_for_suspend();
>>
>>     if (next_state == OFF)
>>        save_context();
>>
>>     finish_preparing_for_suspend();
>>
>>
>> The problem with the current cpu_*_pm_enter() calls in syscore_ops is
>> that they happen before the next states are programmed, so during
>> suspend the 'if (next_state == off)' above would never be true, but
>> during idle it might be.
>>
> Point taken and now I agree with you.
>
> I am going to drop this patch unless and until somebody shouts at me.
> What that means is platform code need to take care of suspend case
> as well which is trivial change.

Agreed.

Thanks,

Kevin