diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index e26936309e0754b9e8333a9e3225a7c2b133c0ae..559db96c2f8c24e3db706fa8ce45d38bb7d5d9e9 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -516,6 +516,7 @@ EXPORT_SYMBOL(drm_dp_downstream_max_bpc);
 /**
  * drm_dp_downstream_id() - identify branch device
  * @aux: DisplayPort AUX channel
+ * @id: DisplayPort branch device id
  *
  * Returns branch device id on success or NULL on failure
  */