After a long struggle, we finally traced down the cause of the X lockups when using the -psb driver with ubuntu-mobile on the Menlow boxes. I was actually a bit surprised that the system booted up!
Essentially, the code was creating two locks via psbDRILock(). For some reason, this works okay on Gutsy, but leads to this lockup on Hardy. After commenting out the second Lock/Unlock, X came up and seems to be working fine.
Looking at the Xorg.0.log, it is definitely running with the psb driver, and the log contains nothing unexpected. (There are some error and warning messages, but nothing we don't already know about.)
So, since this seems to solve the issue (at least for the present), I've uploaded the fixed -psb to Ubuntu Mobile PPA.
I played around with some apps, and everything seems to be working fine. 3D performance is poor, but that's expected since we don't have the 3D driver yet. However, glxgears runs, it's just slow (10.5 fps).
