From: "Jerry (Fangzhi) Zuo" <Jerry.Zuo@amd.com>
Date: Fri, 3 Nov 2017 16:04:34 -0400
Subject: drm/amd/display: Check aux channel before MST resume
Git-commit: 30ec2b9717c1c6616332f8ce7c0cb3dd72032a2e
Patch-mainline: v4.15-rc2
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

It is to fix: MST display failed to resume from S3

At the beginning of resume from S3, need to check if mgr->aux is
NULL. Fake MST encoder doesn't have real aux channel.

Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Roman Li <Roman.Li@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -520,7 +520,8 @@ static int detect_mst_link_for_all_conne
 
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
 		aconnector = to_amdgpu_dm_connector(connector);
-		if (aconnector->dc_link->type == dc_connection_mst_branch) {
+		if (aconnector->dc_link->type == dc_connection_mst_branch &&
+		    aconnector->mst_mgr.aux) {
 			DRM_DEBUG_DRIVER("DM_MST: starting TM on aconnector: %p [id: %d]\n",
 					aconnector, aconnector->base.base.id);