[PATCH] drm/i915/display: Fixed the main link lost in MST

[gareth.yu at intel.com]

From: Gareth Yu <gareth.yu at intel.com>

Re-train the main link when the sink asserts a HPD for the main lnk
lost.

v4:  detect the main link state by intel_dp_needs_link_retrain
     instead of intel_dp_mst_link_status because the main link
     state can't detect correctly sometimes by
     intel_dp_mst_link_status

Cc : Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay at intel.com>
Cc : Matt Roper <matthew.d.roper at intel.com>
Cc : Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Gareth Yu <gareth.yu at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index e05e25cd4a94..e1b60303b256 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -5849,8 +5849,14 @@ intel_dp_detect(struct drm_connector *connector,
 	/* Can't disconnect eDP */
 	if (intel_dp_is_edp(intel_dp))
 		status = edp_detect(intel_dp);
-	else if (intel_digital_port_connected(encoder))
+	else if (intel_digital_port_connected(encoder)) {
 		status = intel_dp_detect_dpcd(intel_dp);
+		if (status == connector_status_connected && intel_dp->is_mst &&
+		    intel_dp_needs_link_retrain(intel_dp)) {
+			if (intel_dp_retrain_link(encoder, ctx))
+				status = connector_status_disconnected;
+		}
+	}
 	else
 		status = connector_status_disconnected;
 
-- 
2.25.1