[Bug 92565] New: Extra ("phantom") display

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=92565

            Bug ID: 92565
           Summary: Extra ("phantom") display
           Product: xorg
           Version: 7.7 (2012.06)
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/intel
          Assignee: chris at chris-wilson.co.uk
          Reporter: monnier at iro.umontreal.ca
        QA Contact: intel-gfx-bugs at lists.freedesktop.org

I just got a new Thin-ITX board (Asus H81T) with a Core i3-4170, and I get an
annoying problem: I have a single monitor connected to this machine, using the
DVI connection, yet X11 thinks there are two monitors:

    % xrandr
    Screen 0: minimum 320 x 200, current 1920 x 1200, maximum 8192 x 8192
    VGA1 disconnected (normal left inverted right x axis y axis)
    HDMI1 disconnected (normal left inverted right x axis y axis)
    HDMI2 connected primary 1920x1200+0+0 (normal left inverted right x axis y
axis) 546mm x 352mm
       1920x1200     59.95*+
       1600x1200     60.00  
       1680x1050     59.88  
       1280x1024     75.02    60.02  
       1440x900      59.90  
       1280x960      60.00  
       1152x864      75.00  
       1024x768      75.08    70.07    60.00  
       832x624       74.55  
       800x600       72.19    75.00    60.32    56.25  
       640x480       75.00    72.81    66.67    60.00  
       720x400       70.08  
    DP1 connected (normal left inverted right x axis y axis)
       1024x768      60.00  
       800x600       60.32    56.25  
       848x480       60.00  
       640x480       59.94  
    HDMI3 disconnected (normal left inverted right x axis y axis)
    %

This is the output after I manually turned the DP1 display off.  In the BIOS
I'm offered some options about the internal LVDS connection, and the above
output is what I get when this option says "disabled".  If I enable this
option, then I don't get this DP1 output but get an eDP1 output instead, with
the same problem except made worse because this eDP1 output is then marked as
"primary" which forces me to do all kinds of gymnastics in order to actually
get to see the login screen.

How can I get rid of this "phantom" display?  Also, FWIW, I get the impression
that this also affects the Linux console, since it doesn't use up all my
monitor (I'd estimate that it only uses the 1024x768 top-left portion of it).

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