Re: PCI domains

["Christoph Egger" <Christoph_Egger%gmx.de@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.

PCI domains are part of the PCI host bridge specification.
It is a 16bit-wide number.

Christoph