[Bug 70791] New: [HSW ULT]eDP brightness is zero after the computer start

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=70791

          Priority: medium
            Bug ID: 70791
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: [HSW ULT]eDP brightness is zero after the computer
                    start
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: qingshuai.tian at intel.com
          Hardware: All
            Status: NEW
           Version: unspecified
         Component: DRM/Intel
           Product: DRI

Created attachment 88022
  --> https://bugs.freedesktop.org/attachment.cgi?id=88022&action=edit
dmesg (its brightness can changed by the function keys)

System Environment:
--------------------------
Kernel: (drm-intel-next-queued)d538bbdfde34028b5c5b0ba92b3c2096c5afb82c
Author: Damien Lespiau <damien.lespiau at intel.com>
Date:   Mon Oct 21 14:29:30 2013 +0100

Bug detailed description:
-----------------------------
Everytime when the computer boot up into operating system, its eDP monitor will
turn into black and its brightness is zero. But in the BIOS stage, the monitor
works well.

After the machine boot up, we can change the brightness with the function
keys(Fn+F11),or we can also change the value of brightness in file
(/sys/class/backlight/intel_backlight/brightness) .Then the monitor will work
normally.

But sometime the function keys doesn't work, and I can't find the
file(/sys/class/backlight/intel_backlight/brightness). This occured once out of
every two times.

Reproduce steps:
-----------------------------
1.boot up the machine 
2.cat /sys/class/backlight/intel_backlight/brightness

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