[Bug 95741] Broadwell graphics on Dell XPS13 (early 2015) loses horizontal sync on shift to tty console

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=95741

--- Comment #11 from W Unruh <unruh at physics.ubc.ca> ---
Very strange. I am doing a bisect now (I finally got it working, paring down
the modules etc so it now only takes 1/2 hour per compile. (there must be some
more efficient way to do it. ) I do not have any trouble with 3.19.0 so I am
narrowing it down to somewhere between that and 4.0 rc4. I will post when I
finish (I have about another 6 bisections to go.) I sure wish there were some
way to run the bisections so that only those modules/ files that had changed
got recompiled. But then I am doing the rpm-pkg, and it of course saves
nothing. 

So far I have (BISECT_LOG) 
git bisect start
# good: [bfa76d49576599a4b9f9b7a71f23d73d6dcff735] Linux 3.19
git bisect good bfa76d49576599a4b9f9b7a71f23d73d6dcff735
# bad: [13a7a6ac0a11197edcd0f756a035f472b42cdf8b] Linux 4.0-rc2
git bisect bad 13a7a6ac0a11197edcd0f756a035f472b42cdf8b
# good: [22aa66a3ee5b61e0f4a0bfeabcaa567861109ec3] dm snapshot: fix a possible
invalid memory access on unload
git bisect good 22aa66a3ee5b61e0f4a0bfeabcaa567861109ec3
# bad: [796e1c55717e9a6ff5c81b12289ffa1ffd919b6f] Merge branch 'drm-next' of
git://people.freedesktop.org/~airlied/linux
git bisect bad 796e1c55717e9a6ff5c81b12289ffa1ffd919b6f
# good: [9682ec9692e5ac11c6caebd079324e727b19e7ce] Merge tag
'driver-core-3.20-rc1' of
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core
git bisect good 9682ec9692e5ac11c6caebd079324e727b19e7ce
# good: [a9724125ad014decf008d782e60447c811391326] Merge tag 'tty-3.20-rc1' of
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty
git bisect good a9724125ad014decf008d782e60447c811391326
# bad: [f43dff0ee00a259f524ce17ba4f8030553c66590] Merge tag
'drm-amdkfd-next-fixes-2015-01-25' of
git://people.freedesktop.org/~gabbayo/linux into drm-next
git bisect bad f43dff0ee00a259f524ce17ba4f8030553c66590


Note that even with the later "good ones" ones, when I run "shut down computer" 
the brief vision of the text screen has a lost hsync  sometimes. This seems to
be sporadic.
When I test, I do alt-ctrl-Fx and then alt-ctrl-F1 to get back to X a number of
times (say 4)  and the result is always consistent (ie either lost hsync in the
tty, or it is fine). I do not see any horizontal flicker (I assume that means
in X, but I also do not see that in the tty console either).

Strange.

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