Re: [RFC] I/O Access Abstractions

Alan Cox
2001-07-02T22:16:10Z

> - Parsing of this cookie on each inx/outx access, which can
> take a bit of time (typically looking up the host bridge)

It depends on the implementation obviously, but its typically something like

take lock
writew(port&0xFFFF, port&0xFFFF0000);
writew(data, port&0xFFFF0000+1);
drop lock

Assuming you can drop the bridges on 64K boundaries in pci mem space, or
one extra deref and a register load if not.

Can you give me an idea of what sort of cookie decoding a PPC/PMac would need
and why - Im working off things like pa-risc so I dont have a full picture.