"Maciej W. Rozycki" wrote:
> On Wed, 9 May 2001, Jun Sun wrote:
> > The PCI IO space essentially extends the ISA bus, which effectively removes
> > the 0xffff limits.
> Note that while there is usually no problem with using addresses beyond
> 64kB in the PCI I/O space, certain PCI-to-PCI bridges may not pass such
> accesses across. So it's best to avoid assigning and using them. That's
> why Linux remaps "high" I/O space resources on Alpha, which get set up for
> some systems by the SRM console (firmware), e.g. in the system I was using
> a few years ago, SRM used to assign addresses around 0x11000 and 0x12000
> for the onboard network and SCSI devices, IIRC.
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.