(In reply to comment #23)
> Created attachment 102016 [details]
> dmesg from garbled display
Not sure if/why it's causing a garbled display, but I did spot one bug from the
log that's causing link retraining when it's not needed:

http://cgit.freedesktop.org/~darktama/nouveau/commit/?id=acc79e940a096657651980eb140176921a658e0c

> 
> The interesting thing here is that I waited for the dpms timeout, and the
> screen flashed and came back on more or less immediately, but clean.  It's
> as if something decided that the DPMS-off transition was "activity" and
> turned the screen back on, properly this time.  I don't think that's a
> driver issue though.

I hope this is just the monitor being really confused as a result of whatever
went wrong before it.  If it's not, your monitor is doing the wrong thing and
it's going to cause it to immediately resume from a power off (we can work
around the problem if it's necessary).  But, in your log, your monitor is
saying "help! i lost the link! retrain me!" in response to DP_SET_POWER_D3,
which it is *explicitly* (according to the DP spec, and, well, common sense)
not supposed to do.