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SubjectRe: PCI-PCI bridges mess in 2.4.x


On Fri, 10 Nov 2000, Ivan Kokshaysky wrote:

> On Thu, Nov 09, 2000 at 09:37:41PM +0100, Gerard Roudier wrote:
> > Hmmm...
> > The PCI spec. says that Limit registers define the top addresses
> > _inclusive_.
>
> Correct.
>
> > The spec. does not seem to imagine that a Limit register lower than the
> > corresponding Base register will ever exist anywhere, in my opinion. :-)
>
> Not correct.
> Here's a quote from `PCI-to-PCI Bridge Architecture Specification rev 1.1':
> The Memory Limit register _must_ be programmed to a smaller value
> than the Memory Base if there are no memory-mapped I/O addresses on the
> secondary side of the bridge.

I only have spec 1.0 on paper. I should have checked 1.1. Anyway, it may
still exist bridges that have been designed prior to spec. 1.1.

> I/O is slightly different because it's optional for the bridge -
> but if it's implemented same rules apply.

Will also check the spec. on this point. :)

> > This let me think that trying to be clever here is probably a very bad
> > idea. What is so catastrophic of having 1 to 4 bytes of addresses and no
> > more being possibly in a forwardable range?
> >
> Huh. 1 to 4 bytes? 4K for I/O and 1M for memory.
> And it's not trying to be clever (anymore :-) - just strictly following
> the Specs.

I just missed the units, but absolute values weren't so wrong. :-)

> I understand your point very well, btw. I asked similar questions to myself
> until I've had the docs.

Ok. Thanks for the reply.

Gérard.

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