linux-kernel - Re: [PATCH v4 2/3] PM / sleep: Go direct

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Message-ID: <CAAObsKDDEi8CQQp2apARBT9pnWiGghOS-ry_sbw7-GgBhydw2g@mail.gmail.com>
Date:	Thu, 16 Jul 2015 10:47:51 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v4 2/3] PM / sleep: Go direct_complete if driver has no callbacks

On 16 July 2015 at 02:41, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Wednesday, July 15, 2015 02:47:50 PM Alan Stern wrote:
>> On Wed, 15 Jul 2015, Tomeu Vizoso wrote:
>>
>> > If a suitable prepare callback cannot be found for a given device and
>> > its driver has no PM callbacks at all, assume that it can go direct to
>> > complete when the system goes to sleep.
>> >
>> > The reason for this is that there's lots of devices in a system that do
>> > no PM at all and there's no reason for them to prevent their ancestors
>> > to do direct_complete if they can support it.
>> >
>> > Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
>> > ---
>> >
>> >  drivers/base/power/main.c | 17 +++++++++++++++++
>> >  1 file changed, 17 insertions(+)
>> >
>> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
>> > index 1710c26ba097..edda3f233c7c 100644
>> > --- a/drivers/base/power/main.c
>> > +++ b/drivers/base/power/main.c
>> > @@ -1540,6 +1540,21 @@ int dpm_suspend(pm_message_t state)
>> >     return error;
>> >  }
>> >
>> > +static bool driver_has_no_pm_callbacks(struct device_driver *drv)
>> > +{
>> > +   if (!drv->pm)
>> > +           return true;
>> > +
>> > +   return !drv->pm->prepare &&
>> > +          !drv->pm->suspend &&
>> > +          !drv->pm->suspend_late &&
>> > +          !drv->pm->suspend_noirq &&
>> > +          !drv->pm->resume_noirq &&
>> > +          !drv->pm->resume_early &&
>> > +          !drv->pm->resume &&
>> > +          !drv->pm->complete;
>> > +}
>>
>> This isn't exactly what I meant.  We also need to check the dev_pm_ops
>> fields in dev->pm_domain, dev->type, dev->class, and dev->bus.  Only if
>> _all_ of these callbacks are missing should we use direct_complete.
>
> Also checking that on every suspend is kind of wasteful, because those things
> do not change very often.

Do you have any suggestion on when would be a good time to do that
check? device_pm_sleep_init() and device_pm_add() are unfortunately
too early.

Alternatively we could check once on the first suspend and cache it,
but I'm not sure that complexity would be worth it.

Thanks,

Tomeu

> Thanks,
> Rafael
>
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