Okay, I think I've figured out how this is supposed to work. With these
two patches to SeaBIOS and the patch to qemu, I can run:
qemu -net nic,model=rtl8139 -net nic,model=virtio -net nic,model=e1000
-boot menu=on
And all three option roms load. I can also select which NIC I want to
boot from using the F12 menu. This works by not actually loading the
option roms in the 1M space, but instead making them mappable through
the PCI devices. With PMM and DDIM, the result is that we only have to
copy in 2K for each option rom which means we can support up to 48
unique option roms. That should be plenty for now.
These patches are very rough but I'll clean them up tomorrow. I'm not
sure the best way to integrate with the rom infrastructure since we no
longer have a physical address to map to. Any suggestions Gerd?