Tibet, the eternal problem with the permit

Hi mates
I'm in Korea right now, intend to leave within the next weeks, over to China, bound for Chengdu, further west, towards Lhasa.
Questions:
Does anybody know about the current situation about the permits? Where are the checkpoints located exactly? True, that Chinese PSB tries to crackdown on illegal cyclists in Tibet intensively this year?
Anybody with similar plans?
Thanks , seb.