linux-kernel - Re: [PATCH] drm/msm/dpu: ensure device suspend happens during PM sleep

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Message-ID: <CAD=FV=VxeCUEEFi9T0Jand3EWkaQTLnQkT3v5yjyjLi4yDeQ-w@mail.gmail.com>
Date:   Wed, 25 Mar 2020 08:50:05 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     Kalyan Thota <kalyan_t@...eaurora.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Sean Paul <seanpaul@...omium.org>,
        "Kristian H. Kristensen" <hoegsberg@...omium.org>,
        Jeykumar Sankaran <jsanka@...eaurora.org>,
        mkrishn@...eaurora.org, travitej@...eaurora.org,
        nganji@...eaurora.org
Subject: Re: [PATCH] drm/msm/dpu: ensure device suspend happens during PM sleep

Hi,

On Wed, Mar 25, 2020 at 8:40 AM Rob Clark <robdclark@...il.com> wrote:
>
> On Tue, Mar 24, 2020 at 7:35 AM Doug Anderson <dianders@...omium.org> wrote:
> >
> > Hi,
> >
> > On Sun, Mar 22, 2020 at 11:14 PM Kalyan Thota <kalyan_t@...eaurora.org> wrote:
> > >
> > > "The PM core always increments the runtime usage counter
> > > before calling the ->suspend() callback and decrements it
> > > after calling the ->resume() callback"
> > >
> > > DPU and DSI are managed as runtime devices. When
> > > suspend is triggered, PM core adds a refcount on all the
> > > devices and calls device suspend, since usage count is
> > > already incremented, runtime suspend was not getting called
> > > and it kept the clocks on which resulted in target not
> > > entering into XO shutdown.
> > >
> > > Add changes to manage runtime devices during pm sleep.
> > >
> > > Changes in v1:
> > >  - Remove unnecessary checks in the function
> > >      _dpu_kms_disable_dpu (Rob Clark).
> >
> > I'm wondering what happened with my feedback on v1, AKA:
> >
> > https://lore.kernel.org/r/CAD=FV=VxzEV40g+ieuEN+7o=34+wM8MHO8o7T5zA1Yosx7SVWg@mail.gmail.com
> >
> > Maybe you didn't see it?  ...or if you or Rob think I'm way off base
> > (always possible) then please tell me so.
> >
>
> At least w/ the current patch, disable_dpu should not be called for
> screen-off (although I'd hope if all the screens are off the device
> would suspend).

OK, that's good.

> But I won't claim to be a pm expert.. so not really
> sure if this is the best approach or not.  I don't think our
> arrangement of sub-devices under a parent is completely abnormal, so
> it does feel like there should be a simpler solution..

I think the other arguments about asymmetry are still valid and I've
fixed bugs around this type of thing in the past.  For instance, see
commit f7ccbed656f7 ("drm/rockchip: Suspend DP late").


-Doug