RFC: Deprecating io_block_mapping

Kumar Gala kumar.gala at freescale.com
Wed May 25 16:08:06 EST 2005

>> Somewhere, at some point, prior to VM setup, we need to forcibly map
>> virtual to physical addresses.  These are going to be "hard coded"
>> mappings, that's exactly how ioremap_bot is set.  This is why
>> io_block_mapping was created in the first place.  Somehow you have
>> to specify this mapping before you have a VM allocator to give it to
>> you. :-)
> No, you just need to have ioremap_bot (which is in fact "top" not
> "bottom", bad naming) initialized to something sane. This is currently
> done in MMU_init() but could probably be initialized statically 
> instead.
> I do just that on ppc64 and thus can ioremap at any time without 
> needing
> to allocate vmalloc space. The vmalloc space is automatically "cap'd" 
> by
> ioremap_bot anyway.

Can one of you explain why this is necessary.  I believe it I just dont 
understand.  I think this is one of the abuses of io_block_mapping().  
People, myself included, realize some of the caveats implied by calling 

- kumar

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