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

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

Le 18/08/2016 à 11:58, Gabriel Paubert a écrit :

quoted

On Thu, Aug 18, 2016 at 11:44:20AM +0200, Christophe Leroy wrote:

quoted

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