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Date: Wed, 6 Aug 2008 17:11:27 -0600
From: "Grant Likely" <grant.likely@secretlab.ca>
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Subject: Re: [RFC/PATCH 1/3] powerpc: add ioremap_bat() function for setting
	up BAT translated IO regions.
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On Wed, Aug 6, 2008 at 4:28 PM, Benjamin Herrenschmidt
<benh@kernel.crashing.org> wrote:
>
>> there is a bunch of error checking and difference in semantics that
>> you need to fix.  I think introduce a new API for this is silly,
>> especially since we expect there to only be one actual invocation of
>> the API for serial console access.
>
> Not necessarily....
>
> There's another aspect to BAT mappings here. First, they should be
> permanent (ie, not unmappable). That way, we have ioremap just use
> an existing BAT mapping when asked for a device that is covered
> by a BAT. This allows to have platform code do something like setup
> a BAT over a bunch of SOC registers or over a device, to automagically
> get drivers doing ioremap to that area benefit from it.

Actually, that is exactly what I am in the process of doing right now
for all the 5200 platforms.  It is a performance win with no apparent
downside.

Next I want to investigate if it makes sense to do it for PCI IO regions.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.