Resending, adding Hoang-Nam Nguyen and Christoph Raisch of IBM.
Please see the questions below. Also, who is the person at IBM who does Linux
kernel devleopment for the PPC?
Thanks!
-Jack
On Sunday 28 June 2009 12:21, Jack Morgenstein wrote:
> 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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