backlight regression on ASUS F6S: inverted brightness control

[Kel Modderman <kel@otaku42.de>]

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Hi,

After booting Linux 2.6.28 the backlight control actions have now reversed,
ie: attempting to make backlight brighter makes it dimmer and vice versa.

The recent backlight changes (video vs. vendor) seem to have the result of
allowing the ASUS F6S backlight hardware be driven via the acpi/video driver
rather than the vendor/asus_laptop driver as per printk:

asus-laptop: Brightness ignored, must be controlled by ACPI video driver

Linux < 2.6.28
--------------
# cat /sys/class/backlight/asus-laptop/max_brightness
15

# Makes backlight brightest
# echo 15 > /sys/class/backlight/asus-laptop/brightness

# Makes backlight dimmest
# echo 0 > /sys/class/backlight/asus-laptop/brightness

Linux = 2.6.28
--------------
# cat /sys/class/backlight/acpi_video0/max_brightness
13

# Makes backlight brightest
# echo 0 > /sys/class/backlight/acpi_video0/brightness

# Makes backlight dimmest
# echo 13 > /sys/class/backlight/acpi_video0/brightness


A search for "linux 2.6.28 backlight" led to an Ubuntu bug report [1] which
describes an ASUS notebook user with the same situation.

[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/305935

Is it possible to have the ACPI video driver to behave correctly on this
hardware?

I'd like to provide any further required information. I've attached a bzip
tarball containing:
  /sys/devices/platform/asus-laptop/infos
  /proc/acpi/dsdt
  dmesg output
  dmidecode output

Thanks, Kel.

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