[Bug 47941] [snb] Backlight control broken between 3.6.0-rc1 and 3.6.0-rc4

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=47941


Tony Houghton <h at realh.co.uk> changed:

           What    |Removed                     |Added
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                 CC|                            |h at realh.co.uk




--- Comment #51 from Tony Houghton <h at realh.co.uk>  2013-03-15 23:02:25 ---
Since upgrading to kernel 3.8 the display on my Samsung NP900X3C won't resume
from sleep. I can enable it again by restarting gdm3 with ssh, but I can't find
a way to recover without having another PC handy. FWIW this model is notorious
for broken ACPI behaviour, and in earlier kernels closing the lid often fails
to make it sleep, and it never resumes just by opening the lid, you have to
press the power button.

I came here via git bisect:

cf0a6584aa6d382f802f2c3cacac23ccbccde0cd is the first bad commit
commit cf0a6584aa6d382f802f2c3cacac23ccbccde0cd
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Wed Feb 6 11:24:41 2013 +0100

    drm/i915: write backlight harder

    770c12312ad617172b1a65b911d3e6564fc5aca8 is the first bad commit
    commit 770c12312ad617172b1a65b911d3e6564fc5aca8
    Author: Takashi Iwai <tiwai at suse.de>
    Date:   Sat Aug 11 08:56:42 2012 +0200

        drm/i915: Fix blank panel at reopening lid

    changed the register write sequence for restoring the backlight, which
    helped prevent non-working backlights on some machines. Turns out that
    the original sequence was the right thing to do for a different set of
    machines. Worse, setting the backlight level _after_ enabling it seems
    to reset it somehow. So we need to make that one conditional upon the
    backlight having been reset to zero, and add the old one back.

    Cargo-culting at it's best, but it seems to work.

    Cc: stable at vger.kernel.org
    Cc: Takashi Iwai <tiwai at suse.de>
    Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=47941
    Reviewed-by: Jani Nikula <jani.nikula at intel.com>
    Acked-by: Takashi Iwai <tiwai at suse.de>
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

:040000 040000 3a65de0b75b23cc30f2d8d0fe90304ca2302fbfa
ec984a40be2c47943aa202094b7ce224ff7e8ef7 M    drivers

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