watchdog: pretimeout: add pretimeout_available_governors attribute

The change adds an option to a user with CONFIG_WATCHDOG_SYSFS and
CONFIG_WATCHDOG_PRETIMEOUT_GOV enabled to get information about all
registered watchdog pretimeout governors by reading watchdog device
attribute named "pretimeout_available_governors".

Signed-off-by: Vladimir Zapolskiy <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Reviewed-by: Wolfram Sang <[e-mail]>
Tested-by: Wolfram Sang <[e-mail]>
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

drivers/watchdog/watchdog_dev.c

···
 }
 static DEVICE_ATTR_RO(state);
 
+static ssize_t pretimeout_available_governors_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	return watchdog_pretimeout_available_governors_get(buf);
+}
+static DEVICE_ATTR_RO(pretimeout_available_governors);
+
 static ssize_t pretimeout_governor_show(struct device *dev,
 					struct device_attribute *attr,
 					char *buf)
···
 	else if (attr == &dev_attr_pretimeout.attr &&
 		 !(wdd->info->options & WDIOF_PRETIMEOUT))
 		mode = 0;
-	else if (attr == &dev_attr_pretimeout_governor.attr &&
+	else if ((attr == &dev_attr_pretimeout_governor.attr ||
+		  attr == &dev_attr_pretimeout_available_governors.attr) &&
 		 (!(wdd->info->options & WDIOF_PRETIMEOUT) ||
 		  !IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_GOV)))
 		mode = 0;
···
 	&dev_attr_status.attr,
 	&dev_attr_nowayout.attr,
 	&dev_attr_pretimeout_governor.attr,
+	&dev_attr_pretimeout_available_governors.attr,
 	NULL,
 };
 

drivers/watchdog/watchdog_pretimeout.c

···
 	return NULL;
 }
 
+int watchdog_pretimeout_available_governors_get(char *buf)
+{
+	struct governor_priv *priv;
+	int count = 0;
+
+	mutex_lock(&governor_lock);
+
+	list_for_each_entry(priv, &governor_list, entry)
+		count += sprintf(buf + count, "%s\n", priv->gov->name);
+
+	mutex_unlock(&governor_lock);
+
+	return count;
+}
+
 int watchdog_pretimeout_governor_get(struct watchdog_device *wdd, char *buf)
 {
 	int count = 0;

drivers/watchdog/watchdog_pretimeout.h

···
 /* Interfaces to watchdog_dev.c */
 int watchdog_register_pretimeout(struct watchdog_device *wdd);
 void watchdog_unregister_pretimeout(struct watchdog_device *wdd);
+int watchdog_pretimeout_available_governors_get(char *buf);
 int watchdog_pretimeout_governor_get(struct watchdog_device *wdd, char *buf);
 int watchdog_pretimeout_governor_set(struct watchdog_device *wdd,
 				     const char *buf);
···
 
 static inline void watchdog_unregister_pretimeout(struct watchdog_device *wdd)
 {
+}
+
+static inline int watchdog_pretimeout_available_governors_get(char *buf)
+{
+	return -EINVAL;
 }
 
 static inline int watchdog_pretimeout_governor_get(struct watchdog_device *wdd,