tests: kernel: device: Add tests for deferred init failure

These tests verify the expected returned value and device state for
error cases (-EALREADY, -errno) conform to the device_init()
documentation.

Signed-off-by: Loic Domaigne <tech@domaigne.com>

Author: ljd42

tests/kernel/device/app.overlay

@@ -66,6 +66,13 @@
 		zephyr,deferred-init;
 	};
 
+	fakedeferdriver@F9000000 {
+		compatible = "fakedeferdriver";
+		reg = <0xF9000000 0x2000>;
+		status = "okay";
+		zephyr,deferred-init;
+	};
+
 	fakedomain_0: fakedomain_0 {
 		compatible = "fakedomain";
 		status = "okay";

tests/kernel/device/src/main.c

@@ -24,6 +24,7 @@
 
 #define FAKEDEFERDRIVER0	DEVICE_DT_GET(DT_PATH(fakedeferdriver_e7000000))
 #define FAKEDEFERDRIVER1	DEVICE_DT_GET(DT_PATH(fakedeferdriver_e8000000))
+#define FAKEDEFERDRIVER2        DEVICE_DT_GET(DT_PATH(fakedeferdriver_f9000000))
 
 /* A device without init call */
 DEVICE_DEFINE(dummy_noinit, DUMMY_NOINIT, NULL, NULL, NULL, NULL,
@@ -39,6 +40,12 @@ DEVICE_DT_DEFINE(DT_INST(1, fakedeferdriver), NULL, NULL, NULL, NULL,
 	      POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT,
 	      &fakedeferdriverapi);
 
+/* fake devices used to test deferred initialization failure */
+static int fakedeferdriver_init(const struct device *dev);
+
+DEVICE_DT_DEFINE(DT_INST(2, fakedeferdriver), fakedeferdriver_init, NULL, NULL, NULL, POST_KERNEL,
+		 CONFIG_KERNEL_INIT_PRIORITY_DEFAULT, NULL);
+
 /**
  * @brief Test cases to verify device objects
  *
@@ -415,6 +422,38 @@ ZTEST(device, test_deferred_init)
 	zassert_true(device_is_ready(FAKEDEFERDRIVER0));
 }
 
+static int fakedeferdriver_init(const struct device *dev)
+{
+	return -EIO;
+}
+
+/**
+ * @brief Test deferred initialization error
+ *
+ * @details Verify device_init error cases and expected device states
+ *
+ * - case -errno: if the device initialization fails
+ * - case -EALREADY: if the device is already initialized.
+ *
+ * @see device_init
+ * @ingroup kernel_device_tests
+ */
+ZTEST(device, test_deferred_init_failure)
+{
+	int ret;
+	const struct device *dev = FAKEDEFERDRIVER2;
+
+	zassert_false(device_is_ready(dev));
+	ret = device_init(dev);
+	zassert_equal(ret, -EIO);
+	zassert_false(device_is_ready(dev));
+	zassert_equal(dev->state->init_res, EIO);
+
+	ret = device_init(dev);
+	zassert_equal(ret, -EALREADY);
+	zassert_equal(dev->state->init_res, EIO);
+}
+
 ZTEST(device, test_device_api)
 {
 	const struct device *dev;