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.
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
