[Bug 320874] [NEW] [asus] /sys/devices/virtual/backlight/acpi_video0/brightness has it backwards

Khashayar Naderehvandi khashayar.lists at gmail.com
Sat Jan 24 16:38:38 UTC 2009

Public bug reported:

>From the upstream bug report:
"Hardware Environment:
Asus, N20A, all intel.

Problem Description:
If the laptop loads the video module at boot time,
/sys/devices/virtual/backlight/acpi_video0/brightness is created. However, it's
all backwards, confusing applications like gnome-power-manager and the likes
(well, that basically means hal). Echoing 0 to 'brightness' raises the
backlight of this laptop to maximum. Echoing 13 to it, takes the backlight to a
actual_brightness' seems to stay at 0 at all times.

If I disallow the video module to be loaded at boot time, there's no backlight
interface in /sys/class/backlight/*. But, nevertheless, the xbacklight utility
and hal seem to be able to control the backlight just fine. In this latter
case, withouth the video module loaded, xbacklight & hal handle the backlight
correctly, i.e. less means lower backlight, and more means brighter backlight."

More info in the upstream bug report, which I filed some time ago. It's
fixed in mainline for 2.6.29, but won't be backported to vanilla. I
think Ubuntu should include it, however, as it's a major annoyance and


** Affects: linux
     Importance: Unknown
         Status: Invalid

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

** Bug watch added: Linux Kernel Bug Tracker #12235

** Also affects: linux via
   Importance: Unknown
       Status: Unknown

** Summary changed:

- /sys/devices/virtual/backlight/acpi_video0/brightness has it backwards
+ [asus] /sys/devices/virtual/backlight/acpi_video0/brightness has it backwards

[asus] /sys/devices/virtual/backlight/acpi_video0/brightness has it backwards
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