a60f2abe1f
three registers. Let us think of the kernel operating the registers
in two steps:
1) Select: enable configuration cycles and select a range of
configuration-space addresses.
2) Access: read or write a word in PCI configuration space.
To make the steps more explicit, extract some helper subroutines
from pci_conf_read(9) and pci_conf_write(9):
pci_conf_selector(tag, reg): from a pcitag_t and a register offset,
create a word that enables configuration cycles and selects a
configuration address range.
pci_conf_select(w): for `w' a word created by pci_conf_selector(),
enable configuration cycles and select the address range indicated
by `w'.
pci_conf_select(0): disable configuration cycles.
pci_conf_port(tag, reg): map a pcitag_t and a register offset to an I/O
port where the configuration access should occur.
While I'm in here, change the panic(9) calls to panic("%s: ...",
__func__) instead of hard-coding a subroutine name.