thermal/core: Create a helper __thermal_cdev_update() without a lock

There is a need to have a helper function which updates cooling device
state from the governors code. With this change governor can use
lock and unlock while calling helper function. This avoid unnecessary
second time lock/unlock which was in previous solution present in
governor implementation. This new helper function must be called
with mutex 'cdev->lock' hold.

The changed been discussed and part of code presented in thread:
https://lore.kernel.org/linux-pm/20210419084536.25000-1-lukasz.luba@arm.com/

Co-developed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Link: https://lore.kernel.org/r/20210422114308.29684-2-lukasz.luba@arm.com

Author: lukaszluba-arm

drivers/thermal/thermal_core.h

@@ -66,6 +66,7 @@ static inline bool cdev_is_power_actor(struct thermal_cooling_device *cdev)
 }
 
 void thermal_cdev_update(struct thermal_cooling_device *);
+void __thermal_cdev_update(struct thermal_cooling_device *cdev);
 
 /**
  * struct thermal_trip - representation of a point in temperature domain

drivers/thermal/thermal_helpers.c

@@ -192,18 +192,11 @@ static void thermal_cdev_set_cur_state(struct thermal_cooling_device *cdev,
 	thermal_cooling_device_stats_update(cdev, target);
 }
 
-void thermal_cdev_update(struct thermal_cooling_device *cdev)
+void __thermal_cdev_update(struct thermal_cooling_device *cdev)
 {
 	struct thermal_instance *instance;
 	unsigned long target = 0;
 
-	mutex_lock(&cdev->lock);
-	/* cooling device is updated*/
-	if (cdev->updated) {
-		mutex_unlock(&cdev->lock);
-		return;
-	}
-
 	/* Make sure cdev enters the deepest cooling state */
 	list_for_each_entry(instance, &cdev->thermal_instances, cdev_node) {
 		dev_dbg(&cdev->device, "zone%d->target=%lu\n",
@@ -216,11 +209,25 @@ void thermal_cdev_update(struct thermal_cooling_device *cdev)
 
 	thermal_cdev_set_cur_state(cdev, target);
 
-	cdev->updated = true;
-	mutex_unlock(&cdev->lock);
 	trace_cdev_update(cdev, target);
 	dev_dbg(&cdev->device, "set to state %lu\n", target);
 }
+
+/**
+ * thermal_cdev_update - update cooling device state if needed
+ * @cdev:	pointer to struct thermal_cooling_device
+ *
+ * Update the cooling device state if there is a need.
+ */
+void thermal_cdev_update(struct thermal_cooling_device *cdev)
+{
+	mutex_lock(&cdev->lock);
+	if (!cdev->updated) {
+		__thermal_cdev_update(cdev);
+		cdev->updated = true;
+	}
+	mutex_unlock(&cdev->lock);
+}
 EXPORT_SYMBOL(thermal_cdev_update);
 
 /**