Patches added to powerpc.git master and powerpc-next branches

[Kumar Gala]

On Apr 21, 2008, at 7:15 PM, Paul Mackerras wrote:
> Kumar Gala writes:
>
>>> Once again I want to go through it carefully and understand how it  
>>> all
>>> works, and in particular understand things like the way it ensures
>>> that the base address for the kmap region is aligned to a 4M  
>>> boundary
>>> so all the kmap ptes are in a single page (assuming it does :).
>>
>> I'm not clear on why this is needed.  I can see value in having the
>> PGD entry in place but the pte PAs would be changing all the time  
>> so I
>> don't see what benefit there is in keeping them in one page.
>
> Have a look at map_new_virtual in mm/highmem.c.  In particular:
>
>        set_pte_at(&init_mm, vaddr,
>                   &(pkmap_page_table[last_pkmap_nr]), mk_pte(page,  
> kmap_prot));
>
> assumes that the ptes that kmap uses are in a contiguous array whose
> base is pkmap_page_table.
>
>> For normal kmap ptes we cover things in one PGD via:
>>
>> #define PKMAP_BASE      ((FIXADDR_BOOT_START -  
>> PAGE_SIZE*(LAST_PKMAP +
>> 1)) & PMD_MASK)
>
> OK, that probably does the trick ... <checks> ... yes it does.
>
> We seem to have a distinction without a difference between
> FIXADDR_START and FIXADDR_BOOT_START, and similarly between
> __FIXADDR_SIZE and __FIXADDR_BOOT_SIZE.  Is there any actual
> difference and if not why do we have two names for the same thing?
>
>
> Also, we seem to have an unnecessary distinction (and unnecessary
> casting) between __FIXADDR_TOP and FIXADDR_TOP.

its left over from the x86 port.  I'll get rid of __FIXADDR_BOOT_SIZE,  
FIXADDR_BOOT_START, and __FIXADDR_TOP.

If we want the early ioremap support in the future we can add back  
__FIXADDR_BOOT_SIZE and FIXADDR_BOOT_START.

- k