pm: device_runtime: Optimize pm_device_runtime_usage

There is no point in using lock or semaphore to read current
usage counter as it may change after unlocking or giving
back the semaphore. Value can only be trusted in the controlled
environment (e.g. test).

Signed-off-by: Krzysztof Chruściński <[email protected]>

Author: nordic-krch

subsys/pm/device_runtime.c

@@ -563,25 +563,9 @@ bool pm_device_runtime_is_enabled(const struct device *dev)
 
 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;
 	}
 
-	if (atomic_test_bit(&dev->pm_base->flags, PM_DEVICE_FLAG_ISR_SAFE)) {
-		struct pm_device_isr *pm_sync = dev->pm_isr;
-		k_spinlock_key_t k = k_spin_lock(&pm_sync->lock);
-
-		usage = pm_sync->base.usage;
-
-		k_spin_unlock(&pm_sync->lock, k);
-	} else {
-		(void)k_sem_take(&pm->lock, K_FOREVER);
-		usage = pm->base.usage;
-		k_sem_give(&pm->lock);
-	}
-
-	return usage;
+	return dev->pm_base->usage;
 }