device: allow initializing any device

Remove restrictions from device_init by allowing to perform device
initialization if the device state flags it being not initialized.
This makes the API usable in contexts where device_deinit has been
called before.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

include/zephyr/device.h

@@ -825,13 +825,12 @@ __syscall bool device_is_ready(const struct device *dev);
  *
  * A device whose initialization was deferred (by marking it as
  * ``zephyr,deferred-init`` on devicetree) needs to be initialized manually via
- * this call. Note that only devices whose initialization was deferred can be
- * initialized via this call - one can not try to initialize a non
- * initialization deferred device that failed initialization with this call.
+ * this call. De-initialized devices can also be initialized again via this
+ * call.
  *
  * @param dev device to be initialized.
  *
- * @retval -ENOENT If device was not found - or isn't a deferred one.
+ * @retval -EALREADY Device is already initialized.
  * @retval -errno For other errors.
  */
 __syscall int device_init(const struct device *dev);

kernel/init.c

@@ -378,18 +378,11 @@ static void z_sys_init_run_level(enum init_level level)
 
 int z_impl_device_init(const struct device *dev)
 {
-	const struct device *devs;
-	size_t devc;
-
-	devc = z_device_get_all_static(&devs);
-
-	for (const struct device *dev_ = devs; dev_ < (devs + devc); dev_++) {
-		if ((dev_ == dev) && ((dev->flags & DEVICE_FLAG_INIT_DEFERRED) != 0U)) {
-			return do_device_init(dev);
-		}
+	if (dev->state->initialized) {
+		return -EALREADY;
 	}
 
-	return -ENOENT;
+	return do_device_init(dev);
 }
 
 #ifdef CONFIG_USERSPACE