On Fri, 29 Nov 2024 at 09:59, Xiangxu Yin <quic_xiangxuy@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> ---
> 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
