This is a script to control screen brightness on Lenovo ThinkPad X220 and similar after you changed PWM frequency by writing a custom value to 0xC8254 register. I use it with acpid.
The script reads current PWM frequency from the register, calculates correct new brightness level for /sys/class/backlight/intel_backlight/brightness
and writes it.
To increase brightness:
write-intel-brightness +
To decrease:
write-intel-brightness -
From /etc/acpi/default.sh
on my Gentoo box:
case "$group" in
video)
case "$action" in
brightnessup)
/usr/local/bin/write-intel-brightness +
;;
brightnessdown)
/usr/local/bin/write-intel-brightness -
;;
esac
;;
esac
MIT