linux-kernel - Re: [PATCH v1 3/3] msm: skip the atomic commit of self refresh while PSR running

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Date:   Mon, 3 Apr 2023 19:11:58 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Vinod Polimera <vpolimer@....qualcomm.com>
Cc:     "Vinod Polimera (QUIC)" <quic_vpolimer@...cinc.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "freedreno@...ts.freedesktop.org" <freedreno@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robdclark@...il.com" <robdclark@...il.com>,
        "dianders@...omium.org" <dianders@...omium.org>,
        "swboyd@...omium.org" <swboyd@...omium.org>,
        "Kalyan Thota (QUIC)" <quic_kalyant@...cinc.com>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        "Vishnuvardhan Prodduturi (QUIC)" <quic_vproddut@...cinc.com>,
        "Bjorn Andersson (QUIC)" <quic_bjorande@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
Subject: Re: [PATCH v1 3/3] msm: skip the atomic commit of self refresh while
 PSR running

On Mon, 3 Apr 2023 at 15:01, Vinod Polimera <vpolimer@....qualcomm.com> wrote:
>
> > On Fri, 31 Mar 2023 at 16:59, Vinod Polimera <quic_vpolimer@...cinc.com>
> > wrote:
> > >
> > > In certain CPU stress conditions, there can be a delay in scheduling commit
> > > work and it was observed that PSR commit from a different work queue
> > was
> > > scheduled. Avoid these commits as display is already in PSR mode.
> > >
> > > Signed-off-by: Vinod Polimera <quic_vpolimer@...cinc.com>
> > > ---
> > >  drivers/gpu/drm/msm/msm_atomic.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/msm/msm_atomic.c
> > b/drivers/gpu/drm/msm/msm_atomic.c
> > > index 645fe53..f8141bb 100644
> > > --- a/drivers/gpu/drm/msm/msm_atomic.c
> > > +++ b/drivers/gpu/drm/msm/msm_atomic.c
> > > @@ -192,6 +192,9 @@ int msm_atomic_check(struct drm_device *dev,
> > struct drm_atomic_state *state)
> > >                         new_crtc_state->mode_changed = true;
> > >                         state->allow_modeset = true;
> > >                 }
> > > +
> > > +               if (old_crtc_state->self_refresh_active && new_crtc_state-
> > >self_refresh_active)
> > > +                       return -EINVAL;
> >
> > EINVAL here means that atomic_check will fail if both old and new
> > states are in SR mode. For example, there might be a mode set for
> > another CRTC (while keeping this one in SR mode). I don't think this
> > is correct. We should skip/shortcut the commit, that's true. But I
> > doubt that returning an error here is a proper way to do this. Please
> > correct me if I'm wrong.
>
> If there is a modeset on same crtc with a different connector. The new_crtc_state will not have self_refresh_active set.
> Self_refresh_active is set from the helper library, which will duplicate the old_state and just adds self_refresh_active to true and active to false.
> so we can be confident that if we are checking for self_refresh_active status then it should be coming from the library call.
>
> Also the EINVAL is returned to the self_refresh library API and the function will be retired.

Maybe I misunderstand you here. However, in this way EINVAL is
returned to drm_atomic_check_only() and not to the SR code.

> And self_refresh_active is cleared on every commit : https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/drm_atomic_state_helper.c#n158

And this means that this check will not trigger at all, if I'm not
mistaken. You've added code to msm_atomic_check(), so
drm_self_refresh_helper_alter_state() was not called (yet) and thus
new_crtc_state->self_refresh_active is set to false, fresh after
crtc's duplicate_state.

--
With best wishes
Dmitry