Re: [PATCH Resend v11 05/15] drm/msm/dp: disable self_refresh_aware after entering psr

[Dmitry Baryshkov]

On Tue, 24 Jan 2023 at 17:10, Vinod Polimera <vpolimer@xxxxxxxxxxxxxxxx> wrote:
> > -----Original Message-----
> > From: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > Sent: Tuesday, January 24, 2023 5:52 AM
> > To: Vinod Polimera (QUIC) <quic_vpolimer@xxxxxxxxxxx>; dri-
> > devel@xxxxxxxxxxxxxxxxxxxxx; linux-arm-msm@xxxxxxxxxxxxxxx;
> > freedreno@xxxxxxxxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx
> > Cc: Sankeerth Billakanti (QUIC) <quic_sbillaka@xxxxxxxxxxx>; linux-
> > kernel@xxxxxxxxxxxxxxx; robdclark@xxxxxxxxx; dianders@xxxxxxxxxxxx;
> > swboyd@xxxxxxxxxxxx; Kalyan Thota (QUIC) <quic_kalyant@xxxxxxxxxxx>;
> > Kuogee Hsieh (QUIC) <quic_khsieh@xxxxxxxxxxx>; Vishnuvardhan
> > Prodduturi (QUIC) <quic_vproddut@xxxxxxxxxxx>; Bjorn Andersson (QUIC)
> > <quic_bjorande@xxxxxxxxxxx>; Abhinav Kumar (QUIC)
> > <quic_abhinavk@xxxxxxxxxxx>
> > Subject: Re: [PATCH Resend v11 05/15] drm/msm/dp: disable
> > self_refresh_aware after entering psr
> >
> > WARNING: This email originated from outside of Qualcomm. Please be wary
> > of any links or attachments, and do not enable macros.

I hope such headers can be fixed on your side rather than being sent to the ML.

> >
> > On 19/01/2023 16:26, Vinod Polimera wrote:
> > > From: Sankeerth Billakanti <quic_sbillaka@xxxxxxxxxxx>
> > >
> > > Updated frames get queued if self_refresh_aware is set when the
> > > sink is in psr. To support bridge enable and avoid queuing of update
> > > frames, reset the self_refresh_aware state after entering psr.
> >
> > I'm not convinced by this change. E.g. analogix code doesn't do this.
> > Could you please clarify, why do you need to toggle the
> > self_refresh_aware flag?
> >
> This was done to fix a bug reported by google. The use case is as follows:
>         CPU was running in a low frequency with debug build.
>         When self refresh was triggered by the library, due to system latency, the queued work was not scheduled.
>         There in another commit came and reinitialized the timer for the next PSR trigger.
>         This sequence happened multiple times  and we found there were multiple works which are stuck and yet to be run.

Where were workers stuck? Was it a busy loop around -EDEADLK /
drm_modeset_backoff()? Also, what were ther ewma times for entry/exit
avg times?

I'm asking because the issue that you are describing sounds like a
generic one, not the driver-specific issue. And being generic it
should be handled in a generic fascion, in drm_self_refresh_helper.c.

For example, I can imagine adding a variable to sr_data telling that
the driver is in the process of transitioning to SR. Note: I did not
perform a full research if it is a working solution or not. But from
your description the driver really has to bail out early from
drm_self_refresh_helper_entry_work().

>         As PSR trigger is guarded by self_refresh_aware, we initialized the variable such that, if we are in PSR then until PSR exit, there cannot be any further PSR entry again.
>                 https://chromium.googlesource.com/chromiumos/third_party/kernel/+/refs/tags/v5.15.90/drivers/gpu/drm/drm_self_refresh_helper.c#105

Yes, and that's what triggered my attention. We are using a set of
helpers, that depend on the self_refresh_aware being true. And
suddenly under the hood we disable this flag. I'd say that I can not
predict the effect this will have on the helpers library behaviour.

>         This has solved few flicker issues during the stress testing.
> > >
> > > Signed-off-by: Sankeerth Billakanti <quic_sbillaka@xxxxxxxxxxx>
> > > Signed-off-by: Vinod Polimera <quic_vpolimer@xxxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/msm/dp/dp_drm.c | 27
> > ++++++++++++++++++++++++++-
> > >   1 file changed, 26 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/dp/dp_drm.c
> > b/drivers/gpu/drm/msm/dp/dp_drm.c
> > > index 029e08c..92d1a1b 100644
> > > --- a/drivers/gpu/drm/msm/dp/dp_drm.c
> > > +++ b/drivers/gpu/drm/msm/dp/dp_drm.c
> > > @@ -134,6 +134,8 @@ static void edp_bridge_atomic_enable(struct
> > drm_bridge *drm_bridge,
> > >       struct drm_crtc_state *old_crtc_state;
> > >       struct msm_dp_bridge *dp_bridge = to_dp_bridge(drm_bridge);
> > >       struct msm_dp *dp = dp_bridge->dp_display;
> > > +     struct drm_connector *connector;
> > > +     struct drm_connector_state *conn_state = NULL;
> > >
> > >       /*
> > >        * Check the old state of the crtc to determine if the panel
> > > @@ -150,10 +152,22 @@ static void edp_bridge_atomic_enable(struct
> > drm_bridge *drm_bridge,
> > >
> > >       if (old_crtc_state && old_crtc_state->self_refresh_active) {
> > >               dp_display_set_psr(dp, false);
> > > -             return;
> > > +             goto psr_aware;
> > >       }
> > >
> > >       dp_bridge_atomic_enable(drm_bridge, old_bridge_state);
> > > +
> > > +psr_aware:
> > > +     connector =
> > drm_atomic_get_new_connector_for_encoder(atomic_state,
> > > +                                                     drm_bridge->encoder);
> > > +     if (connector)
> > > +             conn_state =
> > drm_atomic_get_new_connector_state(atomic_state,
> > > +                                                             connector);
> > > +
> > > +     if (conn_state) {
> > > +             conn_state->self_refresh_aware = dp->psr_supported;
> > > +     }
> >
> > No need to wrap a single line statement in brackets.
> >
> > > +
> > >   }
> > >
> > >   static void edp_bridge_atomic_disable(struct drm_bridge *drm_bridge,
> > > @@ -164,6 +178,14 @@ static void edp_bridge_atomic_disable(struct
> > drm_bridge *drm_bridge,
> > >       struct drm_crtc_state *new_crtc_state = NULL, *old_crtc_state = NULL;
> > >       struct msm_dp_bridge *dp_bridge = to_dp_bridge(drm_bridge);
> > >       struct msm_dp *dp = dp_bridge->dp_display;
> > > +     struct drm_connector *connector;
> > > +     struct drm_connector_state *conn_state = NULL;
> > > +
> > > +     connector =
> > drm_atomic_get_old_connector_for_encoder(atomic_state,
> > > +                                                     drm_bridge->encoder);
> > > +     if (connector)
> > > +             conn_state =
> > drm_atomic_get_new_connector_state(atomic_state,
> > > +                                                             connector);
> > >
> > >       crtc = drm_atomic_get_old_crtc_for_encoder(atomic_state,
> > >                                                  drm_bridge->encoder);
> > > @@ -190,6 +212,9 @@ static void edp_bridge_atomic_disable(struct
> > drm_bridge *drm_bridge,
> > >        * when display disable occurs while the sink is in psr state.
> > >        */
> > >       if (new_crtc_state->self_refresh_active) {
> > > +             if (conn_state)
> > > +                     conn_state->self_refresh_aware = false;
> > > +
> > >               dp_display_set_psr(dp, true);
> > >               return;
> > >       } else if (old_crtc_state->self_refresh_active) {
> >
> > --
> > With best wishes
> > Dmitry
>
> Thanks,
> Vinod P.
>


-- 
With best wishes
Dmitry