[Bug 94605] [SKL] Flashing black screen ([drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94605

--- Comment #109 from Paulo Zanoni <przanoni at gmail.com> ---
(In reply to Dominik Klementowski from comment #108)
> Yeah! The problem is gone for me with *only* patch 1. I have rc6 enabled and
> I haven't seen any flicker for whole day.
> Tested on Ubuntu 16.10 as well as current Arch Linux.
> Thanks once again. Hope this gets into official stable kernel soon.

Thanks a lot for testing this! We really appreciate that.

A little comment: so patch 1 prevents engine rings and FBC from being
initialized in the fist page of stolen memory, and then when the hardware
writes to it, it messes the contents of the ring or whatever else is there, and
on these things a single flipped bit can be a huge problem, so you see the
screen flickering.

Patch 2 prevents us from using the first page of stolen as a frontbuffer
inherited from the BIOS. The sort of corruption you'd see here would be
distortions in the very first line of pixels in your monitor, when we're using
that specific frontbuffer. I guess this is just way too hard to notice. But it
would be cool if you could confirm that :). With double-buffering and other
things it's probably going to be hard to spot this since not every frame will
show it, and even when you're on the correct buffer you may not see the
distortion or it  may be so small that you'll need really really good eyes to
notice it. But, still, my guess is that it's there :).

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