[PATCH v9 1/3] watchdog: da9063: Fix setting/changing timeout

[Marco Felsch <m.felsch@pengutronix.de>]

If the timeout value is set more than once the DA9063 watchdog triggers
a reset signal which reset the system.

To update the timeout value we have to disable the watchdog, clear the
watchdog counter value and write the new timeout value to the watchdog.
Clearing the counter value is a feature to be on the safe side because the
data sheet doesn't describe the behaviour of the watchdog counter value
after a watchdog disabling-enable-sequence.

The patch is based on Philipp Zabel's previous patch.

Fixes: 5e9c16e37608 ("watchdog: Add DA9063 PMIC watchdog driver.")
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
---
 drivers/watchdog/da9063_wdt.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/da9063_wdt.c b/drivers/watchdog/da9063_wdt.c
index b17ac1bb1f28..c1216e61e64e 100644
--- a/drivers/watchdog/da9063_wdt.c
+++ b/drivers/watchdog/da9063_wdt.c
@@ -45,8 +45,31 @@ static unsigned int da9063_wdt_timeout_to_sel(unsigned int secs)
 	return DA9063_TWDSCALE_MAX;
 }
 
+static int da9063_wdt_disable_timer(struct da9063 *da9063)
+{
+	return regmap_update_bits(da9063->regmap, DA9063_REG_CONTROL_D,
+				  DA9063_TWDSCALE_MASK,
+				  DA9063_TWDSCALE_DISABLE);
+}
+
 static int _da9063_wdt_set_timeout(struct da9063 *da9063, unsigned int regval)
 {
+	int ret;
+
+	/*
+	 * The watchdog triggers a reboot if a timeout value is already
+	 * programmed because the timeout value combines two functions
+	 * in one: indicating the counter limit and starting the watchdog.
+	 * The watchdog must be disabled to be able to change the timeout
+	 * value if the watchdog is already running. Then we can set the
+	 * new timeout value which enables the watchdog again.
+	 */
+	ret = da9063_wdt_disable_timer(da9063);
+	if (ret)
+		return ret;
+
+	usleep_range(150, 300);
+
 	return regmap_update_bits(da9063->regmap, DA9063_REG_CONTROL_D,
 				  DA9063_TWDSCALE_MASK, regval);
 }
@@ -71,8 +94,7 @@ static int da9063_wdt_stop(struct watchdog_device *wdd)
 	struct da9063 *da9063 = watchdog_get_drvdata(wdd);
 	int ret;
 
-	ret = regmap_update_bits(da9063->regmap, DA9063_REG_CONTROL_D,
-				 DA9063_TWDSCALE_MASK, DA9063_TWDSCALE_DISABLE);
+	ret = da9063_wdt_disable_timer(da9063);
 	if (ret)
 		dev_alert(da9063->dev, "Watchdog failed to stop (err = %d)\n",
 			  ret);
-- 
2.17.0