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

[Kumar Gala]

On Aug 6, 2008, at 4:54 PM, Grant Likely wrote:

> On Wed, Aug 6, 2008 at 8:07 AM, Kumar Gala  
> <galak at kernel.crashing.org> wrote:
>>
>> On Aug 6, 2008, at 1:02 AM, Grant Likely wrote:
>>
>>> From: Grant Likely <grant.likely at 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 at 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.

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.

- k