Re: Memory mapped IO vs Port IO

Jesse Barnes
2003-09-11T16:14:57Z

On Thu, Sep 11, 2003 at 05:01:16PM +0100, Matthew Wilcox wrote:
> config MMIO
> bool "Prefer Memory-mapped I/O accesses over Port I/O"
> help
> Many devices are accessible via both memory mapped I/O and
> port I/O. Say Y here to access them via the slightly faster
> memory mapped I/O method. If you experience problems, you may
> wish to say N here.
>
> If that's not acceptable, can I suggest that we at least ask a standard
> question?
>
> config WWWW_MMIO
> bool "Use Memory mapped I/O in preference to Port I/O"
> depends on WWWW
> help
> This device's registers can be accessed by either memory
> mapped I/O or port I/O. Memory mapped I/O is faster, so you
> are advised to say Y here.
>
> (yes, we could wordsmith these questions into the ground; the key point
> of this mail is whether we ask one question at the start of configuration
> or whether we ask one question per device.)

I like this idea, esp. as a global option. It would help e.g. visws
which can't reliably do MMIO. Most platforms could default MMIO to y
also, to make things easier.

Jesse