Re: [PATCH] drm/msm/dp: force link training for display resolution change

[Kuogee Hsieh]

On 5/26/2022 5:07 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-05-26 10:26:18)
> > During display resolution changes display have to be disabled first
> > followed by display enable with new resolution. This patch force
> > main link always be retrained during display enable procedure to
> > simplify implementation instead of manually kicking of irq_hpd
> > handle.
> How is that better? Can you please describe how it improves things? I
> suppose it avoids some round trips through the event queue just to turn
> on the display?

This try to fix customer issues which only happen on one particular 
panel which fails on display resolution changes sometimes.

I will add more description.

> > Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
> Any Fixes tag? Or it's not fixing anything, just making things simpler?
will add.
> > diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > index 5ddb4e8..8b71013 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.h b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> > index 2433edb..dcc7af21 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
> > +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> > @@ -20,7 +20,7 @@ struct dp_ctrl {
> >   };
> >
> >   int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl);
> > -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl);
> > +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train);
> Can we have another API like dp_ctrl_on_stream_retrain()? Or name
> 'force_link_train' to 'retrain'?
>
> >   int dp_ctrl_off_link_stream(struct dp_ctrl *dp_ctrl);
> >   int dp_ctrl_off(struct dp_ctrl *dp_ctrl);
> >   void dp_ctrl_push_idle(struct dp_ctrl *dp_ctrl);
> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > index bfc6581..9246421 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > @@ -892,7 +892,7 @@ static int dp_display_enable(struct dp_display_private *dp, u32 data)
> Any reason why dp_display_enable() is forward declared and why it takes
> a u32 data argument? It's not part of the eventqueue calling code from
> what I can tell so we should be able to rename 'data' to 'retrain_link'?
>
> >                  return 0;
> >          }
> >
> > -       rc = dp_ctrl_on_stream(dp->ctrl);
> > +       rc = dp_ctrl_on_stream(dp->ctrl, data);
> >          if (!rc)
> >                  dp_display->power_on = true;
> >
> > @@ -1594,6 +1594,7 @@ int msm_dp_display_enable(struct msm_dp *dp, struct drm_encoder *encoder)
> >          int rc = 0;
> >          struct dp_display_private *dp_display;
> >          u32 state;
> > +       bool force_link_train = false;
> >
> >          dp_display = container_of(dp, struct dp_display_private, dp_display);
> >          if (!dp_display->dp_mode.drm_mode.clock) {
> > @@ -1622,10 +1623,12 @@ int msm_dp_display_enable(struct msm_dp *dp, struct drm_encoder *encoder)
> >
> >          state =  dp_display->hpd_state;
> >
> > -       if (state == ST_DISPLAY_OFF)
> > +       if (state == ST_DISPLAY_OFF) {
> >                  dp_display_host_phy_init(dp_display);
> > +               force_link_train = 1;
> Use true instead of 1 if the type is a bool please.
>
> > +       }
> >
> > -       dp_display_enable(dp_display, 0);
> > +       dp_display_enable(dp_display, force_link_train);
> >
> >          rc = dp_display_post_enable(dp);
> >          if (rc) {