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    SubjectRe: 3.13 i915 brightness settings broken when going from docked -> undocked
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    On Wed, Feb 19, 2014 at 9:20 PM, Josh Boyer <jwboyer@fedoraproject.org> wrote:
    > Hi All,
    >
    > We've had a rather weird report[1] of the brightness adjustments being
    > broken in a specific case with Thinkpad x220 hardware (SandyBridge
    > based). If you boot the machine with it in a dock and then undock,
    > the brightness adjustments do not work. That is with either the FN
    > keys or the GNOME brightness slider.
    >
    > I can see that the value of
    > /sys/class/backlight/acpi_video0/brightness increases/decreases but
    > /sys/class/backlight/intel_backlight/brightness doesn't reflect any
    > changes. With 3.12 this works, and oddly with 3.14-rc1 it works
    > (specifically, it starts working around v3.13-10231-g53d8ab2 which is
    > right after the first DRM merge for 3.14). With 3.13, if I undock and
    > echo a higher value in the intel_backlight_brightness sysfs entry, the
    > brightness will actually increase so it can be done manually, but it
    > does not work as you'd expect.
    >
    > I'm in the middle of trying to do a reverse bisect for which patch
    > fixes it in the 3.14-rcX series, but that's taking a while. I thought
    > I'd email and see if anyone already knows about this situation, what
    > patch in 3.13 broke this, and which one then fixed it again. Thus far
    > all I've gathered is that backlight handling is confusing.

    The reverse bisect between 3.13 and 3.14-rc1 didn't prove fruitful,
    either because I messed it up or there's a combination of things that
    fix the issue. So instead I did a regular git bisect between 3.12 and
    3.13 to see which commit _broke_ things and caused the above behavior.
    That landed me at:

    Author: Jesse Barnes <jbarnes@virtuousgeek.org>
    Date: Thu Oct 31 18:55:49 2013 +0200

    drm/i915: make backlight functions take a connector

    I have no idea if that makes sense or not, but it's at least something
    that seems to be in a relevant area of code. Does anyone involved in
    that know why it would cause the above symptoms on 3.13, and which
    commit(s) fix it in 3.14-rc1?

    josh


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