diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 86e1a61b6b6d..70be5719e403 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -178,13 +178,13 @@ static int
 drm_dp_mst_rad_to_str(const u8 rad[8], u8 lct, char *out, size_t len)
 {
 	int i;
-	u8 unpacked_rad[16];
+	u8 unpacked_rad[16] = {};
 
-	for (i = 0; i < lct; i++) {
+	for (i = 1; i < lct; i++) {
 		if (i % 2)
-			unpacked_rad[i] = rad[i / 2] >> 4;
+			unpacked_rad[i] = rad[(i - 1) / 2] >> 4;
 		else
-			unpacked_rad[i] = rad[i / 2] & BIT_MASK(4);
+			unpacked_rad[i] = rad[(i - 1) / 2] & 0xF;
 	}
 
 	/* TODO: Eventually add something to printk so we can format the rad
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index ddb9231d0309..9911264e0b15 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -232,6 +232,13 @@ struct drm_dp_mst_branch {
 	 */
 	struct list_head destroy_next;
 
+	/**
+	 * @rad: Relative Address of the MST branch.
+	 * For &drm_dp_mst_topology_mgr.mst_primary, it's rad[8] are all 0,
+	 * unset and unused. For MST branches connected after mst_primary,
+	 * in each element of rad[] the nibbles are ordered by the most
+	 * signifcant 4 bits first and the least significant 4 bits second.
+	 */
 	u8 rad[8];
 	u8 lct;
 	int num_ports;