Re: Memory mapped IO vs Port IO

[Andi Kleen <ak@suse.de>]

Matthew Wilcox <willy@debian.org> writes:

> There's a lot of drivers in the tree that allow you to access the device
> either via IO port space or IO mem space.  Here's some examples:

My gut feeling is to just fix the drivers to make this runtime switchable
and get rid of the compile time options.

This would help distributions (who normally want to build conservative
by default, but still allow the users easy tuning without recompilation) 
For that it would be nice if a standard module parameter or maybe 
sysfs option existed.

The overhead of checking for PIO vs mmio at runtime in the drivers
should be completely in the noise on any non ancient CPU (both MMIO
and PIO typically take hundreds or thousands of CPU cycles for the bus
access, having an dynamic function call or an if before that is makes
no difference at all)

-Andi