[Bug 53541] New: GM45 regression in commit: 0b9f43a drm/i915: allow pipe A for lvds on gen4

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=53541

           Summary: GM45 regression in commit: 0b9f43a drm/i915: allow
                    pipe A for lvds on gen4
           Product: Drivers
           Version: 2.5
    Kernel Version: 3.6
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - Intel)
        AssignedTo: intel-gfx-bugs at lists.freedesktop.org
        ReportedBy: paran at lysator.liu.se
                CC: intel-gfx-bugs at lists.freedesktop.org
        Regression: Yes


With kernel 3.6 and later X is unusable on a Lenovo x200s laptop.

Good kernel versions: 3.5.0, 3.5.7
Bad kernel versions: 3.6.11, 3.7.6, 3.8.0-rc6

Distributions is Ubuntu 12.04. All tested kernels are built from
mainline and stable git.

x200s have an Intel GMA45 GPU:
$ lspci|grep VGA
00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset
Integrated Graphics Controller (rev 07)

A rather non-technical description of the bug is that the screen does
not seem to be refreshed as often as it should be. For example when
typing a password into the KDM login window, no * characters are
shown. In konsole (KDEs terminal emulator) the window content
frequently freezes. I can keep on typing and running commands, but
nothing changes on the screen until I change back and forth between
either another konsole tab or another virtual desktop.

I have bisected this and the first bad commit is:

commit 0b9f43a0ee7e89013a3d913ce556715fd8acb674
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   2012-06-05 10:07:11 +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 ...
...snip...

So I guess one thing that blows up is my laptop? Reverting this commit
fix the problem for me, verified on 3.6.11 and 3.8.0-rc6.

Please let me know if I can help debug this further.

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