[PATCH 7/8] drm/msm/dp: Retry Link Training 2 with lower pattern

[Dmitry Baryshkov]

On Fri, 29 Nov 2024 at 09:59, Xiangxu Yin <quic_xiangxuy at quicinc.com> wrote:
>
> Add a mechanism to retry Link Training 2 by lowering the pattern level
> when the link training #2 first attempt fails. This approach enhances
> compatibility, particularly addressing issues caused by certain hub
> configurations.

Please reference corresponding part of the standard, describing this lowering.

>
> Signed-off-by: Xiangxu Yin <quic_xiangxuy at quicinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 34 ++++++++++++++++++++++++++++++----
>  1 file changed, 30 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 49c8ce9b2d0e57a613e50865be3fe98e814d425a..b1862294cb98c9f756b0108b7670cb42de37bae4 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1220,7 +1220,7 @@ static void msm_dp_ctrl_clear_training_pattern(struct msm_dp_ctrl_private *ctrl)
>  }
>
>  static int msm_dp_ctrl_link_train_2(struct msm_dp_ctrl_private *ctrl,
> -                       int *training_step)
> +                       int *training_step, bool downgrade)
>  {
>         int tries = 0, ret = 0;
>         u8 pattern;
> @@ -1243,6 +1243,28 @@ static int msm_dp_ctrl_link_train_2(struct msm_dp_ctrl_private *ctrl,
>                 state_ctrl_bit = 2;
>         }
>
> +       /*
> +        * DP link training uses the highest allowed pattern by default.
> +        * If it fails, the pattern is downgraded to improve cable and monitor compatibility.
> +        */
> +       if (downgrade) {
> +               switch (pattern) {
> +               case DP_TRAINING_PATTERN_4:
> +                       pattern = DP_TRAINING_PATTERN_3;
> +                       state_ctrl_bit = 3;
> +                       break;
> +               case DP_TRAINING_PATTERN_3:
> +                       pattern = DP_TRAINING_PATTERN_2;
> +                       state_ctrl_bit = 2;
> +                       break;
> +               default:
> +                       break;
> +               }
> +       }
> +
> +       drm_dbg_dp(ctrl->drm_dev, "pattern(%d) state_ctrl_bit(%d) downgrade(%d)\n",
> +               pattern, state_ctrl_bit, downgrade);
> +
>         ret = msm_dp_catalog_ctrl_set_pattern_state_bit(ctrl->catalog, state_ctrl_bit);
>         if (ret)
>                 return ret;
> @@ -1311,10 +1333,14 @@ static int msm_dp_ctrl_link_train(struct msm_dp_ctrl_private *ctrl,
>         /* print success info as this is a result of user initiated action */
>         drm_dbg_dp(ctrl->drm_dev, "link training #1 successful\n");
>
> -       ret = msm_dp_ctrl_link_train_2(ctrl, training_step);
> +       ret = msm_dp_ctrl_link_train_2(ctrl, training_step, false);
>         if (ret) {
> -               DRM_ERROR("link training #2 failed. ret=%d\n", ret);
> -               goto end;
> +               drm_dbg_dp(ctrl->drm_dev, "link training #2 failed, retry downgrade.\n");
> +               ret = msm_dp_ctrl_link_train_2(ctrl, training_step, true);
> +               if (ret) {
> +                       DRM_ERROR("link training #2 failed. ret=%d\n", ret);
> +                       goto end;
> +               }
>         }
>
>         /* print success info as this is a result of user initiated action */
>
> --
> 2.25.1
>


-- 
With best wishes
Dmitry