On Thu, May 10, 2001 at 11:11:53AM -0700, Jun Sun wrote:
> I would not normally assign IO space above 0xffff either. But recently I
> found multiple PCI buses, especially dual PCI buses, are getting popular, as
> examplified by two Gallelio chips and the new NEC Vrc5477 chips.
>
> Since all drivers share the same mips_io_port_base, - even though the devices
> may be on different PCI buses - we need to assign the PCI IO windows
> contiguously so that drivers can share the same base address. In most such
> setups, you will get more than 0xffff IO ranges.
After some discussion with some of the Linux PCI guys I think we should try
to avoid extend the per-bus I/O address space beyond 64k ports. This is not
a very strong ``should avoid'', though. The primary concern is a number of
broken peripheral chips which apparently are floating around out there in
good numbers.
Another reason to not extend the PCI-bus address range to 4g ports is the
size of the available physical address space in the main processor's
address space itself. Limited by the 32-bit address space we can only
address a limited number via in/out anyway, so we better shouldn't fake
what we ain't got (cited freely after Seymoure Cray), so 4g ports is silly
anyway.
Ralf
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