openwrt/target/linux/ar71xx/patches-3.10/104-watchdog-ath79-wdt-avoid-spurious-restarts-on-AR934x.patch

From 2ff030d44672d745c5327b72463af43f5103e99b Mon Sep 17 00:00:00 2001
From: Gabor Juhos <juhosg@openwrt.org>
Date: Tue, 25 Mar 2014 17:07:46 +0100
Subject: [PATCH] watchdog: ath79-wdt: avoid spurious restarts on AR934x

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(+)

--- 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(v
 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);