subsys: add Kconfig for default boot protocol

Let combined builds choose Zigbee or Matter as the initial protocol when
no persisted settings entry exists yet.

Signed-off-by: Eduardo Montoya <eduardo.montoya@nordicsemi.no>

Author: edmont

include/zigbee/matter_protocol_state.h

@@ -14,10 +14,11 @@
  * @brief Persistent "which protocol is active" state for samples that host
  * both Matter and Zigbee on the same 802.15.4 radio.
  *
- * The application boots on Zigbee by default. Once Matter commissioning
- * completes, the state flips to Matter and is persisted so that subsequent
- * reboots resume Matter directly (and Zigbee stack initialization is skipped).
- * A factory reset resets the state back to Zigbee.
+ * The default protocol on first boot is selected by Kconfig (see
+ * @kconfig{CONFIG_ZIGBEE_MATTER_PROTOCOL_STATE_DEFAULT_PROTOCOL}). Once Matter
+ * commissioning completes, the state flips to Matter and is persisted so that
+ * subsequent reboots resume Matter directly (and Zigbee stack initialization
+ * is skipped). A factory reset resets the state back to Zigbee.
  */
 
 #include <stdbool.h>

subsys/lib/zigbee_matter_protocol_state/Kconfig

@@ -15,6 +15,28 @@ menuconfig ZIGBEE_MATTER_PROTOCOL_STATE
 
 if ZIGBEE_MATTER_PROTOCOL_STATE
 
+choice ZIGBEE_MATTER_PROTOCOL_STATE_DEFAULT_PROTOCOL
+	prompt "Default protocol on first boot"
+	default ZIGBEE_MATTER_PROTOCOL_STATE_DEFAULT_ZIGBEE
+	help
+	  Applied when no protocol state has been stored yet (factory-fresh
+	  device or after the settings entry was erased). Subsequent boots use
+	  the persisted value.
+
+config ZIGBEE_MATTER_PROTOCOL_STATE_DEFAULT_ZIGBEE
+	bool "Zigbee"
+	help
+	  Start on Zigbee: bring up the Zigbee stack and hand the 802.15.4
+	  radio to ZBOSS unless a previous run already persisted Matter.
+
+config ZIGBEE_MATTER_PROTOCOL_STATE_DEFAULT_MATTER
+	bool "Matter"
+	help
+	  Start on Matter: skip Zigbee stack start and hand the 802.15.4 radio
+	  to OpenThread unless a previous run already persisted Zigbee.
+
+endchoice
+
 module = ZIGBEE_MATTER_PROTOCOL_STATE
 module-str = Matter/Zigbee protocol state
 source "${ZEPHYR_BASE}/subsys/logging/Kconfig.template.log_config"

subsys/lib/zigbee_matter_protocol_state/matter_protocol_state.c

@@ -19,6 +19,7 @@ LOG_MODULE_REGISTER(matter_protocol_state, CONFIG_ZIGBEE_MATTER_PROTOCOL_STATE_L
 
 static atomic_t active_protocol = ATOMIC_INIT(PROTOCOL_ZIGBEE);
 static atomic_t state_initialized = ATOMIC_INIT(0);
+static bool protocol_loaded_from_settings;
 static K_MUTEX_DEFINE(init_mutex);
 
 static int protocol_state_load_direct_cb(const char *key, size_t len,
@@ -51,6 +52,7 @@ static int protocol_state_load_direct_cb(const char *key, size_t len,
 		return 0;
 	}
 
+	protocol_loaded_from_settings = true;
 	atomic_set(&active_protocol, (atomic_val_t)value);
 	return 0;
 }
@@ -79,6 +81,14 @@ int protocol_state_init(void)
 	(void)settings_load_subtree_direct(ZIGBEE_SETTINGS_SUBSYS_NAME,
 					   protocol_state_load_direct_cb, NULL);
 
+	if (!protocol_loaded_from_settings) {
+#if IS_ENABLED(CONFIG_ZIGBEE_MATTER_PROTOCOL_STATE_DEFAULT_MATTER)
+		atomic_set(&active_protocol, PROTOCOL_MATTER);
+#else
+		atomic_set(&active_protocol, PROTOCOL_ZIGBEE);
+#endif
+	}
+
 	atomic_set(&state_initialized, 1);
 
 	LOG_INF("Boot protocol: %s",