Bluetooth: Add L2CAP RFC option if ERTM is enabled

When trying to establish a connection with Enhanced Retransmission mode
enabled, the RFC option needs to be added to the configuration.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/l2cap.c

@@ -1743,12 +1743,29 @@ static int l2cap_build_conf_req(struct sock *sk, void *data)
 {
 	struct l2cap_pinfo *pi = l2cap_pi(sk);
 	struct l2cap_conf_req *req = data;
+	struct l2cap_conf_rfc rfc = { .mode = L2CAP_MODE_BASIC };
 	void *ptr = req->data;
 
 	BT_DBG("sk %p", sk);
 
+	switch (pi->mode) {
+	case L2CAP_MODE_BASIC:
 		if (pi->imtu != L2CAP_DEFAULT_MTU)
 			l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, pi->imtu);
+		break;
+
+	case L2CAP_MODE_ERTM:
+		rfc.mode            = L2CAP_MODE_ERTM;
+		rfc.txwin_size      = L2CAP_DEFAULT_RX_WINDOW;
+		rfc.max_transmit    = L2CAP_DEFAULT_MAX_RECEIVE;
+		rfc.retrans_timeout = cpu_to_le16(L2CAP_DEFAULT_RETRANS_TO);
+		rfc.monitor_timeout = cpu_to_le16(L2CAP_DEFAULT_MONITOR_TO);
+		rfc.max_pdu_size    = cpu_to_le16(L2CAP_DEFAULT_MAX_RX_APDU);
+
+		l2cap_add_conf_opt(&ptr, L2CAP_CONF_RFC,
+					sizeof(rfc), (unsigned long) &rfc);
+		break;
+	}
 
 	/* FIXME: Need actual value of the flush timeout */
 	//if (flush_to != L2CAP_DEFAULT_FLUSH_TO)