linux-kernel - Re: [PATCH] powerpc/8xx: fix single

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Date:	Thu, 18 Aug 2016 11:58:07 +0200
From:	Gabriel Paubert <paubert@...m.es>
To:	Christophe Leroy <christophe.leroy@....fr>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Scott Wood <oss@...error.net>, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/8xx: fix single_step debug

On Thu, Aug 18, 2016 at 11:44:20AM +0200, Christophe Leroy wrote:
> SPRN_ICR must be read for clearing the internal freeze signal which
> is asserted by the single step exception, otherwise the timebase and
> decrementer remain freezed

Minor nit: s/freezed/frozen/

If the timebase and decrementer are frozen even for a few cycles, this
probably upsets timekeeping. I consider this a completely stupid design
decision, and maybe I'm not alone.

    Gabriel

> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/include/asm/reg_8xx.h | 1 +
>  arch/powerpc/kernel/traps.c        | 8 ++++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/reg_8xx.h b/arch/powerpc/include/asm/reg_8xx.h
> index feaf641..6dae71f 100644
> --- a/arch/powerpc/include/asm/reg_8xx.h
> +++ b/arch/powerpc/include/asm/reg_8xx.h
> @@ -17,6 +17,7 @@
>  #define SPRN_DC_DAT	570	/* Read-only data register */
>  
>  /* Misc Debug */
> +#define SPRN_ICR	148
>  #define SPRN_DPDR	630
>  #define SPRN_MI_CAM	816
>  #define SPRN_MI_RAM0	817
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 2cb5892..0f1f0ce 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -400,8 +400,16 @@ static inline int check_io_access(struct pt_regs *regs)
>  #define REASON_TRAP		0x20000
>  
>  #define single_stepping(regs)	((regs)->msr & MSR_SE)
> +#ifdef CONFIG_PPC_8xx
> +static inline void clear_single_step(struct pt_regs *regs)
> +{
> +	regs->msr &= ~MSR_SE;
> +	mfspr(SPRN_ICR);
> +}
> +#else
>  #define clear_single_step(regs)	((regs)->msr &= ~MSR_SE)
>  #endif
> +#endif
>  
>  #if defined(CONFIG_4xx)
>  int machine_check_4xx(struct pt_regs *regs)
> -- 
> 2.1.0