Comment 129 for bug 745112

> xrandr --output DP1 --set audio off

looks good:

I plugged my laptop into the dock, and it came up at the medium
resolution it was running at earlier in the day. I ran that command,
and the screen blanked briefly, I guess while the dp link was
reestablished. I then used the displays panel to switch up to full
resolution and it worked.

So, 1/1. But, this has always been a bit intermittent, so more
testing might be needed.