Re: [PATCH v3 2/2] powerpc/8xx: use _PAGE_RO instead of _PAGE_RW

Joakim Tjernlund
2015-01-05T18:21:02Z

On Mon, 2014-12-22 at 11:14 +0100, Christophe Leroy wrote:
> On powerpc 8xx, in TLB entries, 0x400 bit is set to 1 for read-only pages
> and is set to 0 for RW pages. So we should use _PAGE_RO instead of _PAGE_=
RW
>=20
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Hi Christophe, been meaning to look over all you recent 8xx MMU/TLB patches
but got so little time :(

This is very cool (not sure if there will be a performance gain) but ..
>=20
>=20
>=20
> diff --git a/arch/powerpc/include/asm/pgtable-ppc32.h b/arch/powerpc/incl=
ude/asm/pgtable-ppc32.h
> index caf094a..b4e0c3b 100644
> --- a/arch/powerpc/include/asm/pgtable-ppc32.h
> +++ b/arch/powerpc/include/asm/pgtable-ppc32.h
> @@ -178,9 +178,10 @@ static inline unsigned long pte_update(pte_t *p,
> andc %1,%0,%5\n\
> or %1,%1,%6\n\
> /* 0x200 =3D=3D Extended encoding, bit 22 */ \
> - /* Bit 22 has to be 1 if neither _PAGE_USER nor _PAGE_RW are set =
*/ \
> + /* Bit 22 has to be 1 when _PAGE_USER is unset and _PAGE_RO is se=
t */ \
> rlwimi %1,%1,32-2,0x200\n /* get _PAGE_USER */ \
> - rlwinm %3,%1,32-1,0x200\n /* get _PAGE_RW */ \
> + rlwinm %3,%1,32-1,0x200\n /* get _PAGE_RO */ \
> + xori %3,%3,0x200\n \
> or %1,%3,%1\n\
> xori %1,%1,0x200\n"
> " stwcx. %1,0,%4\n\

... here I expected to loose the existing xori insn instead of adding one?

Jocke=