BUG: 4.10 i915 drm display noise regression - bisected to a6a7cc4b7

[lkml at pengaru.com]

Hello all,

I'm experiencing display noise in the form of 8x1 pixel bars spuriously
appearing in random locations.  This doesn't happen on 4.9, the machine
is an X61s, a Core2Duo 1.8Ghz w/XGA via LVDS.

I was able to bisect the issue to a6a7cc4b7:

commit a6a7cc4b7db6deaeca11cdd38844ea147a354c7a
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Fri Nov 18 21:17:46 2016 +0000

    drm/i915: Always flush the dirty CPU cache when pinning the scanout
    
    Currently we only clflush the scanout if it is in the CPU domain. Also
    flush if we have a pending CPU clflush. We also want to treat the
    dirtyfb path similar, and flush any pending writes there as well.
    
    v2: Only send the fb flush message if flushing the dirt on flip
    v3: Make flush-for-flip and dirtyfb look more alike since they serve
    similar roles as end-of-frame marker.

Reproduction is simple, just run this native drm eye candy program:
https://github.com/vcaputo/rototiller

Thanks,
Vito Caputo