drm/amd/dc: Fix a missing check bug in dm_dp_mst_detect()

stable inclusion
from stable-5.10.50
commit 5885fce7b43919406b32d1c942c9b496aac3abbc
bugzilla: 174522 https://gitee.com/openeuler/kernel/issues/I4DNFY

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5885fce7b43919406b32d1c942c9b496aac3abbc

--------------------------------

[ Upstream commit 655c0ed1 ]

In dm_dp_mst_detect(), We should check whether or not @connector
has been unregistered from userspace. If the connector is unregistered,
we should return disconnected status.

Fixes: 4562236b ("drm/amd/dc: Add dc display driver (v2)")
Signed-off-by: NYingjie Wang <wangyingjie55@126.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c

@@ -268,6 +268,9 @@ dm_dp_mst_detect(struct drm_connector *connector,
 	struct amdgpu_dm_connector *aconnector = to_amdgpu_dm_connector(connector);
 	struct amdgpu_dm_connector *master = aconnector->mst_port;
 
+	if (drm_connector_is_unregistered(connector))
+		return connector_status_disconnected;
+
 	return drm_dp_mst_detect_port(connector, ctx, &master->mst_mgr,
 				      aconnector->port);
 }