Comment 9 for bug 1320659

I also have this problem. I am using Ubuntu 14.04 64 bit with a Thinkpad T440S.

At the beginning, I have the following four problems:

1. After every boot, the brightness is set to maximum.
2. The brightness can't be adjusted smoothly. Only 4 brightnesses can be achieved with Fn keys.
3. After recovering from dimming, the brightness is set to maximum.
4. The following error message is printed during the boot:
[ 12.843633] thinkpad_acpi: Unsupported brightness interface, please contact <email address hidden>

The following workaround fixes 1 for me.
http://askubuntu.com/questions/151651/brightness-is-reset-to-maximum-on-every-restart

I add "acpi_backlight=vendor" kernel parameter according to https://wiki.ubuntu.com/Kernel/Debugging/Backlight. This fixes 2 and 3 for me.

But 4 still exists.