[Intel-gfx] external screen goes black

[Jonathan Adamczewski]

Hardware is a Dell XPS laptop, xorg log reports "Integrated Graphics
Chipset: Intel(R) Sandybridge Mobile (GT2)"

Running a custom configured 3.7.2 based kernel, xf86-video-intel-2.20.17.

I'm running the internal LVDS screen at 1080p and a Dell 2713HM monitor at
2560x1440 connected via display port.

Both screens run fine when X starts, but at some point the external monitor
will go black. The system doesn't recognize it as being disconnected - no
KDE popup asking if I want to change the monitor config as happens when
pulling the DP or power on the monitor.

Sometimes it will return to life after a short amount of time, most of the
time it stays black indefinitely. A full power cycle of the monitor
(pulling the plug) will usually bring it back to life, but typically not
for long.

The screen usually goes black while there's a high degree of display
activity - a video playing, moving large windows around the screen, looking
around in google streetview, etc. It doesn't seem to matter which screen
the activity is on.

It *seems* to be less likely if I run the external display at a lower
resolution.

There's nothing that coincides with the screen going black in dmesg or the
xorg log.

I've had no problems with this monitor under Windows 7 (gaming, videos,
etc).

What I'm looking for: ideally a simple fix :) Otherwise, any suggestions
about where to look to gather more information on what could be happening
here - or other places to ask for help.

Many thanks

jonathan.
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