Re: Memory mapped IO vs Port IO

[jbarnes@sgi.com (Jesse Barnes)]

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