[Bug 75001] New: Brightness adjustment is broken in 945GM with kernel 3.14-rc2

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=75001

          Priority: medium
            Bug ID: 75001
                CC: intel-gfx-bugs at lists.freedesktop.org
          Assignee: intel-gfx-bugs at lists.freedesktop.org
           Summary: Brightness adjustment is broken in 945GM with kernel
                    3.14-rc2
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: luiorpe1 at gmail.com
          Hardware: x86 (IA32)
            Status: NEW
           Version: XOrg CVS
         Component: DRM/Intel
           Product: DRI

Created attachment 94098
  --> https://bugs.freedesktop.org/attachment.cgi?id=94098&action=edit
dmesg output 3.14-rc2 with drm.debug

First reported in the Linux kernel mailing list.

Laptop Model: Asus EeePC 1000H
Graphics: Intel 945GM

Testing the kernel version 3.14-rc2 I noticed adjusting the screen brightness
didn't work. The problem is already present in 3.14-rc1 whereas the 3.13 branch
works fine.

I first bisected the issue down to the following commit:
bc0bb9fd1c7810407ab810d204bbaecb255fddde drm/i915: remove
QUIRK_NO_PCH_PWM_ENABLE

However, given the concern that the bisection might be bogus I replayed it up
to the last 6 bisect steps. The issue was present in this bisect session and
this time I tracked it down to the commit:
b35684b8fa94e04f55fd38bf672b737741d2f9e2 drm/i915: do full backlight setup at
enable time

Hopefully this makes more sense.

Per request of the developers I've tested changing the brightness manually
through the sysfs. Here are the results.

ls -l /sys/class/backlight:
lrwxrwxrwx 1 root root 0 Feb 14 21:00 eeepc ->
../../devices/platform/eeepc/backlight/eeepc
lrwxrwxrwx 1 root root 0 Feb 14 20:59 intel_backlight ->
../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight


Linux 3.13.3: change the brightness manually:
Changing /sys/class/backlight/eeepc/brightness changes brightness and updates
the value.
changing /sys/class/backlight/intel_backlight/brightness changes brightness but
does NOT update the value. Always reports 156.

Linux 3.14-rc2: change the brightness manually:
changing /sys/class/backlight/eeepc/brightness does NOT change brightness but
updates the value.
changing /sys/class/backlight/intel_backlight/brightness changes brightness and
updates the value.


Finally I attach the following files:
dmesg.log

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