[RFC/PATCH] powerpc: Rewrite IO allocation & mapping on powerpc64

[Paul Mackerras]

Segher Boessenkool writes:

> This is wrong -- there are systems with ISA that
> also have PCI devices that require 16-bit legacy
> I/O windows (e.g., systems with the AMD8111 chip,
> like Maple).

If they are PCI devices and their drivers use a pci_dev's resources
to get to the device's I/O resources, then they are fine.

The only reason for reserving the low 64k is to cater for drivers that
use a hard-coded port number, e.g. video drivers using the VGA port
numbers.  We have been gradually getting rid of the hard coded port
numbers in drivers but I don't think they're all gone yet.

Paul.