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

[bugzilla-daemon at freedesktop.org]

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

--- Comment #55 from Nathan Schulte <nmschulte at gmail.com> ---
I've completed the bisection, and git points to this commit as being the
one that resolves the issue:

commit 0b9f43a0ee7e89013a3d913ce556715fd8acb674
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Tue Jun 5 10:07:11 2012 +0200

    drm/i915: allow pipe A for lvds on gen4

    Given the havoc the missing backlight pipe select code might have
    caused, let's try to re-enabled pipe A support for lvds on gen4 hw.
    Just to see what all blows up ...

    Note though that

    commit 4add75c43f39573edc884d46b7c2b7414f01171a
    Author: Chris Wilson <chris at chris-wilson.co.uk>
    Date:   Sat Dec 4 17:49:46 2010 +0000

        drm/i915: Allow LVDS to be on pipe A for Ironlake+

    claims that this caused tons of spurious wakeups somehow.

    More details can be found in the old revert:

    commit 12e8ba25ef52f19e7a42e61aecb3c1fef83b2a82
    Author: Chris Wilson <chris at chris-wilson.co.uk>
    Date:   Tue Sep 7 23:39:28 2010 +0100

        Revert "drm/i915: Allow LVDS on pipe A on gen4+"

        Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=16307

    Reviewed-by: Eugeni Dodonov <eugeni.dodonov at intel.com>
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

I've attached the bisect log, including marking the final commit (should
you wish to replay the log, you will probably need to remove this
entry).

Given the nature of the bug, appearing to be a race condition and not
always easily reproducible, I booted each kernel (I built it nearly 40
times in all) until I either experience the black screen, or about 5-10
times until I was satisfied it was not occurring, with the latter builds
receiving more scrutiny.  I have booted this "fix" commit many, many
times and have yet to experience the issue, where as the commit before
had the issue after the second boot.

It should be noted that this commit immediately follows some that appear
to modify backlight operation for gen4.  It should also be noted that my
particular controller, on an Dell Vostro 1510, is as follows:

00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile
GM965/GL960 Integrated Graphics Controller (primary) [8086:2a02] (rev
0c) (prof-if 00 [VGA controller])
    Subsystem: Dell Device [1028:0273]
    Flags: bus master, fast devsel, latency 0, IRQ 47
    Memory at f8000000 (64-bit, non-prefetchable) [size=1M]
    Memory at d0000000 (64-bit, prefetchable) [size=256M]
    I/O ports at 1800 [size=8]
    Expansion ROM at <unassigned> [disabled]
    Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
    Capabilities: [d0] Power Management version 3
    Kernel driver in use: i915

Lastly, these commits appear to be merged into mainline at the v3.6-rc1
release, and came after the v3.4 release.  I am experiencing the blank
screen issue with a Debian 3.2 kernel, and a Debian 3.7 kernel.  Looking
at the source for the Debian 3.2 kernel, I do not see this change; there
is no check for GEN4 and setting the pipe A mask (the lsb; (1 << 0)),
and the catchall else only sets pipe B (bit 1; (1 << 1)).  Looking at
the source for the Debian 3.7 kernel, the change is visible.

So, we've got conflicting data... Perhaps there is some issue with
modesetting and checking the crtc_mask properly?  I could look at that
code if needed.  It's also possible I have no idea what I'm talking
about.

Finally, I am in the process of frobbing the Debian 3.7 source to see
what happens.  I will share those results when I have them.  Again,
perhaps finding the actual regression (assuming the bug hasn't been
hidden all along with no actual regression) will shed some light.
Further, I'm thinking about looking into SVIDEO interactions with KMS,
as that appears to solve the issue.  I may also try downgrading my BIOS
and see what that effects, if possible.  Lots of places to go from here.

--
Nate

-- 
You are receiving this mail because:
You are the QA Contact for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/intel-gfx-bugs/attachments/20130113/fde6442a/attachment-0001.html>