David Gibson <dwg@xxxxxxxxxxx> writes:
> On Thu, Apr 11, 2013 at 10:50:12AM +0530, Aneesh Kumar K.V wrote:
>> David Gibson <dwg@xxxxxxxxxxx> writes:
>>
>> > On Thu, Apr 04, 2013 at 11:27:51AM +0530, Aneesh Kumar K.V wrote:
>> >> From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>> >>
>> >> This make sure we handle multiple page size segment correctly.
>> >
>> > This needs a much more detailed message. In what way was the existing
>> > code not matching the ISA documentation? What consequences did that
>> > have?
>>
>> Mostly to make sure we use the right penc values in tlbie. I did test
>> these changes on PowerNV.
>
> A vague description like this is not adequate. Your commit message
> needs to explain what was wrong with the existing behaviour.
>
>> >> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>> >> ---
>> >> arch/powerpc/mm/hash_native_64.c | 30 ++++++++++++++++++++++++++++--
>> >> 1 file changed, 28 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/arch/powerpc/mm/hash_native_64.c b/arch/powerpc/mm/hash_native_64.c
>> >> index b461b2d..ac84fa6 100644
>> >> --- a/arch/powerpc/mm/hash_native_64.c
>> >> +++ b/arch/powerpc/mm/hash_native_64.c
>> >> @@ -61,7 +61,10 @@ static inline void __tlbie(unsigned long vpn, int psize, int apsize, int ssize)
>> >>
>> >> switch (psize) {
>> >> case MMU_PAGE_4K:
>> >> + /* clear out bits after (52) [0....52.....63] */
>> >> + va &= ~((1ul << (64 - 52)) - 1);
>> >> va |= ssize << 8;
>> >> + va |= mmu_psize_defs[apsize].sllp << 6;
>> >
>> > sllp is the per-segment encoding, so it sure must be looked up via
>> > psize, not apsize.
>>
>> as per ISA doc, for base page size 4K, RB[56:58] must be set to
>> SLB[L|LP] encoded for the page size corresponding to the actual page
>> size specified by the PTE that was used to create the the TLB entry to
>> be invalidated.
>
> Ok, I see. Wow, our architecture is even more convoluted than I
> thought. This could really do with a comment, because this is a very
> surprising aspect of the architecture.
>
>> >
>> >> asm volatile(ASM_FTR_IFCLR("tlbie %0,0", PPC_TLBIE(%1,%0), %2)
>> >> : : "r" (va), "r"(0), "i" (CPU_FTR_ARCH_206)
>> >> : "memory");
>> >> @@ -69,9 +72,19 @@ static inline void __tlbie(unsigned long vpn, int psize, int apsize, int ssize)
>> >> default:
>> >> /* We need 14 to 14 + i bits of va */
>> >> penc = mmu_psize_defs[psize].penc[apsize];
>> >> - va &= ~((1ul << mmu_psize_defs[psize].shift) - 1);
>> >> + va &= ~((1ul << mmu_psize_defs[apsize].shift) - 1);
>> >> va |= penc << 12;
>> >> va |= ssize << 8;
>> >> + /* Add AVAL part */
>> >> + if (psize != apsize) {
>> >> + /*
>> >> + * MPSS, 64K base page size and 16MB parge page size
>> >> + * We don't need all the bits, but this seems to work.
>> >> + * vpn cover upto 65 bits of va. (0...65) and we need
>> >> + * 58..64 bits of va.
>> >
>> > "seems to work" is not a comment I like to see in core MMU code...
>> >
>>
>> As per ISA spec, the "other bits" in RB[56:62] must be ignored by the
>> processor. Hence I didn't bother to do zero it out. Since we only
>> support one MPSS combination, we could easily zero out using 0xf0.
>
> Then update the comment to clearly explain why what you're doing is
> correct, not just say it "seems to work".
Will do.
-aneesh
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