Re: [PATCH 8/8] drm/arm/malidp: Added the late system pm functions
From: Brian Starkey
Date: Fri Apr 13 2018 - 12:03:00 EST
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@xxxxxxx> 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@xxxxxxxxx>
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
> > > >> >
> > > >> > _______________________________________________
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> > > >>
> > > >> --
> > > >> Daniel Vetter
> > > >> Software Engineer, Intel Corporation
> > > >> http://blog.ffwll.ch
> > > >> _______________________________________________
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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