[PATCH 3.11 115/198] watchdog: ath79_wdt: avoid spurious restarts on AR934x

[Luis Henriques]

3.11.10.13 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gabor Juhos <juhosg at openwrt.org>

commit 23afeb613ec0e10aecfae7838a14d485db62ac52 upstream.

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 at openwrt.org>
Reviewed-by: Guenter Roeck <linux at roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim at iguana.be>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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 37cb09b27b63..c97a47ca8971 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/init.h>
@@ -91,6 +92,15 @@ 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);
-- 
1.9.1