[PATCH] drm/amd/display: Defer handling mst up request in resume

[Wayne Lin <wayne.lin@xxxxxxx>]

[Why]
Like commit ec5fa9fcdeca ("drm/amd/display: Adjust the MST resume flow"), we
want to avoid handling mst topology changes before restoring the old state.
If we enable DP_UP_REQ_EN before calling drm_atomic_helper_resume(), have
changce to handle CSN event first and fire hotplug event before restoring the
cached state.

[How]
Disable mst branch sending up request event before we restoring the cached state.
DP_UP_REQ_EN will be set later when we call drm_dp_mst_topology_mgr_resume().

Cc: Mario Limonciello <mario.limonciello@xxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Hersen Wu <hersenxs.wu@xxxxxxx>
Signed-off-by: Wayne Lin <wayne.lin@xxxxxxx>
Tested-by: Daniel Wheeler <daniel.wheeler@xxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index c863f400024b..ecf5752ef35f 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -2429,7 +2429,6 @@ static void resume_mst_branch_status(struct drm_dp_mst_topology_mgr *mgr)
 
 	ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
 				 DP_MST_EN |
-				 DP_UP_REQ_EN |
 				 DP_UPSTREAM_IS_SRC);
 	if (ret < 0) {
 		drm_dbg_kms(mgr->dev, "mst write failed - undocked during suspend?\n");