Re: [PATCH v2 02/19] powerpc/8xx: Use SCRATCH0 and SCRATCH1 also for TLB handlers

From: Joakim Tjernlund
Date: Fri Aug 29 2014 - 11:06:13 EST


Christophe Leroy <christophe.leroy@xxxxxx> wrote on 2014/08/29 11:14:37:
>
> SCRATCH0 and SCRATCH1 are only used in Exceptions prologs where no other
> exception can happen. There is therefore no need to preserve them
accross
> TLB handlers, we can use them there as in other exceptions. One of the
> advantages is that they do not suffer CPU6 errata unlike M_TW register.

Really nice! Some comments below

>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
>
> ---
> arch/powerpc/kernel/head_8xx.S | 104
++++++++++++----------------------
> 1 files changed, 36 insertions(+), 68 deletions(-)
>
> diff --git a/arch/powerpc/kernel/head_8xx.S
b/arch/powerpc/kernel/head_8xx.S
> index 1329c5a..3af6db1 100644
> --- a/arch/powerpc/kernel/head_8xx.S
> +++ b/arch/powerpc/kernel/head_8xx.S
> @@ -104,12 +104,15 @@ turn_on_mmu:
> * task's thread_struct.
> */
> #define EXCEPTION_PROLOG \
> - mtspr SPRN_SPRG_SCRATCH0,r10; \
> - mtspr SPRN_SPRG_SCRATCH1,r11; \
> - mfcr r10; \
> + EXCEPTION_PROLOG_0; \
> EXCEPTION_PROLOG_1; \
> EXCEPTION_PROLOG_2
>
> +#define EXCEPTION_PROLOG_0 \
> + mtspr SPRN_SPRG_SCRATCH0,r10; \
> + mtspr SPRN_SPRG_SCRATCH1,r11; \
> + mfcr r10
> +
> #define EXCEPTION_PROLOG_1 \
> mfspr r11,SPRN_SRR1; /* check whether user or kernel */ \
> andi. r11,r11,MSR_PR; \
> @@ -145,6 +148,14 @@ turn_on_mmu:
> SAVE_2GPRS(7, r11)
>
> /*
> + * Exception exit code.
> + */
> +#define EXCEPTION_EPILOG_0 \
> + mtcr r10; \
> + mfspr r10,SPRN_SPRG_SCRATCH0; \
> + mfspr r11,SPRN_SPRG_SCRATCH1
> +
> +/*
> * Note: code which follows this uses cr0.eq (set if from kernel),
> * r11, r12 (SRR0), and r9 (SRR1).
> *
> @@ -293,16 +304,8 @@ InstructionTLBMiss:
> #ifdef CONFIG_8xx_CPU6
> stw r3, 8(r0)

Perhaps you can use SPRN_DAR to stash R3 now that it is free ?

Jocke
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