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

[gareth . yu]

From: Gareth Yu <gareth...@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.upadh...@intel.com>
Cc : Matt Roper <matthew.d.ro...@intel.com>
Cc : Ville Syrjälä <ville.syrj...@linux.intel.com>
Signed-off-by: Gareth Yu <gareth...@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