Re: [PATCH v1] watchdog: sama5d4_wdt: Reset delay on start

From: Guenter Roeck
Date: Thu Mar 03 2016 - 07:10:22 EST


On 03/03/2016 02:29 AM, Romain Izard wrote:
If the internal counter is not refreshed when the watchdog is started
for the first time, the watchdog will trigger very rapidly. For example,
opening /dev/watchdog without writing in it will immediately trigger a
reboot, instead of waiting for the delay to expire.

To avoid this problem, reload the timer on opening the watchdog device.

Command: "while sleep 5; do echo 1; done > /dev/watchdog"
Before: system reset
After: the watchdog runs correctly

Signed-off-by: Romain Izard <romain.izard.pro@xxxxxxxxx>

Subject might better read "ping watchdog on start" or similar.

Does the watchdog have to be pinged before it is enabled ?
I am a bit concerned that there may still be a 125 uS window
during which the system could restart.

Thanks,
Guenter

---
drivers/watchdog/sama5d4_wdt.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/watchdog/sama5d4_wdt.c b/drivers/watchdog/sama5d4_wdt.c
index a49634cdc1cc..e162fe140ae1 100644
--- a/drivers/watchdog/sama5d4_wdt.c
+++ b/drivers/watchdog/sama5d4_wdt.c
@@ -15,6 +15,7 @@
#include <linux/platform_device.h>
#include <linux/reboot.h>
#include <linux/watchdog.h>
+#include <linux/delay.h>

#include "at91sam9_wdt.h"

@@ -58,6 +59,8 @@ static int sama5d4_wdt_start(struct watchdog_device *wdd)
reg = wdt_read(wdt, AT91_WDT_MR);
reg &= ~AT91_WDT_WDDIS;
wdt_write(wdt, AT91_WDT_MR, reg);
+ udelay(125); /* > 4 cycles at 32,768 Hz */
+ wdt_write(wdt, AT91_WDT_CR, AT91_WDT_KEY | AT91_WDT_WDRSTT);

return 0;
}