[PATCH] drm/amd/mst: clean DP main link status only when unplug mst 1st link

[Wayne Lin]

[Why]
Under DP daisy chain scenario as below:

	Src - Monitor_1 - Monitor_2

If unplug 2nd Monitor_2 and plug in again, observe that Monitor_1
doesn't light up.

When unplug 2nd monitor, we clear the
dc_link->cur_link_settings.lane_count in dm_dp_destroy_mst_connector().
However this link status is a shared data structure by all connected mst
monitors. Although the 2nd monitor is gone, this link status should
still be retained for other connected mst monitors. Otherwise, when we
plug the 2nd monitor in again, we find out that main link is not trained
and do link training again. Payload ID Table for Monitor_1 is ruined and
we don't reallocate it.

[How]
In dm_dp_destroy_mst_connector(), only clean the cur_link_settings when
we no longer do mst mode.

Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 2c10352fa514..526f29598403 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -415,7 +415,10 @@ static void dm_dp_destroy_mst_connector(struct drm_dp_mst_topology_mgr *mgr,
 					   aconnector->dc_sink);
 		dc_sink_release(aconnector->dc_sink);
 		aconnector->dc_sink = NULL;
-		aconnector->dc_link->cur_link_settings.lane_count = 0;
+		mutex_lock(&mgr->lock);
+		if (!mgr->mst_state)
+			aconnector->dc_link->cur_link_settings.lane_count = 0;
+		mutex_unlock(&mgr->lock);
 	}
 
 	drm_connector_unregister(connector);
-- 
2.17.1