In case runtime PM is not enabled (or not built-in), the get/put
functions always return 0 (instead of -ENOTSUP/-ENOSYS). When runtime PM
is disabled, a device is left into active state. Similarly, when device
runtime PM is not built-in, it is safe to assume that a device will
be active when it is called. If a user implements a custom solution, it
is its responsability to make sure that a device is active when using
it. For all these reasons, the -ENOTSUP/-ENOSYS are error codes that
should always be ignored by devices using get/put, since in practice it
means that: device is active, function is a no-op. The example below
illustrates how error handling is simplified:
```c
/* before: safe to ignore -ENOSYS/-ENOTSUP since device is active (we
* can continue)
*/
ret = pm_device_runtime_get(dev);
if ((ret < 0) && (ret != -ENOSYS) && (ret != -ENOTSUP)) {
return ret;
}
/* now */
ret = pm_device_runtime_get(dev);
if (ret < 0) {
return ret;
}
```
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
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