drm/amd/display: Avoid gpio conflict on MST branch

[Why]
Similar to SST branch, gpio conflict also needs to be avoided on
MST. Without doing so, there is a chance that gpio conflict will
occur if multiple gpio interrupts arrive simultaneously.

[How]
By mutex locking/unlocking &aconnector->hpd_lock,
we won't get gpio conflict when handling hpd.

Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Bhawanpreet Lakha <bhawanpreet.lakha@amd.com>
Acked-by: Zhan Liu <zhan.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2708,8 +2708,7 @@ static void handle_hpd_rx_irq(void *param)
 	 * conflict, after implement i2c helper, this mutex should be
 	 * retired.
 	 */
-	if (dc_link->type != dc_connection_mst_branch)
-		mutex_lock(&aconnector->hpd_lock);
+	mutex_lock(&aconnector->hpd_lock);
 
 	read_hpd_rx_irq_data(dc_link, &hpd_irq_data);
 
@@ -2778,10 +2777,10 @@ static void handle_hpd_rx_irq(void *param)
 	}
 #endif
 
-	if (dc_link->type != dc_connection_mst_branch) {
+	if (dc_link->type != dc_connection_mst_branch)
 		drm_dp_cec_irq(&aconnector->dm_dp_aux.aux);
-		mutex_unlock(&aconnector->hpd_lock);
-	}
+
+	mutex_unlock(&aconnector->hpd_lock);
 }
 
 static void register_hpd_handlers(struct amdgpu_device *adev)