Patch "drm/dp/mst: Restore primary hub guid on resume" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

drm/dp/mst: Restore primary hub guid on resume

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-dp-mst-restore-primary-hub-guid-on-resume.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lyude <[email protected]>
Date: Wed, 13 Apr 2016 16:50:18 -0400
Subject: drm/dp/mst: Restore primary hub guid on resume

From: Lyude <[email protected]>

commit 9dc0487d96a0396367a1451b31873482080b527f upstream.

Some hubs are forgetful, and end up forgetting whatever GUID we set previously after we do a suspend/resume cycle. This can lead to hotplugging breaking (along with probably other things) since the hub will start sending connection notifications with the wrong GUID. As such, we need to check on resume whether or not the GUID the hub is giving us is valid.

---
 drivers/gpu/drm/drm_dp_mst_topology.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

@@ -2116,6 +2116,8 @@ int drm_dp_mst_topology_mgr_resume(struc
 
 	if (mgr->mst_primary) {
 		int sret;
+		u8 guid[16];
+
 		sret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, mgr->dpcd, DP_RECEIVER_CAP_SIZE);
 		if (sret != DP_RECEIVER_CAP_SIZE) {
 			DRM_DEBUG_KMS("dpcd read failed - undocked during suspend?\n");

@@ -2130,6 +2132,16 @@ int drm_dp_mst_topology_mgr_resume(struc
 			ret = -1;
 			goto out_unlock;
 		}
+
+		/* Some hubs forget their guids after they resume */
+		sret = drm_dp_dpcd_read(mgr->aux, DP_GUID, guid, 16);
+		if (sret != 16) {
+			DRM_DEBUG_KMS("dpcd read failed - undocked during suspend?\n");
+			ret = -1;
+			goto out_unlock;
+		}
+		drm_dp_check_mstb_guid(mgr->mst_primary, guid);
+
 		ret = 0;
 	} else
 		ret = -1;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/drm-dp-mst-restore-primary-hub-guid-on-resume.patch queue-4.4/drm-dp-mst-validate-port-in-drm_dp_payload_send_msg.patch queue-4.4/drm-i915-fix-race-condition-in-intel_dp_destroy_mst_connector.patch queue-4.4/drm-dp-mst-get-validated-port-ref-in-drm_dp_update_payload_part1.patch