Re: [PATCH] powerpc/8xx: fix single_step debug

[Christophe Leroy]

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@xxxxxx>
> > ---
> >  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