Re: PCI domains

["M. Warner Losh" <imp%bsdimp.com@localhost>]

In message: <20090710024528.EC3695985C%thoreau.thistledown.com.au@localhost>
            Simon Burge <simonb%NetBSD.org@localhost> writes:
: Christoph Egger wrote:
: 
: > Michael Lorenz wrote:
: >
: > > +/*
: > > + * NetBSD's userland has a /dev/pci* entry for each bus but userland has 
no way
: > > + * to tell if a bus is a subordinate of another one or if it's on a 
different
: > > + * host bridge.
: > 
: > I have a patch which introduces support for PCI domains. It allows the
: > userland to distinguish between them by checking if the pci bus belongs
: > to the same PCI domain.
: 
: What exactly is a "PCI domain"?  A quick google seems to suggest that
: this is a Linux concept as opposed to a PCI concept.  In a previous
: life we used NetBSD on a number of different machines of various
: architectures that had multiple PCI host bridges, although admittedly we
: didn't need to know the topology of the PCI bus layout.

PCI domains, as implemented by Linux and FreeBSD are separate host
bridges.  Each bus complex behind the host bridge has independent
numbering.  Each of these bus complexes are in a different domain.

Not all systems with multiple host bridges have separate numbering
domains, but many do.

Warner