Minor cleanups in pci_irq.c

[neel]

Summary

• Set 'pirq_cold' to '0' when the first PIRQ allocation happens.
• Make assertions stronger.

Test Plan

Booted an i386 guest with hint.apic.0.disabled=1 and verified legacy interrupts
with attimer, uart, virtio-block and virtio-net.

[jhb]

I think this is fine. In theory pirq_alloc_pin() should fail and return a pin of -1 if it fails to route an IRQ (if the loop around irq_counts failed to find a non-disabled IRQ). In that case you would want pirq_pin() to return 255 as that is how BIOS's mark unrouted interrupts. (It would also DTRT if the caller hadn't yet routed the interrupt.) In practice there should always be at least one free IRQ (esp if ACPI is enabled as then the SCI IRQ is available).

usr.sbin/bhyve/pci_irq.c

200

Doh!