I was under the impression that libata pata and ide drivers are mutually exclusive. You're not supposed to be using both at the same time unless they're for completely different controllers.Very strange trace indeed. I'll take a look at this. At least since it
came from Qemu I should be able to "build" a suitable PC to match yours.
Original Intel PIIX devices are handled by "OLDPIIX" (0x8086, 0x1230).
The later ones by ata_piix. The only oddity I see is that you have no
PCI bus mastering address base assigned (bmdma)
I also tried VMWare 5.5 that emulated PIIX4. It works if I only put ata_piix driver in. With the same kernel that Qemu gets the error, VMWare gets another oops during generic ide initialisation. I relooked and found that I have both generic PCI ide and generic ISA ide drivers compiled in, so I disabled them and it works using ata_piix (with PATA and ATAPI enabled). Even ATAPI cdrom worked as the root partition.
But, the different oops that I got in vmware with generic ide:
http://www.cs.ut.ee/~mroos/atacrash.png