It shouldn't be that hard to add the latter though. seabios needs two more pci_region_type (PCI_REGION_TYPE_MEM_64 and PCI_REGION_TYPE_PREFMEM_64) to track and map 64bit bars separately. And a address space window where it can map 64bit bars to.
Right. This is a thing I'm thinking about now. I seems that the specifying 0x0 address in 64bit BARS is a bad idea. At least older versions of Linux just hang as soon as requested range does not fit in first 4GB. So the only option would be specifying the particular address range. It seems this works for everything - yet.
I wonder if there any particular reason to separate prefetchable a non-prefetchable memory regions in pciinit? Extra two more regions would make code more complex.