[Intel-gfx] Skylake graphics regression: projector failure with 4.8-rc3

[James Bottomley]

On Fri, 2016-08-26 at 09:10 -0400, James Bottomley wrote:
> 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.

I'm home now.  Unfortunately, my monitor isn't as problematic as the
projector, but by flipping between various modes and separating and
overlaying the panels with --above and --same-as (xrandr), I can
eventually get it to the point where the main LCD panel goes black and
can only be restarted by specifying a different mode.

This seems to be associated with these lines in the X

[ 14714.389] (EE) intel(0): failed to set mode: Invalid argument [22]

But the curious thing is that even if this fails with the error message
once, it may succeed a second time, so it looks to be a transient error
translation problem from the kernel driver.

I've attached the full log below.

This is only with a VGA output.  I currently don't have a HDMI dongle,
but I'm in the process of acquiring one.

James
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