[Bug 73694] [hsw DP] Ubuntu 12.04 unable to use external monitor through edock

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=73694

--- Comment #24 from Michael Thayer <m.j.thayer at gmail.com> ---
I am seeing something very much like this on a Dell Lattitude E7440 with an old
EPort Plus docking station and an external 1920x1200 monitor attached to the
first DVI connector.  xrandr output below.  I am running Ubuntu 14.04 with the
Ubuntu kernel team 3.15.8-031508-generic build.  Quite often, after boot-up or
after the screen saver has run the external monitor is shown by xrandr but
remains black, and I see "*ERROR* failed to train DP, aborting" in the dmesg
output.  Usually undocking and re-docking the laptop once or twice makes the
external display come back on.

I am attaching a dmesg log with drm.debug=0xe when the problem occurred shortly
after boot, and a second containing the additional messages shown after I
undocked and re-docked the laptop once, restoring the display.

$ xrandr
Screen 0: minimum 320 x 200, current 3840 x 1200, maximum 32767 x 32767
eDP1 connected primary 1920x1080+1920+0 (normal left inverted right x axis y
axis) 309mm x 173mm
   1920x1080      60.0*+   59.9  
   1680x1050      60.0     59.9  
   1600x1024      60.2  
   1400x1050      60.0  
   1280x1024      60.0  
   1440x900       59.9  
   1280x960       60.0  
   1360x768       59.8     60.0  
   1152x864       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
HDMI1 disconnected (normal left inverted right x axis y axis)
DP1 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x
324mm
   1920x1200      59.6*+
   1920x1080      60.2  
   1600x1200      60.1  
   1280x1024      76.0     75.0     60.0  
   1152x921       66.0  
   1152x864       75.0  
   1024x768       75.1     75.0     70.1     60.0  
   832x624        74.6  
   800x600        72.2     75.0     60.3     56.2  
   640x480        75.0     72.8     66.7     60.0  
   720x400        70.1  
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

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