Bluetooth: Classic: L2CAP: Add connectionless data reception feature

Add a Kconfig `BT_L2CAP_CONNLESS` to enable the feature.

Add an API `bt_l2cap_br_connless_register()` to register the monitor
to receive the unicast connectionless data.

Add an API `bt_l2cap_br_connless_unregister()` to unregister the
registered callbacks.

Add an API `bt_l2cap_br_connless_send()` to send unicast
connectionless data.

Signed-off-by: Lyle Zhu <[email protected]>

Author: lylezhu2012

include/zephyr/bluetooth/classic/l2cap_br.h

@@ -133,6 +133,120 @@ int bt_l2cap_br_echo_req(struct bt_conn *conn, struct net_buf *buf);
  */
 int bt_l2cap_br_echo_rsp(struct bt_conn *conn, uint8_t identifier, struct net_buf *buf);
 
+/**
+ * @brief Connectionless data channel callback structure.
+ *
+ * This structure is used for tracking the connectionless data channel frames.
+ * It is registered with the help of the bt_l2cap_br_connless_register() API.
+ * It's permissible to register multiple instances of this @ref bt_l2cap_br_connless_cb type,
+ * in case different modules of an application are interested in tracking the connectionless
+ * data channel frames.
+ */
+struct bt_l2cap_br_connless_cb {
+	/** @brief Register PSM.
+	 *
+	 *  For BR, possible values:
+	 *
+	 *  The PSM field is at least two octets in length. All PSM values shall have the least
+	 *  significant bit of the most significant octet equal to 0 and the least significant bit
+	 *  of all other octets equal to 1.
+	 *
+	 *  0               Any connectionless data channel frame will be notified.
+	 *
+	 *  0x0001-0x0eff   Standard, Bluetooth SIG-assigned fixed values.
+	 *
+	 *  > 0x1000        Dynamically allocated. May be pre-set by the
+	 *                  application before server registration (not
+	 *                  recommended however), or auto-allocated by the
+	 *                  stack if the app gave 0 as the value.
+	 */
+	uint16_t psm;
+
+	/** Required minimum security level */
+	bt_security_t sec_level;
+
+	/**
+	 * @brief A connectionless channel data has been received.
+	 *
+	 * This callback notifies the application of a connectionless channel data has been
+	 * received.
+	 *
+	 * @param conn The ACL connection object.
+	 * @param psm Protocol/Service Multiplexer.
+	 * @param buf Received connectionless channel data.
+	 */
+	void (*recv)(struct bt_conn *conn, uint16_t psm, struct net_buf *buf);
+
+	/** @internal Internally used field for list handling */
+	sys_snode_t _node;
+};
+
+/**
+ * @brief Register connectionless data channel callbacks.
+ *
+ * Register callbacks to monitor and receive connectionless data channel frames.
+ * This allows the application to receive data sent to a specific PSM without
+ * establishing a connection.
+ *
+ * @param cb Callback struct. Must point to memory that remains valid.
+ *           The PSM field must be set to the desired Protocol/Service Multiplexer
+ *           value, or 0 to receive all connectionless data frames.
+ *
+ * @retval 0 Success.
+ * @retval -EINVAL If @p cb is NULL, has invalid PSM value, has invalid `recv` callback,
+ *                 or has invalid security level.
+ * @retval -EEXIST If a callback with the same PSM was already registered.
+ */
+int bt_l2cap_br_connless_register(struct bt_l2cap_br_connless_cb *cb);
+
+/**
+ * @brief Unregister connectionless data channel callbacks.
+ *
+ * Unregister callbacks that are used to monitor and receive connectionless data channel frames.
+ *
+ * @param cb Registered cb.
+ *
+ * @retval 0 Success.
+ * @retval -EINVAL If @p cb is NULL.
+ * @retval -ENOENT if @p cb was not registered.
+ */
+int bt_l2cap_br_connless_unregister(struct bt_l2cap_br_connless_cb *cb);
+
+/**
+ *  @brief L2CAP connectionless SDU header size.
+ */
+#define BT_L2CAP_CONNLESS_SDU_HDR_SIZE 2
+
+/**
+ *  @brief Headroom needed for outgoing L2CAP PDU format within a connectionless data channel.
+ */
+#define BT_L2CAP_CONNLESS_RESERVE BT_L2CAP_BUF_SIZE(BT_L2CAP_CONNLESS_SDU_HDR_SIZE)
+
+/**
+ * @brief Send data over connectionless data channel
+ *
+ * Send data over a connectionless data channel. This function allows sending data to
+ * a specific PSM without establishing the L2CAP channel connection.
+ *
+ * The application is required to have reserved @ref BT_L2CAP_CONNLESS_RESERVE bytes
+ * in the buffer before sending.
+ *
+ * @param conn Connection object.
+ * @param psm Protocol/Service Multiplexer identifying the destination service.
+ * @param buf Buffer containing the data to be sent. The application is required to
+ *            have reserved enough headroom in the buffer for the L2CAP header.
+ *
+ * @retval 0 Success.
+ * @retval -EINVAL If @p conn or @p buf is NULL, @p psm is invalid, the reference counter of @p buf
+ *                 != 1, the head room of @p buf is less than @ref BT_L2CAP_CONNLESS_RESERVE, or
+ *                 the `buf->user_data_size` is less than the size of `struct closure`.
+ * @return -ENOTSUP If the connectionless reception feature is unsupported by remote.
+ * @return -ENOTCONN If the L2CAP channel with connectionless channel is not found.
+ * @return -EMSGSIZE If the data size exceeds the peer's connectionless channel MTU.
+ * @retval -ESHUTDOWN If the L2CAP channel with connectionless channel is NULL in low level.
+ */
+int bt_l2cap_br_connless_send(struct bt_conn *conn, uint16_t psm, struct net_buf *buf);
+
 #ifdef __cplusplus
 }
 #endif

subsys/bluetooth/host/classic/Kconfig

@@ -44,6 +44,12 @@ config BT_MAX_SCO_CONN
 	  Maximum number of simultaneous Bluetooth synchronous connections
 	  supported. The minimum (and default) number is 1.
 
+config BT_L2CAP_CONNLESS
+	bool "Bluetooth L2CAP connectionless data reception [EXPERIMENTAL]"
+	select EXPERIMENTAL
+	help
+	  This option enables Bluetooth L2CAP connectionless data reception
+
 config BT_L2CAP_RET
 	bool "Bluetooth L2CAP retransmission mode [EXPERIMENTAL]"
 	select EXPERIMENTAL