On Fri, 2009-06-05 at 11:26 -0700, Greg KH wrote:
> Should the comedi layer just not be using PAGE_KERNEL_NOCACHE here? I
> can't believe that we need to do something like this in a driver. What
> should the proper fix for this be?
Actualy, I think powerpc -had- PAGE_KERNEL_NOCACHE and I removed it ...
Oh well... My understanding was that the exposed interface isn't that
but instead pgprot_noncached().
Nowadays we provide these on ppc:
#define pgprot_noncached(prot) (__pgprot((pgprot_val(prot) &
~_PAGE_CACHE_CTL) | \
_PAGE_NO_CACHE | _PAGE_GUARDED))
#define pgprot_noncached_wc(prot) (__pgprot((pgprot_val(prot) &
~_PAGE_CACHE_CTL) | \
_PAGE_NO_CACHE))
#define pgprot_cached(prot) (__pgprot((pgprot_val(prot) &
~_PAGE_CACHE_CTL) | \
_PAGE_COHERENT))
#define pgprot_cached_wthru(prot) (__pgprot((pgprot_val(prot) &
~_PAGE_CACHE_CTL) | \
_PAGE_COHERENT | _PAGE_WRITETHRU))
Now, of course, expect interesting problems if you use it in vmap, since
you are mapping struct pages, you are effectively mapping memory.
On some platforms, it's absolutely illegal to map memory non-cacheable while
this memory is mapped cacheable elsewhere and can be fatal. But the pages you
are mapping here, I suppose, are also part of the linear mapping which is ...
cacheable.
Why would you need that non-cacheable mapping in the first place ? If it's
for DMA, it's the wrong interface I believe....
Cheers,
Ben.
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