[Intel-gfx] External output completely broken on Skylake (hard freeze)?

[Oskar Berggren]

Hi,

My laptop seem to work ok with the internal display (though I haven't used
it extensively yet).

When I connect an external monitor it's being recognized and show up in
xrandr, but I get severe "animated" distortion on the _internal_ panel.
Sometimes the distortion doesn't happen until i move the mouse slightly.
Sometimes I can make it stop briefly by pressing a key on the keyboard.
After a few seconds the computer completely stops responding (not even
ping). Continous kernel log over SSH show  "FIFO underrun" at the time the
external monitor is connected, but nothing at the time of the hang.

Is this (likely to be) a known problem and I should just wait a bit, or is
it worthwhile to try to debug? I know about "drm.debug=0x1e log_buf_len=1M"
- anything else that could be helpful? What would be the best way to detect
what happens right at the crash, since so far I get nothing in dmesg. At
least nothing I can retrieve.


System is Dell XPS 15 9550, i7-6700HQ, stepping 3, microcode 0x74.
Fedora 23 plus kernel drm-intel-nightly as of 2016-03-10 21:00 UTC.

Internal panel is eDP1, 3840x2160.

External is 1920x1200. I've tried the HDMI port, and also with a TB3->DP
and TB3->HDMI adapters, all with same results.


Regards,
Oskar
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