@Konrad, thanks, that really looks like you spotted (and fixed) the problem.
I haven't tested your patch as I understand that my AGP card is quite old and I would not want to maintain a patched kernel just to be able to use it with KMS. My Xen box is a P4 and it's quite possible that not many users are still using hardware from that generation. If however, Ubuntu wants to integrate that patch I will happily test it.
@Konrad, thanks, that really looks like you spotted (and fixed) the problem.
I haven't tested your patch as I understand that my AGP card is quite old and I would not want to maintain a patched kernel just to be able to use it with KMS. My Xen box is a P4 and it's quite possible that not many users are still using hardware from that generation. If however, Ubuntu wants to integrate that patch I will happily test it.