Please start you kernel with thinkpad_acpi compiled as module and post results of falowing commands:
modprobe -c | grep think lsmod | grep think ls -l /proc/acpi/ibm/brightness
Please start you kernel with thinkpad_acpi compiled as module and post results of falowing commands:
modprobe -c | grep think ibm/brightness
lsmod | grep think
ls -l /proc/acpi/