[PATCH] watchdog: ath79_wdt: avoid spurious restarts on AR934x

[PATCH] watchdog: ath79_wdt: avoid spurious restarts on AR934x

[Gabor Juhos]

On some AR934x based systems, where the frequency of
the AHB bus is relatively high, the built-in watchdog
causes a spurious restart when it gets enabled.

The possible cause of these restarts is that the timeout
value written into the TIMER register does not reaches
the hardware in time.

Add an explicit delay into the ath79_wdt_enable function
to avoid the spurious restarts.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: <stable@vger.kernel.org>
---
 drivers/watchdog/ath79_wdt.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/watchdog/ath79_wdt.c b/drivers/watchdog/ath79_wdt.c
index 399c3fd..0e67d96 100644
--- a/drivers/watchdog/ath79_wdt.c
+++ b/drivers/watchdog/ath79_wdt.c
@@ -20,6 +20,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/bitops.h>
+#include <linux/delay.h>
 #include <linux/errno.h>
 #include <linux/fs.h>
 #include <linux/io.h>
@@ -90,6 +91,15 @@ static inline void ath79_wdt_keepalive(void)
 static inline void ath79_wdt_enable(void)
 {
 	ath79_wdt_keepalive();
+
+	/*
+	 * Updating the TIMER register requires a few microseconds
+	 * on the AR934x SoCs at least. Use a small delay to ensure
+	 * that the TIMER register is updated within the hardware
+	 * before enabling the watchdog.
+	 */
+	udelay(2);
+
 	ath79_wdt_wr(WDOG_REG_CTRL, WDOG_CTRL_ACTION_FCR);
 	/* flush write */
 	ath79_wdt_rr(WDOG_REG_CTRL);
-- 
1.7.10

Re: [PATCH] watchdog: ath79_wdt: avoid spurious restarts on AR934x

[Guenter Roeck]

On 04/16/2014 02:34 AM, Gabor Juhos wrote:
> On some AR934x based systems, where the frequency of
> the AHB bus is relatively high, the built-in watchdog
> causes a spurious restart when it gets enabled.
>
> The possible cause of these restarts is that the timeout
> value written into the TIMER register does not reaches
> the hardware in time.
>
> Add an explicit delay into the ath79_wdt_enable function
> to avoid the spurious restarts.
>
> Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
> Cc: <stable@vger.kernel.org>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

Re: [PATCH] watchdog: ath79_wdt: avoid spurious restarts on AR934x

[Wim Van Sebroeck]

Hi Gabor,

> On some AR934x based systems, where the frequency of
> the AHB bus is relatively high, the built-in watchdog
> causes a spurious restart when it gets enabled.
> 
> The possible cause of these restarts is that the timeout
> value written into the TIMER register does not reaches
> the hardware in time.
> 
> Add an explicit delay into the ath79_wdt_enable function
> to avoid the spurious restarts.
> 
> Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
> Cc: <stable@vger.kernel.org>
> ---
>  drivers/watchdog/ath79_wdt.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/watchdog/ath79_wdt.c b/drivers/watchdog/ath79_wdt.c
> index 399c3fd..0e67d96 100644
> --- a/drivers/watchdog/ath79_wdt.c
> +++ b/drivers/watchdog/ath79_wdt.c
> @@ -20,6 +20,7 @@
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>  
>  #include <linux/bitops.h>
> +#include <linux/delay.h>
>  #include <linux/errno.h>
>  #include <linux/fs.h>
>  #include <linux/io.h>
> @@ -90,6 +91,15 @@ static inline void ath79_wdt_keepalive(void)
>  static inline void ath79_wdt_enable(void)
>  {
>  	ath79_wdt_keepalive();
> +
> +	/*
> +	 * Updating the TIMER register requires a few microseconds
> +	 * on the AR934x SoCs at least. Use a small delay to ensure
> +	 * that the TIMER register is updated within the hardware
> +	 * before enabling the watchdog.
> +	 */
> +	udelay(2);
> +
>  	ath79_wdt_wr(WDOG_REG_CTRL, WDOG_CTRL_ACTION_FCR);
>  	/* flush write */
>  	ath79_wdt_rr(WDOG_REG_CTRL);

This patch has been added to linux-watchdog-next.

Kind regards,
Wim.