Subject: Re: [PATCH 5/6] powerpc: Macros for saving/restore PPR

From: Michael Neuling <[email-masked]>
Date: Fri, 23 Nov 2012 14:39:57 +1100

Haren Myneni <[email-masked]> wrote:

> [PATCH 5/6] powerpc: Macros for saving/restore PPR
> 
> Several macros are defined for saving and restore user defined PPR value.
> 
> Signed-off-by: Haren Myneni <[email-masked]>
> ---
>  arch/powerpc/include/asm/exception-64s.h |   29 +++++++++++++++++++++++++++++
>  arch/powerpc/include/asm/ppc_asm.h       |   25 +++++++++++++++++++++++++
>  arch/powerpc/include/asm/reg.h           |    1 +
>  3 files changed, 55 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
> index bfd3f1f..880ef7d 100644
> --- a/arch/powerpc/include/asm/exception-64s.h
> +++ b/arch/powerpc/include/asm/exception-64s.h
> @@ -62,6 +62,35 @@
>  #define EXC_HV	H
>  #define EXC_STD
>  
> +/*
> + * PPR save/restore macros used in exceptions_64s.S  
> + * Used for P7 or later processors
> + */
> +#define SAVE_PPR(area, ra, rb)						\
> +BEGIN_FTR_SECTION_NESTED(940)						\
> +	ld	ra,PACACURRENT(r13);					\
> +	ld	rb,area+EX_PPR(r13);	/* Read PPR from paca */	\
> +	std	rb,TASKTHREADPPR(ra);					\
> +END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,940)
> +
> +#define RESTORE_PPR_PACA(area, ra)					\
> +BEGIN_FTR_SECTION_NESTED(941)						\
> +	ld	ra,area+EX_PPR(r13);					\
> +	mtspr	SPRN_PPR,ra;						\
> +END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,941)
> +

Can you add some documentation here on why we should use the different
versions.

I'm trying to read the next patch and it's not clear to my why some have
HMT_MEDIUM_NO_PPR and other times HMT_MEDIUM and others
HTM_MEDIUM_HAS_PPR.

Looks like HTM_MEDIUM_NO_PPR sets the priority to medium on systems
where we can't save/restore the PPR, hence it can be called earlier in
the exception handler before we have free GPRs.  HTM_MEDIUM_HAS_PPR
saves the priority on systems where it can, and then sets the priority
to medium.

Maybe we should change the names 
  HTM_MEDIUM_NO_PPR  => HTM_MEDIUM_PPR_DISCARD   and
  HTM_MEDIUM_HAS_PPR => HTM_MEDIUM_PPR_SAVE
But now I'm heading into bike shedding territory... plus I think I
suggested the names you have currently, so I'm feeling a bit dumb now
:-)

Mikey

> +#define HMT_MEDIUM_NO_PPR						\
> +BEGIN_FTR_SECTION_NESTED(942)						\
> +	HMT_MEDIUM;							\
> +END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,0,942)  /*non P7*/		
> +
> +#define HMT_MEDIUM_HAS_PPR(area, ra)					\
> +BEGIN_FTR_SECTION_NESTED(943)						\
> +	mfspr	ra,SPRN_PPR;						\
> +	std	ra,area+EX_PPR(r13);					\
> +	HMT_MEDIUM;							\
> +END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,943) 
> +
>  #define __EXCEPTION_PROLOG_1(area, extra, vec)				\
>  	GET_PACA(r13);							\
>  	std	r9,area+EX_R9(r13);	/* save r9 - r12 */		\

> diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
> index 376e36d..52649cc 100644
> --- a/arch/powerpc/include/asm/ppc_asm.h
> +++ b/arch/powerpc/include/asm/ppc_asm.h
> @@ -389,6 +389,31 @@ END_FTR_SECTION_IFCLR(CPU_FTR_601)
>  	FTR_SECTION_ELSE_NESTED(848);	\
>  	mtocrf (FXM), RS;		\
>  	ALT_FTR_SECTION_END_NESTED_IFCLR(CPU_FTR_NOEXECUTE, 848)
> +
> +/*
> + * PPR restore macros used in entry_64.S
> + * Used for P7 or later processors
> + */
> +#define HMT_MEDIUM_LOW_HAS_PPR						\
> +BEGIN_FTR_SECTION_NESTED(944)						\
> +	HMT_MEDIUM_LOW;							\
> +END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,944)
> +
> +#define SET_DEFAULT_THREAD_PPR(ra, rb)					\
> +BEGIN_FTR_SECTION_NESTED(945)						\
> +	lis	ra,0xc;		/* default ppr=3 */			\
> +	ld	rb,PACACURRENT(r13);					\
> +	sldi	ra,ra,32;	/* 11- 13 bits are used for ppr */	\
> +	std	ra,TASKTHREADPPR(rb);					\
> +END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,945)
> +
> +#define RESTORE_PPR(ra, rb)						\
> +BEGIN_FTR_SECTION_NESTED(946)						\
> +	ld	ra,PACACURRENT(r13);					\
> +	ld	rb,TASKTHREADPPR(ra);					\
> +	mtspr	SPRN_PPR,rb;	/* Restore PPR */			\
> +END_FTR_SECTION_NESTED(CPU_FTR_HAS_PPR,CPU_FTR_HAS_PPR,946)
> +
>  #endif
>  
>  /*
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index d24c141..1723be3 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -287,6 +287,7 @@
>  #define SPRN_DBAT6U	0x23C	/* Data BAT 6 Upper Register */
>  #define SPRN_DBAT7L	0x23F	/* Data BAT 7 Lower Register */
>  #define SPRN_DBAT7U	0x23E	/* Data BAT 7 Upper Register */
> +#define SPRN_PPR	0x380	/* SMT Thread status Register */
>  
>  #define SPRN_DEC	0x016		/* Decrement Register */
>  #define SPRN_DER	0x095		/* Debug Enable Regsiter */
> -- 
> 1.7.1
> 
> 
> 
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