Comment 5 for bug 1509326

11) Did a reboot because graphics performance had dropped. Reboot through XFCE desktop would make the screen go black, pstree showed that the desktop still lived. reboot command from console would work, but boot into a black screen (after a brief display of a background and something that might have been the mouse pointer). Closing and opening the lid would not help, detaching the laptop from the docking station and Ctrl-Alt-F7 would restore the XFCE desktop, reattaching to the docking station would give access to the docking-station-connected screens.
So... something wasn't properly initialized with the docking station attached during boot.

For reference, I have placed the following script on a hotkey to switch from laptop to docking-station-connected screens.

#! /bin/sh
echo ================================================== >>/home/jo/xrandr.log
echo docked.sh >>/home/jo/xrandr.log
date >>/home/jo/xrandr.log
echo >>/home/jo/xrandr.log
xrandr --output DP-6 --auto >>/home/jo/xrandr.log 2>&1
xrandr --output LVDS-0 --off >>/home/jo/xrandr.log 2>&1
xrandr --output DP-3 --auto --left-of DP-6 --primary >>/home/jo/xrandr.log 2>&1

It's extremely rigid and unable to deal with any variation in the hardware situation, and sometimes is fails to disable LVDS-0 and cannot activate DP-3 afterwards (I think because there are only two CRTCs), but if all hardware is properly detected, it will work reliably on the second attempt... barely good enough so I don't have to redo Display configuration every time it fails to auto-reconfigure when attaching to or detaching from the docking station.