watchdog: pretimeout: add option to select a pretimeout governor in runtime

The change converts watchdog device attribute "pretimeout_governor" from
read-only to read-write type to allow users to select a desirable
watchdog pretimeout governor in runtime, e.g.

  % echo -n panic > /sys/..../watchdog/watchdog0/pretimeout

To get this working a list of registered pretimeout governors is created
and a new helper function watchdog_pretimeout_governor_set() is exported
to watchdog_dev.c.

If a selected governor is gone, a watchdog device pretimeout notification
is delegated to a default built-in pretimeout governor.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

1 files changed, 14 insertions, 1 deletions

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index d2d0b5e37a35..3fdbe0ab1365 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -497,7 +497,20 @@ static ssize_t pretimeout_governor_show(struct device *dev,
 
 	return watchdog_pretimeout_governor_get(wdd, buf);
 }
-static DEVICE_ATTR_RO(pretimeout_governor);
+
+static ssize_t pretimeout_governor_store(struct device *dev,
+					 struct device_attribute *attr,
+					 const char *buf, size_t count)
+{
+	struct watchdog_device *wdd = dev_get_drvdata(dev);
+	int ret = watchdog_pretimeout_governor_set(wdd, buf);
+
+	if (!ret)
+		ret = count;
+
+	return ret;
+}
+static DEVICE_ATTR_RW(pretimeout_governor);
 
 static umode_t wdt_is_visible(struct kobject *kobj, struct attribute *attr,
 				int n)