Re: FOR COMMENT: void __iomem * and similar casts are Bad News

[David Brownell <david-b@pacbell.net>]

On Wednesday 03 September 2008, Woodruff, Richard wrote:
> > > ... [ big/inexpensive fixed mappings can be virtuous ... ]
> >
> > ... which is exactly why some linux/arch/... code makes sure ioremap()
> > can return fixed mappings instead of always requiring dynamic ones.
> 
> That does sound like a nice consistent way to do it.  Which implementation
> of this would you recommend looking at?  Do any ARMs you know of do it today? 

I was just calling attention to the possibility.  ISTR seeing
that AVR32 does that, and I think some MIPS hardware has the
same kind of logic.  Not just those, either.

The ARM stuff seems to have changed since last I looked!

In arch/arm/include/asm/io.h there's an __arch_ioremap()
hook; it could be used instead of __arm_ioremap() ... and
it seems <mach/io.h> would define __arch_ioremap().

So at a first glance, OMAPs _could_ define that arch function
to look at the physical address to see if it's covered by a
fixed mapping, then reuse it ... else use __arm_ioremap().

According to Mr. Grep, there are at least 10 ARMs that work
like that in mainline.  Maybe Russell can recommend one of
them as a preferred model.

- Dave



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