FAILED: patch "[PATCH] drm/i915: Perform link quality check unconditionally during" failed to apply to 4.11-stable tree

The patch below does not apply to the 4.11-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <[email protected]>
Date: Wed, 12 Apr 2017 22:30:17 +0300
Subject: [PATCH] drm/i915: Perform link quality check unconditionally during
long pulse
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Apparently some DP sinks are a little nuts and cause HPD to drop intermittently during modesets. This happens eg. on an ASUS PB287Q. In oder to recover from this we can't really use the previous connector status to determine if the link needs retraining, so let's just ignore that piece of information and do the retrain unconditionally. We do of course still check whether the link is supposed to be running or not.

To actually get read out the EDID and update things properly we also need to nuke the goto out added by commit 7d23e3c37bb3 ("drm/i915: Cleaning up intel_dp_hpd_pulse"). I'm actually not sure why that was there. Perhaps to avoid an EDID read if the connector status didn't appear to change, but that sort of thing is quite racy and would have failed anyway if we failed to keep up with the hotplugs (if we missed the HPD down in between two HPD ups). And now that we take this codepath unconditionally we definitely need to drop the goto as otherwise we would never do the EDID read.

v2: Drop the goto that made us skip EDID reads entirely. Doh!
v3: Rebase due to locking changes
s/apparely/apparently/ in the comment (Chris)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99766
References: https://lists.freedesktop.org/archives/intel-gfx/2017-February/119779.html

index 6e04cb54e3ff..ee77b519835c 100644
@@ -4636,9 +4636,20 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 		 */
 		status = connector_status_disconnected;
 		goto out;
-	} else if (connector->status == connector_status_connected) {
+	} else {
+		/*
+		 * If display is now connected check links status,
+		 * there has been known issues of link loss triggerring
+		 * long pulse.
+		 *
+		 * Some sinks (eg. ASUS PB287Q) seem to perform some
+		 * weird HPD ping pong during modesets. So we can apparently
+		 * end up with HPD going low during a modeset, and then
+		 * going back up soon after. And once that happens we must
+		 * retrain the link to get a picture. That's in case no
+		 * userspace component reacted to intermittent HPD dip.
+		 */
 		intel_dp_check_link_status(intel_dp);
-		goto out;
 	}
 
 	/*