drm/dp_mst: Improve kdocs for drm_dp_check_act_status()

No functional changes.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Sean Paul <sean@poorly.run>
Reviewed-by: Sean Paul <sean@poorly.run>
Link: https://patchwork.freedesktop.org/patch/msgid/20200406221253.1307209-2-lyude@redhat.com

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -4440,10 +4440,14 @@ static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
 
 
 /**
- * drm_dp_check_act_status() - Check ACT handled status.
+ * drm_dp_check_act_status() - Polls for ACT handled status.
  * @mgr: manager to use
  *
- * Check the payload status bits in the DPCD for ACT handled completion.
+ * Tries waiting for the MST hub to finish updating it's payload table by
+ * polling for the ACT handled bit.
+ *
+ * Returns:
+ * 0 if the ACT was handled in time, negative error code on failure.
  */
 int drm_dp_check_act_status(struct drm_dp_mst_topology_mgr *mgr)
 {