Re: [RFC/PATCH 1/3] powerpc: add ioremap_bat() function for setting up BAT translated IO regions.

["Grant Likely" <grant.likely@secretlab.ca>]

On Wed, Aug 6, 2008 at 8:07 AM, Kumar Gala <galak@kernel.crashing.org> wrote:
>
> On Aug 6, 2008, at 1:02 AM, Grant Likely wrote:
>
>> From: Grant Likely <grant.likely@secretlab.ca>
>>
>> ioremap_bat() is useful for things like mapping SoC internally memory
>> mapped
>> register and early text because it allows mappings to devices to be setup
>> early in the boot process where they are needed, and the mappings persist
>> after the MMU is configured.
>>
>> Without ioremap_bat(), setting up the MMU would cause the early text
>> mappings to get lost and mostly likely result in a kernel panic on the
>> next
>> attempt at output.
>>
>> Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
>> ---
>
> why can't we just do this in ioremap itself?

I suppose we could; but the usecase is somewhat different and I wanted
to keep it simple.  Using a separate API also helps reenforce that the
caller really needs to know what they are doing because BATs are a
limited resource.

g.

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