bus number into the bus argument. The bus number occupies the least
significant 8 bits. The PCI domain occupies the most significant 24
bits.
On the Altix 350, the PCI domain is a required parameter, but
changing the prototype of the pci_cfgreg*() functions to include a
separate domain argument has wide-spread consequences across the
supported architectures. We'd be changing a known interface.
Multiplexing is an acceptable kluge to give us what we need with
manageable impact. Note that the PCI bus number fits in 8 bits,
so the multiplexing of the domain is a backward compatible change.
cycles. This serves 2 purposes:
1. It prevents preemption and CPU migration while running SAL code.
2. It reduces the chance of stack overflows: we're supposed to enter
SAL with at least 16KB of either memory- or register stack space,
which we can't do without switching to a different stack.
