getpir just reads the $PIR table in memory as set by the bios. I am wondering if the bios on your board is one of the defective BIOSes that doesn't have the $PIR entries for all devices. There are many of these. If so, you are going to have to hand-edit that .c file and add the entries yourself. in the case of defective $PIR tables what the BIOS writers do is just set the IRQ line by hand in the pci device.
Sometimes you can just trust the value from stock PIRQ table. Some boards come with faulty table.
-Andrew