Re: PCI domains [Was: CVS commit: xsrc/external/mit/libpciaccess/dist/src]

[Michael <macallan%netbsd.org@localhost>]

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Hello,

On Jul 9, 2009, at 10:45 PM, Simon Burge wrote:

> 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.

If you want to map PCI IO space you do that once per host bridge, not  
once per bus which would be a waste. That's all the X code cares about.

have fun
Michael

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