Chris,
I noticed the following comment in pgtable.h:
* - CACHE COHERENT bit (M) has no effect on PPC440 core, because it
* doesn't support SMP. So we can use this as software bit, like
* DIRTY.
And _PAGE_COHERENT is not defined for the 44x (giving a compile error
when I add it the _PAGE_BASE line as you suggested). This would confirm
that the M bit is meaningless for the PPC440
Regards,
Adam
On Thu, 2009-09-03 at 09:05 +0100, Chris Pringle wrote:
> Hi Adam,
>
> If you have a look in include/asm-ppc/pgtable.h for the following section:
> #ifdef CONFIG_44x
> #define _PAGE_BASE (_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_GUARDED)
> #else
> #define _PAGE_BASE (_PAGE_PRESENT | _PAGE_ACCESSED)
> #endif
>
> Try adding _PAGE_COHERENT to the appropriate line above and see if that
> fixes your issue - this causes the 'M' bit to be set on the page which
> sure enforce cache coherency. If it doesn't, you'll need to check the
> 'M' bit isn't being masked out in head_44x.S (it was originally masked
> out on arch/powerpc, but was fixed in later kernels when the cache
> coherency issues with non-SMP systems were resolved).
>
> The patch I had fixed two problems on 2.6.26 for 'powerpc':
> 1) It stopped the 'M' bit being masked out (head_32.S)
> 2) It set the cache coherency ('M' bit) flag on each page table entry
> (pgtable-ppc32.h)
>
> Hope this helps!
>
> Cheers,
> Chris
>
> Adam Zilkie wrote:
> > Hi Chris,
> >
> > I am having a problem similar to what you described in this discussion.
> > We are using the ppc arch with 2.6.24 with CONFIG_SEQUOIA with compiles
> > arch/ppc/kernel/head_44x.c (quite different
> > from /arch/powerpc/kernel/head_32.S). I would like to apply your
> > backporting patch to this architecture. Any help would be appreciated.
> >
> > Regards,
> > Adam
> >
> >
>
>
--
Adam Zilkie
Software Designer,
International Datacasting Corp.
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