[Intel-gfx] [PATCH] drm/i915: Resume DP MST before doing any kind of modesetting

Lyude cpaul at redhat.com
Tue Feb 23 22:11:52 UTC 2016

As it turns out, resuming DP MST is racey since we don't make sure MST
is ready before we start modesetting, it just usually happens to be
ready in time. This isn't the case on all systems, particularly a
ThinkPad T560 with displays connected through the dock. On these
systems, resuming the laptop while connected to the dock usually results
in blank monitors. Making sure MST is ready before doing any kind of
modesetting fixes this issue.

We originally changed the resume order in

	commit e7d6f7d70829 ("drm/i915: resume MST after reading back hw state")

to fix a ton of WARN_ON's after resume, but this doesn't seem to be an
issue now anyhow.

CC: stable at vger.kernel.org
Signed-off-by: Lyude <cpaul at redhat.com>
 drivers/gpu/drm/i915/i915_drv.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index f357058..4dcf3dd 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -733,6 +733,14 @@ static int i915_drm_resume(struct drm_device *dev)
+	/*
+	 * We need to make sure that we resume MST before doing anything
+	 * display related, otherwise we risk trying to bring up a display on
+	 * MST before the hub is actually ready
+	 */
+	intel_dp_mst_resume(dev);
@@ -765,8 +773,6 @@ static int i915_drm_resume(struct drm_device *dev)
-	intel_dp_mst_resume(dev);
 	 * ... but also need to make sure that hotplug processing
 	 * doesn't cause havoc. Like in the driver load code we don't

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