Tuesday, 18 February 2014

Secondary display not turning on after resume in linux

Occasionally my external display resisted to turn on after being re-plugged into laptop after suspend-resume cycle. The issue appeared again today, after I suspended laptop in the office and resumed it at home.

Tuning Display and Monitor in KDE Control Centre had no effect. Any attempts to turn on external display with xrandr failed silently or with error cannot find crtc for output.

Eventually, after playing around, noticed suspicious xrandr output

% xrandr
Screen 0: minimum 320 x 200, current 1440 x 1848, maximum 32767 x 32767
LVDS1 connected primary 1366x768+0+1080 (normal left inverted right x axis y axis) 277mm x 156mm
   1366x768       60.0*+
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected 1440x900+0+0 (normal left inverted right x axis y axis) # suspicious line

It appeared, that VGA1 output still remains kind of active, and laptop can only handle one external display at time.
Solution was as simple as this
% xrandr --output VGA1 --off