[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 at 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