thermal/core: Move parameter validation from __thermal_zone_get_temp to thermal_zone_get_temp

All callers of __thermal_zone_get_temp() already validated the
thermal zone parameters. Move validation to thermal_zone_get_temp()
where it is actually needed. Also add kernel documentation for
__thermal_zone_get_temp(), listing the requirement that the
function must be called with validated parameters and with thermal
device mutex held.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/thermal/thermal_helpers.c

@@ -64,6 +64,20 @@ get_thermal_instance(struct thermal_zone_device *tz,
 }
 EXPORT_SYMBOL(get_thermal_instance);
 
+/**
+ * __thermal_zone_get_temp() - returns the temperature of a thermal zone
+ * @tz: a valid pointer to a struct thermal_zone_device
+ * @temp: a valid pointer to where to store the resulting temperature.
+ *
+ * When a valid thermal zone reference is passed, it will fetch its
+ * temperature and fill @temp.
+ *
+ * Both tz and tz->ops must be valid pointers when calling this function,
+ * and the tz->ops->get_temp callback must be provided.
+ * The function must be called under tz->lock.
+ *
+ * Return: On success returns 0, an error code otherwise
+ */
 int __thermal_zone_get_temp(struct thermal_zone_device *tz, int *temp)
 {
 	int ret = -EINVAL;
@@ -73,9 +87,6 @@ int __thermal_zone_get_temp(struct thermal_zone_device *tz, int *temp)
 
 	lockdep_assert_held(&tz->lock);
 
-	if (!tz || IS_ERR(tz) || !tz->ops->get_temp)
-		return -EINVAL;
-
 	ret = tz->ops->get_temp(tz, temp);
 
 	if (IS_ENABLED(CONFIG_THERMAL_EMULATION) && tz->emul_temperature) {
@@ -114,13 +125,22 @@ int thermal_zone_get_temp(struct thermal_zone_device *tz, int *temp)
 {
 	int ret;
 
+	if (IS_ERR_OR_NULL(tz))
+		return -EINVAL;
+
 	mutex_lock(&tz->lock);
 
+	if (!tz->ops->get_temp) {
+		ret = -EINVAL;
+		goto unlock;
+	}
+
 	if (device_is_registered(&tz->device))
 		ret = __thermal_zone_get_temp(tz, temp);
 	else
 		ret = -ENODEV;
 
+unlock:
 	mutex_unlock(&tz->lock);
 
 	return ret;