Hi Shirley,
I was reviewing write-combining for the PPC on kernel 2.6.30, and noticed the
following
in file arch/powerpc/include/asm/pgtable.h:
#define _PAGE_CACHE_CTL (_PAGE_COHERENT | _PAGE_GUARDED | _PAGE_NO_CACHE | \
_PAGE_WRITETHRU)
...
#define pgprot_noncached_wc(prot) (__pgprot((pgprot_val(prot) &
~_PAGE_CACHE_CTL) | \
_PAGE_NO_CACHE))
It seems to me that this gives the same result as the fix I put in OFED 1.5 for
the PPC:
(kernel_patches/fixes/mlx4_0010_add_wc.patch):
+pgprot_t pgprot_wc(pgprot_t _prot)
+{
+ return __pgprot((pgprot_val(_prot) | _PAGE_NO_CACHE) &
+ ~(pgprot_t)_PAGE_GUARDED);
+}
( That is, PAGE_NO_CACHE set, and _PAGE_GUARDED cleared).
Differences are that _PAGE_COHERENT and _PAGE_WRITETHRU are also cleared in
pgprot_noncached_wc()
and the patch I put in is only for PPC64, not all PPCs.
Questions:
1. Can I use the pgprot_noncached_wc() macro to implement write-combining on
all PPCs? (it is defined
thus in arch/powerpc/include/asm/pgtable.h for all PPC platforms)
2. Is there any reason that there is no define:
#define pgprot_writecombine pgprot_noncached_wc
in file arch/powerpc/include/asm/pgtable.h (so that the general
pgprot_writecombine() call can be used for PPCs as well).
-Jack
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