[Bug 53926] [945gm regression] LVDS boots to blank screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=53926

--- Comment #57 from Nathan Schulte <nmschulte at gmail.com> ---
Nathan Schulte wrote:
> I am bisecting at the moment to find the cause of the regression, as it
> doesn't appear obvious.  I assume it's got something to do with the
> recent KMS changes to i915.

fa55583797d12b10928a1813f3dcf066637caf5e is the first bad commit
commit fa55583797d12b10928a1813f3dcf066637caf5e
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Wed Oct 10 23:14:00 2012 +0200

    drm/i915: fixup the plane->pipe fixup code

    We need to check whether the _other plane is on our pipe, not
whether
    our plane is on the other pipe. Otherwise if not both pipes/planes
are
    active, we won't properly clean up the mess and set up our desired
    plane->pipe mapping.

    v2: Fixup the logic, I've totally fumbled it. Noticed by Chris
Wilson.

    v3: I've checked Bspec, and the flexible plane->pipe mapping is a
    gen2/3 feature, so test for that instead of PCH_SPLIT

    v4: Check whether we indeed have 2 pipes before checking the other
    pipe, to avoid upsetting i845g/i865g. Noticed by Chris Wilson.

    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=51265
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=49838
    Tested-by: Dave Airlie <airlied at gmail.com>
    Tested-by: Chris Wilson <chris at chris-wilson.co.uk> #855gm
    Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

This is the commit that introduced the bug into Debian's 3.7.1 kernel.
I believe this is also the cause of
https://bugs.freedesktop.org/show_bug.cgi?id=57365

Mainline 3.8-rc3 seems to be working fine.

Now what?

--
Nate

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