[PATCH] Intel, Dell, Ubuntu - i915/intel_dp.c

[Dragan Stancevic <dragan@lyktoree.com>]

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Hi,

this is not a patch for mainline. It affects Dell Precision M3800
Laptop running Ubuntu with Intel Graphics. Problem manifests in a way
where laptop after some use will not suspend anymore. It will attempt
to suspend, blank out the screen and come back up. It's rather finicky
as it doesn't happen consistently, but often enough that it started
being mildly annoying. I tracked it down to a race condition between
scheduled work and another thread. Essentially the driver would do a
double put on a structure if the race condition was hit. This patch
fixes the problem and my laptop has been suspending flawlessly for
about a month and a half.

- From my memory going back 1.5 months the race condition is between
_edp_panel_vdd_on, intel_edp_panel_off, edp_panel_vdd_off_sync.

Kernel and Distro info:
:~/src/Dell-M4800-Hardware/kernel$ uname -r
3.16.7-ckt8
:~/src/Dell-M4800-Hardware/kernel$ cat /etc/issue
Ubuntu 14.10 \n \l

Hope someone else finds the attached patch useful.

Thanks
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--- linux-3.16.0.ubt/drivers/gpu/drm/i915/intel_dp.c	2015-04-16 20:17:21.000000000 -0700
+++ linux-3.16.0/drivers/gpu/drm/i915/intel_dp.c	2015-04-16 20:29:45.040894002 -0700
@@ -1175,6 +1175,7 @@
 	if (!is_edp(intel_dp))
 		return false;
 
+	cancel_delayed_work(&intel_dp->panel_vdd_work);
 	intel_dp->want_panel_vdd = true;
 
 	if (edp_have_panel_vdd(intel_dp))