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

From: Vinod Polimera
Date: Fri Jan 27 2023 - 10:01:12 EST

> -----Original Message-----
> From: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> Sent: Tuesday, January 24, 2023 10:15 PM
> To: Vinod Polimera <vpolimer@xxxxxxxxxxxxxxxx>
> Cc: Vinod Polimera (QUIC) <quic_vpolimer@xxxxxxxxxxx>; dri-
> devel@xxxxxxxxxxxxxxxxxxxxx; linux-arm-msm@xxxxxxxxxxxxxxx;
> freedreno@xxxxxxxxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; 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
> >
> 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
> > >
> > >
> > > 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?
>
It is not an EDEADLK and return is successful.
Entry and exit times are proper but the work that is getting scheduled after timer expiry is happening very late.

> 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/+/ref
> s/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

--
Thanks
Vinod P.