[PATCH] powerpc: allow opting out of WATCHDOG_RESET() from timer interrupt

[PATCH] powerpc: allow opting out of WATCHDOG_RESET() from timer interrupt

[Rasmus Villemoes]

When using CONFIG_(SPL_)WDT, the watchdog_reset function is a lot more
complicated than just poking a few SOC-specific registers - it
involves accessing all kinds of global data, and if the interrupt
happens at the wrong time (say, in the middle of an WATCHDOG_RESET()
call from ordinary code), that can end up corrupting said global data.

Also, having WATCHDOG_RESET() called automatically from the timer
interrupt runs counter to the idea of a watchdog device - if the board
runs into an infinite loops with interrupts still enabled, the
watchdog will never fire.

Allow the board to opt out of this behaviour by setting
CONFIG_SYS_WATCHDOG_FREQ to 0 - as that setting is currently
nonsensical, it cannot affect any existing boards.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
---
 arch/powerpc/lib/interrupts.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/lib/interrupts.c b/arch/powerpc/lib/interrupts.c
index 64ee0cc210..23ac5bca1e 100644
--- a/arch/powerpc/lib/interrupts.c
+++ b/arch/powerpc/lib/interrupts.c
@@ -79,7 +79,7 @@ void timer_interrupt(struct pt_regs *regs)
 	timestamp++;
 
 #if defined(CONFIG_WATCHDOG) || defined (CONFIG_HW_WATCHDOG)
-	if ((timestamp % (CONFIG_SYS_WATCHDOG_FREQ)) == 0)
+	if (CONFIG_SYS_WATCHDOG_FREQ && (timestamp % (CONFIG_SYS_WATCHDOG_FREQ)) == 0)
 		WATCHDOG_RESET ();
 #endif    /* CONFIG_WATCHDOG || CONFIG_HW_WATCHDOG */
 
-- 
2.23.0

[PATCH v2] powerpc: allow opting out of WATCHDOG_RESET() from timer interrupt

[Rasmus Villemoes]

When using CONFIG_(SPL_)WDT, the watchdog_reset function is a lot more
complicated than just poking a few SOC-specific registers - it
involves accessing all kinds of global data, and if the interrupt
happens at the wrong time (say, in the middle of an WATCHDOG_RESET()
call from ordinary code), that can end up corrupting said global data.

Also, having WATCHDOG_RESET() called automatically from the timer
interrupt runs counter to the idea of a watchdog device - if the board
runs into an infinite loops with interrupts still enabled, the
watchdog will never fire.

Allow the board to opt out of this behaviour by setting
CONFIG_SYS_WATCHDOG_FREQ to 0 - as that setting is currently
nonsensical, it cannot affect any existing boards.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
---
v2: add comment explaining the semantics of setting CONFIG_SYS_WATCHDOG_FREQ to 0.

 arch/powerpc/lib/interrupts.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/lib/interrupts.c b/arch/powerpc/lib/interrupts.c
index 64ee0cc210..b213e40578 100644
--- a/arch/powerpc/lib/interrupts.c
+++ b/arch/powerpc/lib/interrupts.c
@@ -79,7 +79,12 @@ void timer_interrupt(struct pt_regs *regs)
 	timestamp++;
 
 #if defined(CONFIG_WATCHDOG) || defined (CONFIG_HW_WATCHDOG)
-	if ((timestamp % (CONFIG_SYS_WATCHDOG_FREQ)) == 0)
+	/*
+	 * Setting CONFIG_SYS_WATCHDOG_FREQ to 0 can be used to
+	 * disable calling WATCHDOG_RESET() from the timer interrupt
+	 * function.
+	 */
+	if (CONFIG_SYS_WATCHDOG_FREQ && (timestamp % (CONFIG_SYS_WATCHDOG_FREQ)) == 0)
 		WATCHDOG_RESET ();
 #endif    /* CONFIG_WATCHDOG || CONFIG_HW_WATCHDOG */
 
-- 
2.23.0

[PATCH v2] powerpc: allow opting out of WATCHDOG_RESET() from timer interrupt

[Wolfgang Denk]

Dear Rasmus Villemoes,

In message <20200318151651.2510-1-rasmus.villemoes@prevas.dk> you wrote:
> When using CONFIG_(SPL_)WDT, the watchdog_reset function is a lot more
> complicated than just poking a few SOC-specific registers - it
> involves accessing all kinds of global data, and if the interrupt
> happens at the wrong time (say, in the middle of an WATCHDOG_RESET()
> call from ordinary code), that can end up corrupting said global data.
>
> Also, having WATCHDOG_RESET() called automatically from the timer
> interrupt runs counter to the idea of a watchdog device - if the board
> runs into an infinite loops with interrupts still enabled, the
> watchdog will never fire.
>
> Allow the board to opt out of this behaviour by setting
> CONFIG_SYS_WATCHDOG_FREQ to 0 - as that setting is currently
> nonsensical, it cannot affect any existing boards.
>
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

If such a change gets implemented, it should at least be made
consistently, i. e. not only in arch/powerpc/lib/interrupts.c but
also in the timer_interrupt() handler in drivers/timer/mpc83xx_timer.c
and in dtimer_interrupt() in arch/m68k/lib/time.c and wherever else
similar code may exist.


Only changing one plase is not a good idea.

And please add some documentation also to the README.

Thanks.

Best regards,

Wolfgang Denk

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