[PATCH v2 2/4] ARM: exynos: Ensure PM domains are powered at initialization

[Ulf Hansson]

On 2 October 2014 11:42, Ulf Hansson <ulf.hansson at linaro.org> wrote:
> On 1 October 2014 21:50, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
>> On Wednesday, October 01, 2014 06:18:58 PM Sylwester Nawrocki wrote:
>>> On 01/10/14 16:41, Ulf Hansson wrote:
>>> > At ->probe() it's common practice for drivers/subsystems to bring their
>>> > devices to full power and without depending on CONFIG_PM_RUNTIME.
>>> >
>>> > We could also expect that drivers/subsystems requires their device's
>>> > corresponding PM domains to be powered, to successfully complete a
>>> > ->probe() sequence.
>>> >
>>> > Align to the behavior above, by ensuring all PM domains are powered
>>> > prior initialization of a generic PM domain.
>>> >
>>> > Do note, since the generic PM domain will try to power off unused PM
>>> > domains at late_init, there should be no increased power consumption
>>> > over time, but potentially during boot.
>>>
>>> Wouldn't it be a better idea to power on the power domains which are
>>> turned off only when CONFIG_PM_RUNTIME is not enabled ? I had a plan
>>> to submit a patch doing that but unfortunately this has fallen through
>>> the cracks. At the moment mach-exynos/pm_domains.c is not even built in
>>> when CONFIG_PM_RUNTIME is disabled.
>
> Yes, that's the approach I also intend to take in the next step.
>
> But, it's not that simple. Since this requires a mechanism for drivers
> to bring their device's PM domains into power state prior doing probe.
> We don't have such today. I do have some ideas about this, but I think
> we need to keep that as a separate discussion.
>
>>>
>>> I don't like the behaviour introduced in this patch to be the default,
>>> i.e. turning all possible power domains during boot sequence, even if
>>> some are not used and not needed. While we're trying to decrease the
>>> power consumption in any possible way this doesn't help at all.
>
> This will hit only during boot, until late_init. Unless you have a
> platform that keeps rebooting all the time, is this really a big
> worry?
>
> Still, I certainly agree that we should strive for a solution where
> it's possible to leave PM domains powered off at init. It's should be

/s/ It's should/ It shouldn't

> too hard to support this from genpd point of view, but
> drivers/subsystems will need some adaptations.
>
>>
>> Agreed (as stated before).
>>
>> And I'm wondering why that comment of mine was ignored?
>
> Sorry, if missed to comment of that. I guess I have at this point.
>
> Kind regards
> Uffe