Subject: Re: pci in arch/powerpc vs arch/ppc

From: Segher Boessenkool <[email-masked]>
Date: Thu, 9 Aug 2007 17:56:05 +0200

> It means the bus on which legacy I/O ports can be found.  It's a fairly
> broken concept; each host bridge should really be treated as a
> completely separate entity, and if something like a VGA card has legacy
> I/O ports that need to be used, they should be looked for on the same
> PCI bus as the card itself.  Legacy ISA ports should be discovered
> through the device tree (or platform devices, or whatever) that
> explicitly state which PCI-to-ISA bridge they're under.

Currently, Linux does not allow multiple PCI domains to use
overlapping legacy I/O ranges.  Yeah it's a pain.

> Yes, apparently -- according to a recent thread here, recent versions 
> of
> the PCI spec removed the wording that prohibited a zero BAR (is there
> then no way to disable a BAR?).

I couldn't find that prohibition even in ancient versions of
the PCI specification, for what it's worth.  Maybe I'm just
blind.

> Still, it'd be better to avoid it.

Yeah, many drivers go bonkers otherwise.  Some devices might
misbehave, too.

Segher