[3.13.y.z extended stable] Patch "watchdog: ath79_wdt: avoid spurious restarts on AR934x" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    watchdog: ath79_wdt: avoid spurious restarts on AR934x

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.5.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From d9237597f1900c16554e881def861f0ad799fed6 Mon Sep 17 00:00:00 2001
From: Gabor Juhos <juhosg at openwrt.org>
Date: Wed, 16 Apr 2014 11:34:41 +0200
Subject: watchdog: ath79_wdt: avoid spurious restarts on AR934x

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: Kamal Mostafa <kamal 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 9fa1f69..61098cd 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