Add pci_find_next_cap, pci_find_next_extcap, and pci_find_next_htcap

[bryanv]

Summary

This is used in VirtIO v1 to iterate over all the VENDOR capabilities.

Test Plan

VirtIO PCI v1 is working with pci_find_next_cap. I don't have a way to test the others.

[jhb]

Looks fine overall, just some suggestions / nits.

share/man/man9/pci.9

355

Nit, drop 'the' here and in the other two places.

sys/dev/pci/pci.c

1420

Perhaps add a KASSERT() that that 'pci_read_config(child, start + PCICAP_ID, 1) == PCIY_HT'? More paranoid would be to add a further assertion that the nested capbility in PCIR_HT_COMMAND from 'start' matches 'capability'.

1427

Do you think this should use 'pci_find_next_cap(PCIY_HT)'?

1517

I would add 'KASSERT(pci_read_config(child, start + PCICAP_ID, 1) == capability)' at the start.

1585

I would change this to:

ecap = pci_read_config(child, start, 4);
KASSERT(PCI_EXTCAP_ID(ecap) == capability, ...);
ptr = PCI_EXTCAP_NEXTPTR(ecap);

[bryanv]

sys/dev/pci/pci.c

1427

Yes. I'll change pci_find_htcap_method too.