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SubjectRe: [PATCH] powerpc/8xx: fix single_step debug
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Le 18/08/2016 à 11:58, Gabriel Paubert a écrit :
> 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

We could also unset TBF bit (TimeBase Freeze enable) in TBSCR register
(today it is set in arch/powerpc/platforms/8xx/m8xx_setup.c) but then it
would impact debug done with an external BDM system which expects the
decrementer and TB frozen when it freezes the execution.

Christophe


>
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.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

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