Comment 131 for bug 1308105

I also installed but my 2nd monitor doesn't come back on after it's entered power-save mode when I move the mouse which does turn my primary laptop display back on.

No combination of xrandr commands or switching to the console with CTRL-ALT-F1 brings it back on. The only thing that works is to power cycle the monitor which causes the display setup to switch back to single display mode. Then I have to go re-configure the dual display setup which is really annoying because I have to move all my windows back to their correct positions on the 2 displays.

I've tested my external monitor on windows and it always comes back on immediately even after entering the same power save mode so it's not an issue with the monitor.

Interestingly when I use the displayport over USB-C pass through it all works correctly. It's only with HDMI that the problem occurs.

I'm using a Dell Precision 5510 laptop with Intel Graphics enabled and the nvidia graphics disabled on Xubuntu 16.04.1 with all updates applied. I've also tested this with the same results on Ubuntu 16.10 with all updates applied.

xrandr shows it's still sending the signal to the external HDMI display even though the display is still in power saving mode:

tenpin: ~ xrandr
Screen 0: minimum 8 x 8, current 1920 x 2160, maximum 32767 x 32767
eDP1 connected 1920x1080+0+1080 (normal left inverted right x axis y axis) 346mm x 194mm
   1920x1080 59.93*+ 59.93
   1680x1050 59.95 59.88
   1600x1024 60.17
   1400x1050 59.98
   1600x900 60.00
   1280x1024 60.02
   1440x900 59.89
   1280x960 60.00
   1368x768 60.00
   1360x768 59.80 59.96
   1152x864 60.00
   1280x720 60.00
   1024x768 60.00
   1024x576 60.00
   960x540 60.00
   800x600 60.32 56.25
   864x486 60.00
   640x480 59.94
   720x405 60.00
   640x360 60.00
DP1 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
HDMI1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 527mm x 296mm
   1920x1080 60.00*+ 50.00 59.94
   1920x1080i 60.00 50.00 59.94
   1600x1200 60.00
   1280x1024 75.02 60.02
   1152x864 75.00
   1280x720 60.00 50.00 59.94
   1024x768 75.03 60.00
   800x600 75.00 60.32
   720x576 50.00
   720x576i 50.00
   720x480 60.00 59.94
   720x480i 60.00 59.94
   640x480 75.00 60.00 59.94
   720x400 70.08
HDMI2 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)