I just tried this with kernel 3.13.0-34.60 and I'm still experiencing the problem. Brightness set to minimum and not adjustable after undocking.
I originally encountered another (duplicate?) bug post which suggested to upgrade the x220's BIOS, so I'm also running the latest BIOS version (8DET69WW / 1.39). The possible duplicate is at https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1348550?comments=all
I just tried this with kernel 3.13.0-34.60 and I'm still experiencing the problem. Brightness set to minimum and not adjustable after undocking.
I originally encountered another (duplicate?) bug post which suggested to upgrade the x220's BIOS, so I'm also running the latest BIOS version (8DET69WW / 1.39). The possible duplicate is at https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/1348550? comments= all