A13 set backlight brightness on LCD

[mab]

Hi,
I'm trying to get the brightness settings working on a generic A13 tablet in Debian with a precompiled 3.0.57 kernel.

How do you dim the backlight from a running system on the OLinuXino LCD?

I couldn't find anything in /sys.
In script.bin there is some reference to lcd_pwm on port B2 (and lcd_bl_en) which seems to enable backlight globally, but nothing to set different levels.
dmesg gave "lcd_module_init" but no other hint.
I don't know how Android does it on these boards, maybe they are using some executable.
Do I need to load some module?
It seems strange to have the value hardcoded in the kernel.

What am I missing?