Skylake graphics regression: projector failure with 4.8-rc3

We seem to have an xrandr regression with skylake now. What's happening is that I can get output on to a projector, but the system is losing video when I change the xrandr sessions (like going from a - -above b to a --same-as b). The main screen goes blank, which is basically a reboot situation. Unfortunately, I can't seem to get the logs out of systemd to see if there was a dump to dmesg (the system was definitely responding).

I fell back to 4.6.2 which worked perfectly, so this is definitely some sort of regression. I'll be able to debug more fully when I get back home from the Linux Security Summit.

James