linux-kernel - BUG: 4.10 i915 drm display noise regression

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Message-ID: <20170109063240.GB9125@shells.gnugeneration.com>
Date:   Mon, 9 Jan 2017 00:32:40 -0600
From:   lkml@...garu.com
To:     linux-kernel <linux-kernel@...r.kernel.org>
Cc:     dri-devel@...ts.freedesktop.org, chris@...is-wilson.co.uk
Subject: BUG: 4.10 i915 drm display noise regression - bisected to a6a7cc4b7

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@...is-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