[MFI] Add ability to pass MFI audio through HCI (zephyrproject-rtos#27)

MFI audio packets now pass through HCI with the packet boundary flag set to '11' as suggested by the MFI spec

Author: kevin-whisper

include/zephyr/bluetooth/conn.h

@@ -1492,6 +1492,11 @@ struct bt_conn *bt_conn_create_br(const bt_addr_t *peer,
  */
 struct bt_conn *bt_conn_create_sco(const bt_addr_t *peer);
 
+// *** Whisper added for MFI. Register a callback for when audio packets are
+// received so the BLE stack knows where to pass them
+typedef void (*hci_mfi_audio_recv_cb_fn)(const uint8_t *data, uint8_t data_len);
+void bt_conn_mfi_audio_register_cb(hci_mfi_audio_recv_cb_fn mfi_audio_cb);
+
 #ifdef __cplusplus
 }
 #endif

subsys/bluetooth/controller/hci/hci.c

@@ -7946,9 +7946,14 @@ void hci_acl_encode(struct node_rx_pdu *node_rx, struct net_buf *buf)
 	switch (pdu_data->ll_id) {
 	case PDU_DATA_LLID_DATA_CONTINUE:
 	case PDU_DATA_LLID_DATA_START:
+	case PDU_DATA_LLID_RESV:
 		acl = (void *)net_buf_add(buf, sizeof(*acl));
 		if (pdu_data->ll_id == PDU_DATA_LLID_DATA_START) {
 			handle_flags = bt_acl_handle_pack(handle, BT_ACL_START);
+		} else if (pdu_data->ll_id == PDU_DATA_LLID_RESV) {
+			// MFI audio packets get sent over HCI with the packet boundary
+			// flag set to '11' which is normally unused
+			handle_flags = bt_acl_handle_pack(handle, BT_ACL_COMPLETE);
 		} else {
 			handle_flags = bt_acl_handle_pack(handle, BT_ACL_CONT);
 		}

subsys/bluetooth/controller/ll_sw/nordic/lll/lll_conn.c

@@ -1060,10 +1060,15 @@ static inline int isr_rx_pdu(struct lll_conn *lll, struct pdu_data *pdu_data_rx,
 
 					// if this is an audio packet and the primary transmit slot, deassert the sync signal
 					// for the ezairo
-					if((pdu_data_rx->ll_id == PDU_DATA_LLID_RESV) && 
-					   (pdu_data_rx->sn == 0) && 
-					    lll_mfi_audio_sync_deassert_cb) {
-						lll_mfi_audio_sync_deassert_cb();
+					if(pdu_data_rx->ll_id == PDU_DATA_LLID_RESV) {
+						// at the end of the packet, append the transmit slot type
+						pdu_data_rx->lldata[pdu_data_rx->len] = pdu_data_rx->sn;
+						pdu_data_rx->len = pdu_data_rx->len + 1;
+
+						// if this is the primary transmit slot, de-assert the sync signal for the ezairo
+						if((pdu_data_rx->sn == 0) && lll_mfi_audio_sync_deassert_cb) {
+							lll_mfi_audio_sync_deassert_cb();
+						}
 					}
 				}
 

subsys/bluetooth/controller/ll_sw/ull_conn.c

@@ -42,7 +42,6 @@
 #include "ull_conn_types.h"
 #include "ull_conn_iso_types.h"
 #include "ull_internal.h"
-#include "ull_mfi_audio_internal.h"
 #include "ull_sched_internal.h"
 #include "ull_chan_internal.h"
 #include "ull_conn_internal.h"
@@ -998,12 +997,6 @@ void ull_conn_setup(memq_link_t *rx_link, struct node_rx_hdr *rx)
 	}
 }
 
-// *** Whisper added for MFI
-static mfi_audio_recv_cb_fn ull_mfi_audio_cb = NULL;
-void ull_mfi_audio_register_cb(mfi_audio_recv_cb_fn mfi_audio_cb) {
-	ull_mfi_audio_cb = mfi_audio_cb;
-}
-
 int ull_conn_rx(memq_link_t *link, struct node_rx_pdu **rx)
 {
 	struct pdu_data *pdu_rx;
@@ -1057,19 +1050,9 @@ int ull_conn_rx(memq_link_t *link, struct node_rx_pdu **rx)
 		break;
 
 	case PDU_DATA_LLID_RESV:
-		// *** Whisper added for MFI.  MFI audio packets come in with the reserved
-		// LLID.  When we see these packets, pass the payload on to the mfi audio callback
-		// if the callback exists
-		if (ull_mfi_audio_cb) {
-			mfi_audio_slot_type_t slot_type;
-			if(pdu_rx->sn == 0) {
-				slot_type = MFI_AUDIO_SLOT_TYPE_PRIMARY;
-			} else {
-				slot_type = MFI_AUDIO_SLOT_TYPE_RETRANSMIT;
-			}
-			ull_mfi_audio_cb(pdu_rx->lldata, pdu_rx->len, slot_type);
-		}
-		// fallthrough (this existed before whisper modification)
+		// *** Whisper added for MFI.  Previously this would fallthrough and mark
+		// the node for release but now we added a break so the packet isn't discarded
+		break;
 	default:
 #if defined(CONFIG_BT_CTLR_LE_ENC)
 #if defined(CONFIG_BT_LL_SW_LLCP_LEGACY)

subsys/bluetooth/controller/ll_sw/ull_mfi_audio_internal.h

@@ -236,6 +236,12 @@ void bt_conn_reset_rx_state(struct bt_conn *conn)
 	conn->rx = NULL;
 }
 
+// *** Whisper added for MFI
+static hci_mfi_audio_recv_cb_fn bt_conn_mfi_audio_cb = NULL;
+void bt_conn_mfi_audio_register_cb(hci_mfi_audio_recv_cb_fn mfi_audio_cb) {
+	bt_conn_mfi_audio_cb = mfi_audio_cb;
+}
+
 static void bt_acl_recv(struct bt_conn *conn, struct net_buf *buf,
 			uint8_t flags)
 {
@@ -285,6 +291,17 @@ static void bt_acl_recv(struct bt_conn *conn, struct net_buf *buf,
 		net_buf_add_mem(conn->rx, buf->data, buf->len);
 		net_buf_unref(buf);
 		break;
+	// *** Whisper added for MFI.  BT_ACL_COMPLETE is a packet boundary flag of '11' which
+	// is how apple recommends transferring audio data over HCI.  this packet boundary flag
+	// is normally unused here
+	case BT_ACL_COMPLETE:
+		if(bt_conn_mfi_audio_cb) {
+			bt_conn_mfi_audio_cb(buf->data, buf->len);
+		}		
+		bt_conn_reset_rx_state(conn);
+		net_buf_unref(buf);
+		return;
+
 	default:
 		/* BT_ACL_START_NO_FLUSH and BT_ACL_COMPLETE are not allowed on
 		 * LE-U from Controller to Host.