[PATCH] drm/i915: Re-apply "Perform link quality check, unconditionally during long pulse"

[Jan-Marek Glogowski <glogow@fbihome.de>]

The same patch and various dmesg output is attached to
https://bugs.freedesktop.org/show_bug.cgi?id=107446 "Monitor on 2nd DisplayPort is not initialized"

I have no idea, if this patch is correct, but it fixes my problem of the "bricked" monitor.

Jan-Marek

---

From edf159ae0426d9c90bf974629d83dc50c002bc52 Mon Sep 17 00:00:00 2001
From: Jan-Marek Glogowski <glogow@fbihome.de>
Date: Fri, 3 Aug 2018 15:30:55 +0000
Subject: [PATCH] drm/i915: Re-apply "Perform link quality check
 unconditionally during long pulse"

This re-applies the workaround for "some DP sinks, [which] are a
little nuts" from commit 1a36147bb939 ("drm/i915: Perform link
quality check unconditionally during long pulse").
It makes the secondary AOC E2460P monitor connected via DP to an
acer Veriton N4640G usable again.

This hunk was dropped in commit c85d200e8321 ("drm/i915: Move SST
DP link retraining into the ->post_hotplug() hook")

Signed-off-by: Jan-Marek Glogowski <glogow@fbihome.de>
---
 drivers/gpu/drm/i915/intel_dp.c | 46 ++++++++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 153342c..796c2a2 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4294,18 +4294,6 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
 	return !drm_dp_channel_eq_ok(link_status, intel_dp->lane_count);
 }

-/*
- * If display is now connected check links status,
- * there has been known issues of link loss triggering
- * 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.
- */
 int intel_dp_retrain_link(struct intel_encoder *encoder,
 			  struct drm_modeset_acquire_ctx *ctx)
 {
@@ -4322,10 +4310,12 @@ int intel_dp_retrain_link(struct intel_encoder *encoder,
 	if (!connector || connector->base.status != connector_status_connected)
 		return 0;

-	ret = drm_modeset_lock(&dev_priv->drm.mode_config.connection_mutex,
-			       ctx);
-	if (ret)
-		return ret;
+	if (ctx) {
+		ret = drm_modeset_lock(
+			&dev_priv->drm.mode_config.connection_mutex, ctx);
+		if (ret)
+			return ret;
+	}

 	conn_state = connector->base.state;

@@ -4333,9 +4323,11 @@ int intel_dp_retrain_link(struct intel_encoder *encoder,
 	if (!crtc)
 		return 0;

-	ret = drm_modeset_lock(&crtc->base.mutex, ctx);
-	if (ret)
-		return ret;
+	if (ctx) {
+		ret = drm_modeset_lock(&crtc->base.mutex, ctx);
+		if (ret)
+			return ret;
+	}

 	crtc_state = to_intel_crtc_state(crtc->base.state);

@@ -4854,6 +4846,22 @@ intel_dp_long_pulse(struct intel_connector *connector)
 		 */
 		status = connector_status_disconnected;
 		goto out;
+	} else {
+		/*
+		 * If display is now connected check links status,
+		 * there has been known issues of link loss triggering
+		 * 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.
+		 */
+		struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
+
+		intel_dp_retrain_link(encoder, NULL);
 	}

 	/*
-- 
2.1.4
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