Some more info, if I load thinkpad_acpi with brightness_enable=1 set, I can control the brightness by echoing values into /proc/acpi/ibm/brightness. e.g.
echo level 10 > /proc/acpi/ibm/brightness
Some more info, if I load thinkpad_acpi with brightness_enable=1 set, I can control the brightness by echoing values into /proc/acpi/ ibm/brightness. e.g.
echo level 10 > /proc/acpi/ ibm/brightness