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SubjectRe: PCI-PCI bridges mess in 2.4.x
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_.


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

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

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