On Mon, Jul 23, 2012 at 01:51:49PM +0530, Aneesh Kumar K.V wrote:
> Paul Mackerras <pau...@samba.org> writes:
>
> > On Mon, Jul 09, 2012 at 06:43:39PM +0530, Aneesh Kumar K.V wrote:
> >> From: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
> >>
> >> Increase the number of valid VSID bits in slbmte instruction.
> >> We will use the new bits when we increase valid VSID bits.
> >>
> >> Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com>
> >> ---
> >> arch/powerpc/mm/slb_low.S | 4 ++--
> >> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/powerpc/mm/slb_low.S b/arch/powerpc/mm/slb_low.S
> >> index c355af6..c1fc81c 100644
> >> --- a/arch/powerpc/mm/slb_low.S
> >> +++ b/arch/powerpc/mm/slb_low.S
> >> @@ -226,7 +226,7 @@ _GLOBAL(slb_allocate_user)
> >> */
> >> slb_finish_load:
> >> ASM_VSID_SCRAMBLE(r10,r9,256M)
> >> - rldimi r11,r10,SLB_VSID_SHIFT,16 /* combine VSID and flags */
> >> + rldimi r11,r10,SLB_VSID_SHIFT,2 /* combine VSID and flags */
> >
> > You can't do that without either changing ASM_VSID_SCRAMBLE or masking
> > the VSID it generates to 36 bits, since the logic in ASM_VSID_SCRAMBLE
> > can leave non-zero bits in the high 28 bits of the result. Similarly
> > for the 1T case.
> >
>
> How about change ASM_VSID_SCRAMBLE to clear the high bits ? That would
> also make it close to vsid_scramble()
One more instruction in a hot path - I'd rather not. How about
changing the rldimi instruction to:
rldimi r11,r10,SLB_VSID_SHIFT,(64-SLB_VSID_SHIFT-VSID_BITS_256M)
and similarly for the 1T case. That will give the proper masking
when you change VSID_BITS_256M.
Paul.
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