Re: [PATCH 2.6.19 2/4] ehca: hcp_phyp.c: correct page mapping in 64k page mode

[Paul Mackerras <paulus@samba.org>]

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.