pm: device_runtime: add an access function to get the usage counter

Add a pm_device_usage_get() to get the current usage counter.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

include/zephyr/pm/device_runtime.h

@@ -159,6 +159,17 @@ int pm_device_runtime_put_async(const struct device *dev, k_timeout_t delay);
  */
 bool pm_device_runtime_is_enabled(const struct device *dev);
 
+/**
+ * @brief Return the current device usage counter.
+ *
+ * @param dev Device instance.
+ *
+ * @returns the current usage counter.
+ * @retval -ENOTSUP If the device is not using runtime PM.
+ * @retval -ENOSYS If the runtime PM is not enabled at all.
+ */
+int pm_device_runtime_usage(const struct device *dev);
+
 #else
 
 static inline int pm_device_runtime_auto_enable(const struct device *dev)
@@ -205,6 +216,12 @@ static inline bool pm_device_runtime_is_enabled(const struct device *dev)
 	return false;
 }
 
+static inline int pm_device_runtime_usage(const struct device *dev)
+{
+	ARG_UNUSED(dev);
+	return -ENOSYS;
+}
+
 #endif
 
 /** @} */

subsys/pm/device_runtime.c

@@ -560,3 +560,19 @@ bool pm_device_runtime_is_enabled(const struct device *dev)
 
 	return pm && atomic_test_bit(&pm->flags, PM_DEVICE_FLAG_RUNTIME_ENABLED);
 }
+
+int pm_device_runtime_usage(const struct device *dev)
+{
+	struct pm_device *pm = dev->pm;
+	uint32_t usage;
+
+	if (!pm_device_runtime_is_enabled(dev)) {
+		return -ENOTSUP;
+	}
+
+	(void)k_sem_take(&pm->lock, K_FOREVER);
+	usage = pm->base.usage;
+	k_sem_give(&pm->lock);
+
+	return usage;
+}