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

Le 18/08/2016 à 12:16, Gabriel Paubert a écrit :

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

quoted

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).

Indeed you are right, this should not happen. The issue is due to the 
fact that the bootloader set the TRE bit in the DER register.
So the fix is to be done in the boot loader.

Christophe