Bluetooth: BASS: Add support for dynamic registration of BASS

Added support for dynamic registration and unregistration of the
Broadcast Audio Scan Service (BASS) within the scan delegator.
This enables both scan delegator and BASS to be registered or
unregistered dynamically at runtime.

Signed-off-by: Babak Arisian <bbaa@demant.com>

doc/releases/migration-guide-4.0.rst

@@ -288,6 +288,17 @@ Bluetooth Audio
   is enabled and that all members are bonded, to comply with the requirements from the CSIP spec.
   (:github:`78877`)
 
+* The Broadcast Audio Scan Service (BASS) shall now be registered and unregistered dynamically
+  at runtime within the scan delegator. Two new APIs, :c:func:`bt_bap_scan_delegator_register()`
+  and :c:func:`bt_bap_scan_delegator_unregister()`, have been introduced to manage both BASS and
+  scan delegator registration and initialization dynamically. It should also be mentioned that
+  the previous callback registration function, :c:func:`bt_bap_scan_delegator_register_cb()` has
+  now been removed and merged with :c:func:`bt_bap_scan_delegator_register()`.
+  This change allows more flexibility when registering or unregistering scan delegator and BASS
+  related functionality without requiring build-time configuration. Existing need to be updated
+  to use these new APIs.
+  (:github:`78751`)
+
 Bluetooth Classic
 =================
 

include/zephyr/bluetooth/audio/bap.h

@@ -318,7 +318,7 @@ struct bt_bap_scan_delegator_recv_state {
 /**
  * @brief Struct to hold the Basic Audio Profile Scan Delegator callbacks
  *
- * These can be registered for usage with bt_bap_scan_delegator_register_cb().
+ * These can be registered for usage with bt_bap_scan_delegator_register().
  */
 struct bt_bap_scan_delegator_cb {
 	/**
@@ -2048,14 +2048,29 @@ int bt_bap_broadcast_sink_delete(struct bt_bap_broadcast_sink *sink);
 /** @} */ /* End of group bt_bap_broadcast_sink */
 
 /**
- * @brief Register the callbacks for the Basic Audio Profile Scan Delegator
+ * @brief Register the Basic Audio Profile Scan Delegator and BASS.
+ *
+ * Register the scan deligator and Broadcast Audio Scan Service (BASS)
+ * dynamically at runtime.
  *
  * Only one set of callbacks can be registered at any one time, and calling this function multiple
  * times will override any previously registered callbacks.
  *
  * @param cb Pointer to the callback struct
+ *
+ * @return 0 in case of success or negative value in case of error.
  */
-void bt_bap_scan_delegator_register_cb(struct bt_bap_scan_delegator_cb *cb);
+int bt_bap_scan_delegator_register(struct bt_bap_scan_delegator_cb *cb);
+
+/**
+ * @brief unregister the Basic Audio Profile Scan Delegator and BASS.
+ *
+ * Unregister the scan deligator and Broadcast Audio Scan Service (BASS)
+ * dynamically at runtime.
+ *
+ * @return 0 in case of success or negative value in case of error.
+ */
+int bt_bap_scan_delegator_unregister(void);
 
 /**
  * @brief Set the periodic advertising sync state to syncing

samples/bluetooth/bap_broadcast_sink/src/main.c

@@ -1308,8 +1308,13 @@ static int init(void)
 		return err;
 	}
 
+	err = bt_bap_scan_delegator_register(&scan_delegator_cbs);
+	if (err) {
+		printk("Scan delegator register failed (err %d)\n", err);
+		return err;
+	}
+
 	bt_bap_broadcast_sink_register_cb(&broadcast_sink_cbs);
-	bt_bap_scan_delegator_register_cb(&scan_delegator_cbs);
 	bt_le_per_adv_sync_cb_register(&bap_pa_sync_cb);
 	bt_le_scan_cb_register(&bap_scan_cb);
 

samples/bluetooth/cap_acceptor/src/cap_acceptor_broadcast.c

@@ -731,6 +731,13 @@ int init_cap_acceptor_broadcast(void)
 			.recv = broadcast_scan_recv,
 		};
 
+		err = bt_bap_scan_delegator_register(&scan_delegator_cbs);
+		if (err != 0) {
+			LOG_ERR("Scan delegator register failed (err %d)", err);
+
+			return err;
+		}
+
 		err = bt_bap_broadcast_sink_register_cb(&broadcast_sink_cbs);
 		if (err != 0) {
 			LOG_ERR("Failed to register BAP broadcast sink callbacks: %d", err);
@@ -739,7 +746,6 @@ int init_cap_acceptor_broadcast(void)
 		}
 
 		bt_cap_stream_ops_register(&broadcast_sink.broadcast_stream, &broadcast_stream_ops);
-		bt_bap_scan_delegator_register_cb(&scan_delegator_cbs);
 		bt_le_per_adv_sync_cb_register(&bap_pa_sync_cb);
 
 		if (IS_ENABLED(CONFIG_SAMPLE_SCAN_SELF)) {

subsys/bluetooth/audio/Kconfig.bap

@@ -211,6 +211,7 @@ config BT_BAP_SCAN_DELEGATOR
 	select BT_EXT_ADV
 	select BT_PER_ADV_SYNC
 	select BT_ISO_SYNC_RECEIVER
+	select BT_GATT_DYNAMIC_DB
 	depends on BT_BONDABLE
 	help
 	  This option enables support for the Scan Delegator role and the

subsys/bluetooth/audio/bap_scan_delegator.c

@@ -87,7 +87,16 @@ struct bt_bap_scan_delegator_inst {
 		[CONFIG_BT_BAP_SCAN_DELEGATOR_RECV_STATE_COUNT];
 };
 
-static bool conn_cb_registered;
+enum scan_delegator_flag {
+	SCAN_DELEGATOR_FLAG_REGISTERED_CONN_CB,
+	SCAN_DELEGATOR_FLAG_REGISTERED_SCAN_DELIGATOR,
+	SCAN_DELEGATOR_FLAG_REGISTERED_PA_SYNC_CB,
+
+	SCAN_DELEGATOR_FLAG_NUM,
+};
+
+static ATOMIC_DEFINE(scan_delegator_flags, SCAN_DELEGATOR_FLAG_NUM);
+
 static struct bt_bap_scan_delegator_inst scan_delegator;
 static struct bt_bap_scan_delegator_cb *scan_delegator_cbs;
 
@@ -325,9 +334,9 @@ static struct broadcast_assistant *get_bap_broadcast_assistant(struct bt_conn *c
 		}
 	}
 
-	if (!conn_cb_registered) {
+	if (!atomic_test_and_set_bit(scan_delegator_flags,
+				     SCAN_DELEGATOR_FLAG_REGISTERED_CONN_CB)) {
 		bt_conn_cb_register(&conn_cb);
-		conn_cb_registered = true;
 	}
 
 	return new;
@@ -1157,7 +1166,7 @@ static ssize_t read_recv_state(struct bt_conn *conn,
 		      read_recv_state, NULL, UINT_TO_POINTER(idx)), \
 	BT_AUDIO_CCC(recv_state_cfg_changed)
 
-BT_GATT_SERVICE_DEFINE(bass_svc,
+static struct bt_gatt_attr attr_bass_svc[] = {
 	BT_GATT_PRIMARY_SERVICE(BT_UUID_BASS),
 	BT_AUDIO_CHRC(BT_UUID_BASS_CONTROL_POINT,
 		      BT_GATT_CHRC_WRITE_WITHOUT_RESP | BT_GATT_CHRC_WRITE,
@@ -1170,10 +1179,58 @@ BT_GATT_SERVICE_DEFINE(bass_svc,
 	RECEIVE_STATE_CHARACTERISTIC(2)
 #endif /* CONFIG_BT_BAP_SCAN_DELEGATOR_RECV_STATE_COUNT > 2 */
 #endif /* CONFIG_BT_BAP_SCAN_DELEGATOR_RECV_STATE_COUNT > 1 */
-);
+};
 
-static int bt_bap_scan_delegator_init(void)
+static struct bt_gatt_service bass_svc = BT_GATT_SERVICE(attr_bass_svc);
+
+static int bass_register(void)
 {
+	int err;
+
+	err = bt_gatt_service_register(&bass_svc);
+	if (err) {
+		LOG_DBG("Failed to register BASS service (err %d)", err);
+		return err;
+	}
+
+	LOG_DBG("BASS service registered");
+
+	return 0;
+}
+
+static int bass_unregister(void)
+{
+	int err;
+
+	err = bt_gatt_service_unregister(&bass_svc);
+	if (err) {
+		LOG_DBG("Failed to unregister BASS service (err %d)", err);
+		return err;
+	}
+
+	LOG_DBG("BASS service unregistered");
+
+	return 0;
+}
+
+/****************************** PUBLIC API ******************************/
+int bt_bap_scan_delegator_register(struct bt_bap_scan_delegator_cb *cb)
+{
+	int err;
+
+	if (atomic_test_and_set_bit(scan_delegator_flags,
+				    SCAN_DELEGATOR_FLAG_REGISTERED_SCAN_DELIGATOR)) {
+		LOG_DBG("Scan delegator already registered");
+		return -EALREADY;
+	}
+
+	err = bass_register();
+	if (err) {
+		atomic_clear_bit(scan_delegator_flags,
+				 SCAN_DELEGATOR_FLAG_REGISTERED_SCAN_DELIGATOR);
+		return err;
+	}
+
 	/* Store the pointer to the first characteristic in each receive state */
 	scan_delegator.recv_states[0].attr = &bass_svc.attrs[3];
 	scan_delegator.recv_states[0].index = 0;
@@ -1186,17 +1243,43 @@ static int bt_bap_scan_delegator_init(void)
 #endif /* CONFIG_BT_BAP_SCAN_DELEGATOR_RECV_STATE_COUNT > 2 */
 #endif /* CONFIG_BT_BAP_SCAN_DELEGATOR_RECV_STATE_COUNT > 1 */
 
-	bt_le_per_adv_sync_cb_register(&pa_sync_cb);
+	if (!atomic_test_and_set_bit(scan_delegator_flags,
+				     SCAN_DELEGATOR_FLAG_REGISTERED_PA_SYNC_CB)) {
+		err = bt_le_per_adv_sync_cb_register(&pa_sync_cb);
+		if (err) {
+			atomic_clear_bit(scan_delegator_flags,
+					 SCAN_DELEGATOR_FLAG_REGISTERED_PA_SYNC_CB);
+			atomic_clear_bit(scan_delegator_flags,
+					 SCAN_DELEGATOR_FLAG_REGISTERED_SCAN_DELIGATOR);
+			return err;
+		}
+	}
+
+	scan_delegator_cbs = cb;
 
 	return 0;
 }
 
-SYS_INIT(bt_bap_scan_delegator_init, APPLICATION, CONFIG_KERNEL_INIT_PRIORITY_DEVICE);
-
-/****************************** PUBLIC API ******************************/
-void bt_bap_scan_delegator_register_cb(struct bt_bap_scan_delegator_cb *cb)
+int bt_bap_scan_delegator_unregister(void)
 {
-	scan_delegator_cbs = cb;
+	int err;
+
+	if (!atomic_test_and_clear_bit(scan_delegator_flags,
+				       SCAN_DELEGATOR_FLAG_REGISTERED_SCAN_DELIGATOR)) {
+		LOG_DBG("Scan delegator not yet registered");
+		return -EALREADY;
+	}
+
+	err = bass_unregister();
+	if (err) {
+		atomic_set_bit(scan_delegator_flags,
+			       SCAN_DELEGATOR_FLAG_REGISTERED_SCAN_DELIGATOR);
+		return err;
+	}
+
+	scan_delegator_cbs = NULL;
+
+	return 0;
 }
 
 int bt_bap_scan_delegator_set_pa_state(uint8_t src_id,

subsys/bluetooth/audio/shell/bap_scan_delegator.c

@@ -436,8 +436,19 @@ static int cmd_bap_scan_delegator_init(const struct shell *sh, size_t argc,
 	static bool registered;
 
 	if (!registered) {
-		bt_le_per_adv_sync_cb_register(&pa_sync_cb);
-		bt_bap_scan_delegator_register_cb(&scan_delegator_cb);
+		int err;
+
+		err = bt_bap_scan_delegator_register(&scan_delegator_cb);
+		if (err) {
+			shell_error(sh, "Failed to register scan delegator (err: %d)", err);
+			return -ENOEXEC;
+		}
+
+		err = bt_le_per_adv_sync_cb_register(&pa_sync_cb);
+		if (err) {
+			shell_error(sh, "Failed to register PA sync callbacks (err: %d)", err);
+			return -ENOEXEC;
+		}
 
 		registered = true;
 	}

tests/bluetooth/tester/src/audio/btp_bap_broadcast.c

@@ -1033,7 +1033,10 @@ uint8_t btp_bap_broadcast_sink_setup(const void *cmd, uint16_t cmd_len,
 	}
 
 	/* For Scan Delegator role */
-	bt_bap_scan_delegator_register_cb(&scan_delegator_cbs);
+	err = bt_bap_scan_delegator_register(&scan_delegator_cbs);
+	if (err != 0) {
+		return BTP_STATUS_FAILED;
+	}
 
 	/* For Broadcast Sink role */
 	bt_bap_broadcast_sink_register_cb(&broadcast_sink_cbs);

tests/bsim/bluetooth/audio/src/bap_broadcast_sink_test.c

@@ -642,6 +642,12 @@ static int init(void)
 		return err;
 	}
 
+	err = bt_bap_scan_delegator_register(&scan_delegator_cbs);
+	if (err) {
+		FAIL("Scan delegator register failed (err %d)\n", err);
+		return err;
+	}
+
 	/* Test invalid input */
 	err = bt_bap_broadcast_sink_register_cb(NULL);
 	if (err == 0) {
@@ -655,7 +661,6 @@ static int init(void)
 		return err;
 	}
 
-	bt_bap_scan_delegator_register_cb(&scan_delegator_cbs);
 	bt_le_per_adv_sync_cb_register(&bap_pa_sync_cb);
 	bt_le_scan_cb_register(&bap_scan_cb);
 

tests/bsim/bluetooth/audio/src/bap_scan_delegator_test.c

@@ -685,7 +685,12 @@ static int common_init(void)
 
 	printk("Bluetooth initialized\n");
 
-	bt_bap_scan_delegator_register_cb(&scan_delegator_cb);
+	err = bt_bap_scan_delegator_register(&scan_delegator_cb);
+	if (err) {
+		FAIL("Scan delegator register failed (err %d)\n", err);
+		return err;
+	}
+
 	bt_le_per_adv_sync_cb_register(&pa_sync_cb);
 
 	err = bt_le_adv_start(BT_LE_ADV_CONN_ONE_TIME, ad, AD_SIZE, NULL, 0);

tests/bsim/bluetooth/audio/src/cap_acceptor_test.c

@@ -774,10 +774,16 @@ static void init(void)
 			return;
 		}
 
+		err = bt_bap_scan_delegator_register(&scan_delegator_cbs);
+		if (err != 0) {
+			FAIL("Scan deligator register failed (err %d)\n", err);
+
+			return;
+		}
+
 		bt_bap_broadcast_sink_register_cb(&broadcast_sink_cbs);
 		bt_le_per_adv_sync_cb_register(&bap_pa_sync_cb);
 		bt_le_scan_cb_register(&bap_scan_cb);
-		bt_bap_scan_delegator_register_cb(&scan_delegator_cbs);
 
 		UNSET_FLAG(flag_broadcaster_found);
 		UNSET_FLAG(flag_broadcast_code);