Re: [PATCH 8/8] drm/arm/malidp: Added the late system pm functions

[Brian Starkey <brian.starkey@arm.com>]

Hi Daniel,

On Fri, Apr 13, 2018 at 05:44:09PM +0200, Daniel Vetter wrote:
>On Mon, Apr 09, 2018 at 05:15:08PM +0100, Brian Starkey wrote:
>> Hi Daniel,
>>
>> On Mon, Apr 09, 2018 at 10:23:37AM +0200, Daniel Vetter wrote:
>> > On Fri, Apr 06, 2018 at 08:02:16PM +0100, Ayan Halder wrote:
>> > > On Tue, Mar 27, 2018 at 01:09:36PM +0200, Daniel Vetter wrote:
>> > > > On Tue, Mar 27, 2018 at 11:59 AM, Ayan Halder <ayan.halder@arm.com> wrote:

[snip]

>>
>> As for why, my understanding is like so:
>>
>> For ->suspend(), we use the DRM helper, which disables the CRTC.
>> Normally disabling the CRTC would be enough to also invoke our
>> pm_runtime callback to do the final clock disable etc., however when a
>> system suspend is in-progress, the core forcibly takes a runtime
>> reference on all devices - preventing any pm_runtime paths from
>> running.
>
>I thought this was fixed. At least I remember we had to add some special
>calls to i915 to opt out of the "do runtime pm as part of suspend/resume"
>behaviour, since it doesn't match what we needed.
>
>See
>
>commit aae4518b3124b29f8dc81c829c704fd2df72e98b
>Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>Date:   Fri May 16 02:46:50 2014 +0200
>
>    PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily
>
>So I thought this stuff was supposed to work now. Adding Rafael Wyzocki,
>he's done plenty presentations recently about exactly this.

AFAIK direct-complete is a different thing - related, but not involved
here.

Ayan's patch is to deal with the case where the device is active
(runtime state = active), when a system suspend is triggered.

The core takes its reference (leaving direct-complete devices
'suspended' if possible, but our device is 'active' and so
direct-complete doesn't apply) and then we start the system suspend
and disable the CRTC.

Normally, after the CRTC is disabled, we rely on PM-core to notice we
can be runtime suspended, but it won't do this during system suspend
because of the reference PM-core took, and so we need to force the
suspend ourselves.

>
>> This means that after the CRTC is disabled in ->suspend(), our normal
>> pm_runtime path will not be invoked, and so the things done in
>> malidp_runtime_pm_suspend() will never happen.
>>
>> We were just following the advice in the kernel-doc to deal with this.
>>
>> The alternative would be to call malidp_runtime_pm_{suspend,resume}
>> from the "not late" hooks, but I'd ask why?
>>
>> > Also, you still haven't explained what exactly the dependency is.
>>
>> Because there isn't one :-)
>
>Hm, if there really isn't one, then I guess it's ok. But it's way too easy
>to screw this up, have an accidental depency on a different device. And
>then you try to fix this up. Having a suspend_late hook still smells fishy
>to me, but I might be out of the loop.
>-Daniel
>

Hopefully Rafael can set us straight. The kerneldoc doesn't make
suspend_late sound exceptional, but kernel-doc isn't perfect :-)

Thanks for the review,
-Brian

>
>
>>
>> Thanks,
>> -Brian
>>
>> > -Daniel
>> >
>> > >
>> > > > >> > ---
>> > > > >> >  drivers/gpu/drm/arm/malidp_drv.c | 17 +++++++++++++++++
>> > > > >> >  1 file changed, 17 insertions(+)
>> > > > >> >
>> > > > >> > diff --git a/drivers/gpu/drm/arm/malidp_drv.c b/drivers/gpu/drm/arm/malidp_drv.c
>> > > > >> > index bd44a6d..f6124d8 100644
>> > > > >> > --- a/drivers/gpu/drm/arm/malidp_drv.c
>> > > > >> > +++ b/drivers/gpu/drm/arm/malidp_drv.c
>> > > > >> > @@ -766,8 +766,25 @@ static int __maybe_unused malidp_pm_resume(struct device *dev)
>> > > > >> >     return 0;
>> > > > >> >  }
>> > > > >> >
>> > > > >> > +static int __maybe_unused malidp_pm_suspend_late(struct device *dev)
>> > > > >> > +{
>> > > > >> > +   if (!pm_runtime_status_suspended(dev)) {
>> > > > >> > +           malidp_runtime_pm_suspend(dev);
>> > > > >> > +           pm_runtime_set_suspended(dev);
>> > > > >> > +   }
>> > > > >> > +   return 0;
>> > > > >> > +}
>> > > > >> > +
>> > > > >> > +static int __maybe_unused malidp_pm_resume_early(struct device *dev)
>> > > > >> > +{
>> > > > >> > +   malidp_runtime_pm_resume(dev);
>> > > > >> > +   pm_runtime_set_active(dev);
>> > > > >> > +   return 0;
>> > > > >> > +}
>> > > > >> > +
>> > > > >> >  static const struct dev_pm_ops malidp_pm_ops = {
>> > > > >> >     SET_SYSTEM_SLEEP_PM_OPS(malidp_pm_suspend, malidp_pm_resume) \
>> > > > >> > +   SET_LATE_SYSTEM_SLEEP_PM_OPS(malidp_pm_suspend_late, malidp_pm_resume_early) \
>> > > > >> >     SET_RUNTIME_PM_OPS(malidp_runtime_pm_suspend, malidp_runtime_pm_resume, NULL)
>> > > > >> >  };
>> > > > >> >
>> > > > >> > --
>> > > > >> > 2.7.4
>> > > > >> >
>> > > > >> > _______________________________________________
>> > > > >> > dri-devel mailing list
>> > > > >> > dri-devel@lists.freedesktop.org
>> > > > >> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>> > > > >>
>> > > > >> --
>> > > > >> Daniel Vetter
>> > > > >> Software Engineer, Intel Corporation
>> > > > >> http://blog.ffwll.ch
>> > > > >> _______________________________________________
>> > > > >> dri-devel mailing list
>> > > > >> dri-devel@lists.freedesktop.org
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>> > > > > _______________________________________________
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>> > > >
>> > > >
>> > > >
>> > > > --
>> > > > Daniel Vetter
>> > > > Software Engineer, Intel Corporation
>> > > > +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>> >
>> > --
>> > Daniel Vetter
>> > Software Engineer, Intel Corporation
>> > http://blog.ffwll.ch
>
>-- 
>Daniel Vetter
>Software Engineer, Intel Corporation
>http://blog.ffwll.ch