Aha, you have a 82855 hostbridge - I've seen 3 other people with that exact model hostbridge that also needed AGPMode 1. In at least one case, the user also reported that AGPMode 4 worked ok in windows, just not under ubuntu. You may be right that a more involved fix than a quirk is needed. I'll let upstream know.
Oops, thanks missed that lspci link.
Aha, you have a 82855 hostbridge - I've seen 3 other people with that exact model hostbridge that also needed AGPMode 1. In at least one case, the user also reported that AGPMode 4 worked ok in windows, just not under ubuntu. You may be right that a more involved fix than a quirk is needed. I'll let upstream know.