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

[Gabriel Paubert]

On Thu, Aug 18, 2016 at 12:13:21PM +0200, Christophe Leroy wrote:
> 
> 
> 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.

Ok, I believe that systematically setting it is a mistake, but then I'm
always a bit nervous about screwing up timekeeping (it certainly is
always a very bad idea when you are driving telescopes).

    Gabriel