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

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Date:   Thu, 8 Jul 2021 07:21:52 +0000
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <khsieh@...eaurora.org>,
        dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run
Cc:     abhinavk@...eaurora.org, aravindh@...eaurora.org, airlied@...ux.ie,
        daniel@...ll.ch, bjorn.andersson@...aro.org,
        linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] drm/msm/dp: retrain link when loss of symbol lock detected

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@...eaurora.org>

I guess this is a fix for the original driver, so it should be tagged
with Fixes appropriately.

> ---
>  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);
>