nimble/transport: Add internal flow control

This adds support for internal flow control that can be implemented by
transports that work on multi-core systems (e.g. nRF5340).

nimble/controller/src/ble_ll_conn.c

@@ -3269,6 +3269,10 @@ ble_ll_conn_rx_data_pdu(struct os_mbuf *rxpdu, struct ble_mbuf_hdr *hdr)
 
     /* Free buffer */
 conn_rx_data_pdu_end:
+#if MYNEWT_VAL(BLE_TRANSPORT_INT_FLOW_CTL)
+    ble_transport_int_flow_ctl_put();
+#endif
+
 #if MYNEWT_VAL(BLE_LL_CFG_FEAT_CTRL_TO_HOST_FLOW_CONTROL)
     /* Need to give credit back if we allocated one for this PDU */
     if (hdr->rxinfo.flags & BLE_MBUF_HDR_F_CONN_CREDIT) {
@@ -3329,6 +3333,16 @@ ble_ll_conn_rx_isr_end(uint8_t *rxbuf, struct ble_mbuf_hdr *rxhdr)
         alloc_rxpdu = false;
     }
 
+#if MYNEWT_VAL(BLE_TRANSPORT_INT_FLOW_CTL)
+    /* Do not alloc PDU if there are no free buffers in transport. We'll nak
+     * this PDU in LL.
+     */
+    if (alloc_rxpdu && BLE_LL_LLID_IS_DATA(hdr_byte) && (rx_pyld_len > 0) &&
+        !ble_transport_int_flow_ctl_get()) {
+        alloc_rxpdu = false;
+    }
+#endif
+
 #if MYNEWT_VAL(BLE_LL_CFG_FEAT_CTRL_TO_HOST_FLOW_CONTROL)
     /*
      * If flow control is enabled, we need to have credit available for each

nimble/transport/include/nimble/transport.h

@@ -48,6 +48,12 @@ void ble_transport_free(void *buf);
 /* Register put callback on acl_from_ll mbufs (for ll-hs flow control) */
 int ble_transport_register_put_acl_from_ll_cb(os_mempool_put_fn *cb);
 
+#if MYNEWT_VAL(BLE_TRANSPORT_INT_FLOW_CTL)
+/* To be implemented if transport supports internal flow control between cores */
+extern int ble_transport_int_flow_ctl_get(void);
+extern void ble_transport_int_flow_ctl_put(void);
+#endif
+
 #ifdef __cplusplus
 }
 #endif

nimble/transport/nrf5340/syscfg.yml

@@ -0,0 +1,20 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#  http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#
+
+syscfg.defs:
+    BLE_TRANSPORT_INT_FLOW_CTL: 1

nimble/transport/src/transport.c

@@ -152,30 +152,33 @@ ble_transport_acl_put(struct os_mempool_ext *mpe, void *data, void *arg)
 {
     struct os_mbuf *om;
     struct os_mbuf_pkthdr *pkthdr;
+    bool do_put;
+    bool from_ll;
     os_error_t err;
 
     om = data;
     pkthdr = OS_MBUF_PKTHDR(om);
 
-    switch (pkthdr->omp_flags & OMP_FLAG_FROM_MASK) {
-    case OMP_FLAG_FROM_LL:
-        if (transport_put_acl_from_ll_cb) {
-            return transport_put_acl_from_ll_cb(mpe, data, arg);
-        }
-        break;
-    case OMP_FLAG_FROM_HS:
-        break;
-    default:
-        assert(0);
-        break;
+    do_put = true;
+    from_ll = (pkthdr->omp_flags & OMP_FLAG_FROM_MASK) == OMP_FLAG_FROM_LL;
+    err = 0;
+
+    if (from_ll && transport_put_acl_from_ll_cb) {
+        err = transport_put_acl_from_ll_cb(mpe, data, arg);
+        do_put = false;
     }
 
-    err = os_memblock_put_from_cb(&mpe->mpe_mp, data);
-    if (err) {
-        return err;
+    if (do_put) {
+        err = os_memblock_put_from_cb(&mpe->mpe_mp, data);
     }
 
-    return 0;
+#if MYNEWT_VAL(BLE_TRANSPORT_INT_FLOW_CTL)
+    if (from_ll && !err) {
+        ble_transport_int_flow_ctl_put();
+    }
+#endif
+
+    return err;
 }
 
 void