[nrf fromtree] bluetooth: host: att: Implement disconnect on ATT timeout

The timeout state is local and can block new ATT operations, but does
not affect the remote side. Disconnecting the GATT connection upon ATT
timeout simplifies error handling for developers. This reduces rare
failure conditions to a common one, without needing special cases for
ATT timeouts.

Signed-off-by: Pavel Vasilyev <[email protected]>
(cherry picked from commit f712bde)

Author: PavelVPV

doc/connectivity/bluetooth/bluetooth-le-host.rst

@@ -274,6 +274,19 @@ over LE connections. A more detailed description of this layer and the
 API reference can be found in the
 :ref:`GATT API reference section <bt_gatt>`.
 
+ATT timeout
+-----------
+
+If the peer device does not respond to an ATT request (such as read or write)
+within the ATT timeout, the host will automatically initiate a disconnect. This
+simplifies error handling by reducing rare failure conditions to a common
+disconnection, allowing developers to manage unexpected disconnects without
+special cases for ATT timeouts.
+
+.. image:: img/att_timeout.svg
+  :align: center
+  :alt: ATT timeout
+
 Mesh
 ====
 

doc/connectivity/bluetooth/img/att_timeout.svg

@@ -96,6 +96,8 @@ Bluetooth
   * Added API :c:func:`bt_gatt_get_uatt_mtu` to get current Unenhanced ATT MTU of a given
     connection (experimental).
 
+  * The host now disconnects from the peer upon ATT timeout.
+
 * HCI Drivers
 
 Boards & SoC Support

doc/releases/release-notes-4.0.rst

@@ -3150,9 +3150,10 @@ static void att_timeout(struct k_work *work)
 	struct k_work_delayable *dwork = k_work_delayable_from_work(work);
 	struct bt_att_chan *chan = CONTAINER_OF(dwork, struct bt_att_chan,
 						timeout_work);
+	int err;
 
 	bt_addr_le_to_str(bt_conn_get_dst(chan->att->conn), addr, sizeof(addr));
-	LOG_ERR("ATT Timeout for device %s", addr);
+	LOG_ERR("ATT Timeout for device %s. Disconnecting...", addr);
 
 	/* BLUETOOTH SPECIFICATION Version 4.2 [Vol 3, Part F] page 480:
 	 *
@@ -3163,6 +3164,16 @@ static void att_timeout(struct k_work *work)
 	 * target device on this ATT Bearer.
 	 */
 	bt_att_disconnected(&chan->chan.chan);
+
+	/* The timeout state is local and can block new ATT operations, but does not affect the
+	 * remote side. Disconnecting the GATT connection upon ATT timeout simplifies error handling
+	 * for developers. This reduces rare failure conditions to a common one, allowing developers
+	 * to handle unexpected disconnections without needing special cases for ATT timeouts.
+	 */
+	err = bt_conn_disconnect(chan->chan.chan.conn, BT_HCI_ERR_REMOTE_USER_TERM_CONN);
+	if (err) {
+		LOG_ERR("Disconnecting failed (err %d)", err);
+	}
 }
 
 static struct bt_att_chan *att_get_fixed_chan(struct bt_conn *conn)