Public bug reported:

Sony Vaio P
Ubuntu Precise and Quantal
kernel 3.5.0
gma500_gfx kernel driver
modesetting xorg driver
Assume the current quantal & quantal-proposed versions of everything.

xbacklight doesn't work. No backlight change, and no output from the program.
"xbacklight" and "xbacklight -get" show nothing, no output from the program at 
all.
"xbacklight -set50" and "xbacklight-d :0 -set 50" does nothing nor prints any 
output.

However both sysfs and xrandr work fine.

Specifically:
xrandr --verbose lists outputs and shows the main screen has backlight property,
and "xrandr --output LVDS-0 --set backlight 50" changes the backlight 
brightness.

And

"cat /sys/class/backlight/psb-bl/actual_brightness" shows the current 
brightness, and
"echo 50 >/sys/class/backlight/psb-bl/brightness" changes the brightness.

I have written the following script to use in place of xbacklight:
http://forums.bodhilinux.com/index.php?/topic/5985-brightness-scripts/page__view__findpost__p__56911

This script, both the sysfs and xrandr methods of it, works fine for me on the 
same machine.
(for sysfs, I had to make a udev rule to allow users to write to the sysfs 
files, as noted on that page and in the --help output of the script)
It requires zenity for the user interactive options. Not needed for the 
non-interactive options.

-- 
bkw

** Affects: ubuntu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1054298

Title:
  xbacklight doesn't work, but xrandr does and so does
  /sys/class/backlight

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