xbacklight doesn't do anything, not even error message.

[Brian K. White]

gma500, kernels 3.2.0, 3.5.0, and 3.6.0

Currently:
bkw@noexcuse:~$ uname -a
Linux noexcuse 3.6.0-030600-generic #201209302035 SMP Mon Oct 1 00:43:10 UTC 2012 i686 i686 i686 GNU/Linux

bkw@noexcuse:~$ lsmod |grep gma
gma500_gfx 198198 2
drm_kms_helper 45427 1 gma500_gfx
drm 227730 3 gma500_gfx,drm_kms_helper
i2c_algo_bit 13316 1 gma500_gfx
video 18908 1 gma500_gfx

bkw@noexcuse:~$ dpkg-query -W xserver-xorg
xserver-xorg 1:7.7+1ubuntu3

xbacklight and enlightenment 17 backlight module don't do anything.

xbacklight doesn't even output an error message or anything no matter what command line options are used.

However, both of these two things DO work:

echo 75 > /sys/class/backlight/psb-bl/brightness
and
xrandr --output LVDS-0 --set backlight 75

For me, there is also a /sys/class/backlight/acpi_video0/brightness which only takes values from 0-8 and which does not work.

Also, for me, setting "acpi_backlight=vendor" on the grub command line results in there not being a /sys/class/backlight/psb-bl/ directory any more, instead in it's place there is /sys/class/backlight/sony or maybe it was sonypi , but it works the same as psb-bl. It didn't make xbacklight start working nor e17's backlight module. xrandr and sysfs (under the new name) both still worked the same.

As a work-around I wrote and am using this in the meantime:
http://code.google.com/p/bltool/