Re: [PATCH 7/7] drm/msm/dp: retrain link when loss of symbol lock detected

[khsieh]

On 2021-07-08 00:21, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2021-07-06 10:20:20)
> > Main link symbol locked is achieved at end of link training 2. Some
> > dongle main link symbol may become unlocked again if host did not end
> > link training soon enough after completion of link training 2. Host
> > have to re train main link if loss of symbol lock detected before
> > end link training so that the coming video stream can be transmitted
> > to sink properly.
> >
> > Signed-off-by: Kuogee Hsieh <khsieh@xxxxxxxxxxxxxx>
>
> I guess this is a fix for the original driver, so it should be tagged
> with Fixes appropriately.
Actually, this is fix on patch #6 : drm/msm/dp: do not end dp link 
training until video is ready
Should i merge patch #6 and #7 together?
Or can you suggest what should I do?
> > ---
> >  drivers/gpu/drm/msm/dp/dp_ctrl.c | 34 
> > ++++++++++++++++++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c 
> > b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > index 0cb01a9..e616ab2 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > @@ -1661,6 +1661,25 @@ static bool dp_ctrl_any_lane_cr_lose(struct 
> > dp_ctrl_private *ctrl,
> >         return false;
> >  }
> >
> > +static bool dp_ctrl_loss_symbol_lock(struct dp_ctrl_private *ctrl)
> > +{
> > +       u8 link_status[6];
>
> Can we use link_status[DP_LINK_STATUS_SIZE] instead?
>
> > +       u8 status;
> > +       int i;
> > +       int lane = ctrl->link->link_params.num_lanes;
>
> s/lane/num_lanes/
>
> would make the code easier to read
>
> > +
> > +       dp_ctrl_read_link_status(ctrl, link_status);
> > +
> > +       for (i = 0; i < lane; i++) {
> > +               status = link_status[i / 2];
> > +               status >>= ((i % 2) * 4);
> > +               if (!(status & DP_LANE_SYMBOL_LOCKED))
> > +                       return true;
> > +       }
> > +
> > +       return false;
> > +}
> > +
> >  int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
> >  {
> >         int rc = 0;
> > @@ -1777,6 +1796,17 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
> >         return rc;
> >  }
> >
> > +static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
> > +{
> > +       int ret = 0;
>
> Please drop init of ret.
>
> > +       u8 cr_status[2];
> > +       int training_step = DP_TRAINING_NONE;
> > +
> > +       ret = dp_ctrl_setup_main_link(ctrl, cr_status, 
> > &training_step);
>
> as it is assigned here.
>
> > +
> > +       return ret;
>
> And indeed, it could be 'return dp_ctrl_setup_main_link()' instead.
>
> > +}
> > +
> >  int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
> >  {
> >         int ret = 0;
> > @@ -1802,6 +1832,10 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
> >                 }
> >         }
> >
> > +       /* if loss symbol lock happen, then retaining the link */
>
> retain or retrain? The comment seems to be saying what the code says 
> "if
> loss retrain", so the comment is not very useful.
>
> > +       if (dp_ctrl_loss_symbol_lock(ctrl))
> > +               dp_ctrl_link_retrain(ctrl);
> > +
> >         /* stop txing train pattern to end link training */
> >         dp_ctrl_clear_training_pattern(ctrl);