[Bug 72976] New: Brightness control becomes binary after suspend on haswell

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=72976

          Priority: medium
            Bug ID: 72976
          Assignee: chris at chris-wilson.co.uk
           Summary: Brightness control becomes binary after suspend on
                    haswell
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: lionel.g.landwerlin at linux.intel.com
          Hardware: Other
            Status: NEW
           Version: unspecified
         Component: Driver/intel
           Product: xorg

I'm using Linux on my macbook air 2013 (haswell) (using Debian).
After a suspend cycle, the brightness will just go binary, full brightness for
the 91-100%, and then completely blank under 91%.

I've noticed the behavior while using Gnome, then tried to reproduce 
by poking at
/sys/devices/pci0000:00/0000:00:02.0/backlight/acpi_video0/brightness directly.

Then I tried poking at
/sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight/brightness
where the range is 0-2777. And I found the same kind of behavior, except that
at the values 2303/2304, the screen would just keep going up/down in brightness
without any interection on the /sys interface. Otherwise 2302 and below would
be blank and 2305 and above would be full brightness 

It's using the following relevant components :

 xserver-xorg 7.7+4 
 xserver-xorg-video-intel 2.21.15-1+b2
 kernel 3.12.3

I guess the bug is more likely to be somewhere in the kernel than in the X
driver.

Folks have reported the bug in other places already :

https://bugzilla.redhat.com/show_bug.cgi?id=989555

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1197482

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