[Intel-gfx] 3.0 (or SNA?) regression: failed to train DP, aborting

[Keith Packard]

On Mon, 25 Jul 2011 13:15:54 -0400, Andrew Lutomirski <luto at mit.edu> wrote:

> Done.

Jesse Barnes and I discovered, much to our horror, that the hotplugging
path isn't holding the struct mutex while attempting to retrain the DP
link. That means that an application could well be doing a bit of
overlapping modesetting fun. And, it seems like the trace you provided
shows precisely that happening.

Care to try this patch? It's fixed my persistent hot-unplug problems.

From bba6ccca57f0536fb5aae278527939d7247a1f53 Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp at keithp.com>
Date: Mon, 25 Jul 2011 10:04:56 -0700
Subject: [PATCH] drm/i915: Hold struct_mutex during hotplug processing

Hotplug detection is a mode setting operation and must hold the
struct_mutex or risk colliding with other mode setting operations.

In particular, the display port hotplug function attempts to re-train
the link if the monitor is supposed to be running when plugged back
in. If that happens while mode setting is underway, the link will get
scrambled, leaving it in an inconsistent state.

Signed-off-by: Keith Packard <keithp at keithp.com>
---
 drivers/gpu/drm/i915/i915_irq.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 3b03f85..5fe8f28 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -306,12 +306,15 @@ static void i915_hotplug_work_func(struct work_struct *work)
 	struct drm_mode_config *mode_config = &dev->mode_config;
 	struct intel_encoder *encoder;
 
+	mutex_lock(&dev_priv->dev->struct_mutex);
 	DRM_DEBUG_KMS("running encoder hotplug functions\n");
 
 	list_for_each_entry(encoder, &mode_config->encoder_list, base.head)
 		if (encoder->hot_plug)
 			encoder->hot_plug(encoder);
 
+	mutex_unlock(&dev_priv->dev->struct_mutex);
+
 	/* Just fire off a uevent and let userspace tell us what to do */
 	drm_helper_hpd_irq_event(dev);
 }
-- 
1.7.5.4



-- 
keith.packard at intel.com
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