On Fri, Nov 30, 2007 at 04:14:55PM -0600, Kumar Gala wrote:
> Ben and I are talking about using fixmap on ppc for similar applications to
> it use on x86. However in poking around other arch's (sparc, mips) they
> appear to have some support but not as complete as x86.
>
> For example both SPARC & MIPS reference __set_fixmap() in asm/fixmap.h but
> I can't find an implementation on either.
>
> So I was wondering if there was some reason fixmap isn't as well supported
> or if its just used for a specific function on those SPARC, MIPS, etc. and
> they dont need as much functionality out of it as x86 does.
MIPS uses fixmap for two purposes:
o In some cases it is possibly to avoid or optimize a cacheflush by creating
a temporary mapping. The mechanism works very similar to what x86 and
MIPS use for atomic kmaps.
o Highmem.
Both manipulate pagetables directly or even insert entries directly into
the TLB without pagetables as intermediate stage so __set_fixmap is indeed
unused.
Ralf
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