[coreboot] Interrupt confusion CK804 Tyan s2895

[Myles Watson]

I have a Tyan s2895 board and I'm using a PCIe GeForce 6600 Video
adapter.  With the factory BIOS, lspci shows the interrupt routed to
IRQ 5, and it works fine.

With Coreboot, lscpi shows the interrupt routed to IRQ 18 (value from
mptable), and it finally loads X after a few tries in low resolution
mode.

With Coreboot and ACPI the interrupt gets routed to IRQ 0, even though
I put 18 in the _PRT table.  X loads more quickly, but there are
obvious problems with text highlighting.

In none of the three cases can I find the IRQ listed  in
/proc/interrupts.  I would have expected to see it there.

I don't see anything in dmesg that seems to be related to IRQ 18.

Can anyone suggest the next step?

Thanks,
Myles