From: "Jerry (Fangzhi) Zuo" <Jerry.Zuo@amd.com>
Date: Tue, 12 Dec 2017 17:33:57 -0500
Subject: drm/amd/display: Fix topology change issue in MST rehook
Git-commit: 1c7571fb29c33f90639d477d24514609cd738cd9
Patch-mainline: v4.16-rc5
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

When topology changed and rehook up MST display to the same DP
connector, need to take care of drm_dp_mst_port object.

Due to the topology is changed, drm_dp_mst_port and corresponding
i2c_algorithm object could be NULL in such situation.

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_mst_types.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- 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
@@ -189,6 +189,12 @@ void dm_dp_mst_dc_sink_create(struct drm
 			.link = aconnector->dc_link,
 			.sink_signal = SIGNAL_TYPE_DISPLAY_PORT_MST };
 
+	/*
+	 * TODO: Need to further figure out why ddc.algo is NULL while MST port exists
+	 */
+	if (!aconnector->port || !aconnector->port->aux.ddc.algo)
+		return;
+
 	edid = drm_dp_mst_get_edid(connector, &aconnector->mst_port->mst_mgr, aconnector->port);
 
 	if (!edid) {