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SubjectRe: powerpc/e200: Skip tlb1 entries used for kernel mapping
On Tue, Jul 24, 2018 at 11:29:45AM +0530, Bharat Bhushan wrote:
> E200 have TLB1 only and it does not have TLB0.
> So TLB1 are used for mapping kernel and user-space both.
> TLB miss handler for E200 does not consider skipping TLBs
> used for kernel mapping. This patch ensures that we skip
> tlb1 entries used for kernel mapping (tlbcam_index).

How much more is needed to get e200 working? What was this tested on?

> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@nxp.com>
> ---
> arch/powerpc/kernel/head_fsl_booke.S | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/head_fsl_booke.S b/arch/powerpc/kernel/head_fsl_booke.S
> index bf4c602..951fb96 100644
> --- a/arch/powerpc/kernel/head_fsl_booke.S
> +++ b/arch/powerpc/kernel/head_fsl_booke.S
> @@ -801,12 +801,28 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_BIG_PHYS)
> /* Round robin TLB1 entries assignment */
> mfspr r12, SPRN_MAS0
>
> + /* Get first free tlbcam entry */
> + lis r11, tlbcam_index@ha
> + lwz r11, tlbcam_index@l(r11)

The existing handler already loads tlbcam_index and uses that when
wrapping. What specifically is causing that to not work (perhaps it's
just a matter of initializing NV when tlbcam_index changes?), and why
does this patch leave that code in place?

> +
> + /* Extract MAS0(NV) */
> + andi. r13, r12, 0xfff
> + cmpw 0, r13, r11
> + blt 0, 5f
> + b 6f
> +5:

Why these two instructions instead of "bge 6f"? If it's for branch
prediction, does e200 pay attention to static hints? If it doesn't,
you could move the wrap code out-of-line.

> + /* When NV is less than first free tlbcam entry, use first free
> + * tlbcam entry for ESEL and set NV */
> + rlwimi r12, r11, 16, 4, 15
> + addi r11, r11, 1
> + rlwimi r12, r11, 0, 20, 31
> + b 7f

The 4-argument form of rlwimi is easier to read.

BTW, The TLB miss handler would be simpler/faster if you reserve the
upper entries rather than the lower entries. Then you would just have
one value to check (instead of using TLB1CFG[NENTRY]) to see if you wrap
back to zero.

-Scott

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