Backlight control for LCD screens

modulename: backlight.ko

and/or

via-pmu-backlight.ko

configname: CONFIG_PMAC_BACKLIGHT

Linux Kernel Configuration
└─>Device Drivers
└─>Macintosh device drivers
└─>Backlight control for LCD screens
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
Say Y here to enable Macintosh specific extensions of the generic
backlight code. With this enabled, the brightness keys on older
PowerBooks will be enabled so you can change the screen brightness.
Newer models should use a userspace daemon like pbbuttonsd.

source code:
arch/powerpc/platforms/powermac/backlight.c