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

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

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.

Christophe

quoted

Signed-off-by: Christophe Leroy <redacted>
---
 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