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SubjectRe: Skylake graphics regression: projector failure with 4.8-rc3
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On Wed, 2016-08-31 at 11:23 -0700, James Bottomley wrote:
> 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.

After more playing around, I'm getting thousands of these in the kernel
log (possibly millions: the log wraps very fast):

[23504.873606] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to train DP, aborting

And then finally it gives up with

[25023.770951] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
[25561.926075] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun

And the crtc for the VGA output becomes non-responsive to any
configuration command. This requires a reboot and sometimes a UEFI
variable reset before it comes back.

James

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