openthread: Fix OpenThread independence from Zephyr network.

If CONFIG_OPENTHREAD_SYS_INIT is enabled, OpenThread initialisation
should also consider running OpenThread automatically if
CONFIG_OPENTHREAD_MANUAL_START is disabled.

Removed also dependency on the `net_bytes_from_str` functions from
the openthread.h file. Now, in the OpenThread module, there is an
additional `openthread_utils.c/.h` file that can implement useful
utilities for the OpenThread platform. Currently, it implements
the `bytes_from_str` function to use it instead of
`net_bytes_from_str`.

Signed-off-by: Arkadiusz Balys <arkadiusz.balys@nordicsemi.no>

Author: ArekBalysNordic

modules/openthread/CMakeLists.txt

@@ -277,6 +277,7 @@ endif()
 zephyr_library_named(openthread_utils)
 zephyr_library_sources(
   openthread.c
+  openthread_utils.c
 )
 zephyr_library_sources_ifdef(CONFIG_OPENTHREAD_SHELL shell.c)
 zephyr_include_directories(include)

modules/openthread/include/openthread_utils.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_MODULES_OPENTHREAD_OPENTHREAD_UTILS_H_
+#define ZEPHYR_MODULES_OPENTHREAD_OPENTHREAD_UTILS_H_
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Convert a string representation of bytes into a buffer.
+ *
+ * This function parses a string containing hexadecimal byte values and fills
+ * the provided buffer with the corresponding bytes. The string may contain
+ * optional delimiters (such as spaces or colons) between byte values.
+ *
+ * @param buf      Pointer to the buffer where the parsed bytes will be stored.
+ * @param buf_len  Length of the buffer in bytes.
+ * @param src      Null-terminated string containing the hexadecimal byte values.
+ *
+ * @return 0 on success, or a negative value on error.
+ */
+int bytes_from_str(uint8_t *buf, int buf_len, const char *src);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_MODULES_OPENTHREAD_OPENTHREAD_UTILS_H_ */

modules/openthread/openthread.c

@@ -21,6 +21,7 @@ LOG_MODULE_REGISTER(net_openthread_platform, CONFIG_OPENTHREAD_PLATFORM_LOG_LEVE
 #include "platform/platform-zephyr.h"
 
 #include <openthread.h>
+#include <openthread_utils.h>
 
 #include <openthread/child_supervision.h>
 #include <openthread/cli.h>
@@ -182,15 +183,22 @@ static bool ot_setup_default_configuration(void)
 		return false;
 	}
 
-	net_bytes_from_str(xpanid.m8, 8, (char *)OT_XPANID);
+	if (bytes_from_str(xpanid.m8, 8, (char *)OT_XPANID) != 0) {
+		LOG_ERR("Failed to parse extended PAN ID");
+		return false;
+	}
 	error = otThreadSetExtendedPanId(openthread_instance, &xpanid);
 	if (error != OT_ERROR_NONE) {
 		LOG_ERR("Failed to set %s [%d]", "ext PAN ID", error);
 		return false;
 	}
 
 	if (strlen(OT_NETWORKKEY)) {
-		net_bytes_from_str(networkKey.m8, OT_NETWORK_KEY_SIZE, (char *)OT_NETWORKKEY);
+		if (bytes_from_str(networkKey.m8, OT_NETWORK_KEY_SIZE, (char *)OT_NETWORKKEY) !=
+		    0) {
+			LOG_ERR("Failed to parse network key");
+			return false;
+		}
 		error = otThreadSetNetworkKey(openthread_instance, &networkKey);
 		if (error != OT_ERROR_NONE) {
 			LOG_ERR("Failed to set %s [%d]", "network key", error);
@@ -485,5 +493,18 @@ void openthread_mutex_unlock(void)
 }
 
 #ifdef CONFIG_OPENTHREAD_SYS_INIT
-SYS_INIT(openthread_init, POST_KERNEL, CONFIG_OPENTHREAD_SYS_INIT_PRIORITY);
+static int openthread_sys_init(void)
+{
+	int error = openthread_init();
+
+	if (error == 0) {
+#ifndef CONFIG_OPENTHREAD_MANUAL_START
+		error = openthread_run();
+#endif
+	}
+
+	return error;
+}
+
+SYS_INIT(openthread_sys_init, POST_KERNEL, CONFIG_OPENTHREAD_SYS_INIT_PRIORITY);
 #endif /* CONFIG_OPENTHREAD_SYS_INIT */

modules/openthread/openthread_utils.c

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @file
+ *   This file provides utility functions for the OpenThread module.
+ *
+ */
+
+#include <stddef.h>
+#include <string.h>
+#include <ctype.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#include <openthread_utils.h>
+
+int bytes_from_str(uint8_t *buf, int buf_len, const char *src)
+{
+	if (!buf || !src) {
+		return -EINVAL;
+	}
+
+	size_t i;
+	size_t src_len = strlen(src);
+	char *endptr;
+
+	for (i = 0U; i < src_len; i++) {
+		if (!isxdigit((unsigned char)src[i]) && src[i] != ':') {
+			return -EINVAL;
+		}
+	}
+
+	(void)memset(buf, 0, buf_len);
+
+	for (i = 0U; i < (size_t)buf_len; i++) {
+		buf[i] = (uint8_t)strtol(src, &endptr, 16);
+		src = ++endptr;
+	}
+
+	return 0;
+}