drm/mst: Fix error handling during MST sideband message reception

From Imre Deak
3383334a6cf38af6843793e343c95081b02773f1 in linux-4.4.y/4.4.79
448421b5e93b9177c5698f0cf6f5e72d2995eeca in mainline linux

ok kettenis@

1 files changed, 8 insertions, 2 deletions

diff --git a/sys/dev/pci/drm/drm_dp_mst_topology.c b/sys/dev/pci/drm/drm_dp_mst_topology.c
index 361964eb13d..07e7cbbd622 100644
--- a/sys/dev/pci/drm/drm_dp_mst_topology.c
+++ b/sys/dev/pci/drm/drm_dp_mst_topology.c
@@ -2199,11 +2199,17 @@ static void drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up)
 		ret = drm_dp_dpcd_read(mgr->aux, basereg + curreply,
 				    replyblock, len);
 		if (ret != len) {
-			DRM_DEBUG_KMS("failed to read a chunk\n");
+			DRM_DEBUG_KMS("failed to read a chunk (len %d, ret %d)\n",
+				      len, ret);
+			return;
 		}
+
 		ret = drm_dp_sideband_msg_build(msg, replyblock, len, false);
-		if (ret == false)
+		if (!ret) {
 			DRM_DEBUG_KMS("failed to build sideband msg\n");
+			return;
+		}
+
 		curreply += len;
 		replylen -= len;
 	}