Christoph Raisch writes:
> ioremap maps 4k pages on 4k kernels and on 64k pages on 64k kernels. So far
> the theory.
>
> This is true for memory.
And for I/O. :) ioremap updates the (Linux) page tables that map the
vmalloc/ioremap area, and that is at page granularity. So there is in
fact no difference in the end result in the page tables whether you
ask to map a small amount inside a page, or the whole page.
> On POWER the ebus memory is mapped by H_ENTER.
> The hypervisor checks for 4k page size on H_ENTER, reason see above.
The next part of the story is that the low-level MMU code on System-P
(pSeries) machines only does the H_ENTER when you access an I/O
mapping. It does H_ENTER for 4k pages for non-cacheable mappings,
and it only does the H_ENTER for the 4k subpages of a 64k page that
the kernel actually accesses.
So Roland is correct in his comment about how ioremap is called.
Regards,
Paul.
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