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

[Grant Likely]

On Wed, Aug 6, 2008 at 4:11 PM, Kumar Gala <galak at kernel.crashing.org> wrote:
>
> 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.

details please?  I agree that it can be tightened up in some areas,
but I'd like to know if you've seen something I haven't.

>  I think introduce a new API for this is silly,

I don't think so.  I actually prefer it being an different API.  It
forces the caller to understand what the function does.  It forces the
programmer to think and to understand the effect of mapping large io
blocks.

> especially since we
> expect there to only be one actual invocation of the API for serial console
> access.

Actually, this is not only for early serial.  Early serial just
happens to be the first user.

g.

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