eatt: Add support for manual EATT connection

Introduce ble_eatt_connect() API to allow manual setup EATT.
This change enables explicit control over EATT channel creation.

The function validates the connection handle and requested channel
count, supports requesting all channels by passing 0

Add declaration of ble_eatt_connect() to the ble_att.h header.

Author: szymon-czapracki

nimble/host/include/host/ble_att.h

@@ -355,6 +355,18 @@ uint16_t ble_att_preferred_mtu(void);
  */
 int ble_att_set_preferred_mtu(uint16_t mtu);
 
+/**
+ * Manually establish L2CAP Enhanced Connection
+ *
+ * @param conn_handle           ACL connection handle
+ * @param chan_num              Number of channels to establish
+ *
+ * @return                      0 on success;
+ *                              NimBLE host core return code on unexpected
+ *                              error.
+ */
+int ble_eatt_connect(uint16_t conn_handle, uint8_t chan_num);
+
 #ifdef __cplusplus
 }
 #endif

nimble/host/src/ble_eatt.c

@@ -130,9 +130,9 @@ ble_eatt_find(uint16_t conn_handle, uint16_t cid)
         if (eatt->conn_handle == conn_handle) {
             for (i = 0; i < MYNEWT_VAL(BLE_EATT_CHAN_PER_CONN); i++) {
                 if (eatt->chan[i] && eatt->chan[i]->scid == cid) {
-            return eatt;
-        }
-    }
+                    return eatt;
+                }
+            }
         }
     }
     return NULL;
@@ -245,7 +245,7 @@ ble_eatt_wakeup_cb(struct ble_npl_event *ev)
         for (i = 0; i < MYNEWT_VAL(BLE_EATT_CHAN_PER_CONN); i++) {
             if (eatt->chan[i] != NULL) {
                 ble_l2cap_get_chan_info(eatt->chan[i], &info);
-        ble_eatt_tx(eatt->conn_handle, info.dcid, txom);
+                ble_eatt_tx(eatt->conn_handle, info.dcid, txom);
                 break;
             }
         }
@@ -641,6 +641,52 @@ ble_eatt_start(uint16_t conn_handle)
     ble_npl_eventq_put(ble_hs_evq_get(), &eatt->setup_ev);
 }
 
+int
+ble_eatt_connect(uint16_t conn_handle, uint8_t chan_num)
+{
+    int rc;
+    uint8_t free_channels;
+    struct ble_eatt *eatt;
+    struct ble_gap_conn_desc desc;
+
+    rc = ble_gap_conn_find(conn_handle, &desc);
+    assert(rc == 0);
+
+    eatt = ble_eatt_find_by_conn_handle(conn_handle);
+    if (!eatt) {
+        eatt = ble_eatt_alloc();
+        if (!eatt) {
+            BLE_EATT_LOG_ERROR("ble_eatt_connect: Can't allocate EATT\n");
+            return BLE_HS_ENOMEM;
+        }
+        eatt->conn_handle = conn_handle;
+    }
+
+    if (chan_num > MYNEWT_VAL(BLE_EATT_CHAN_PER_CONN)) {
+        BLE_EATT_LOG_WARN("ble_eatt_connect: Invalid channel number\n");
+        return BLE_HS_EREJECT;
+    }
+
+    /* Get number of free channels for this connection */
+    free_channels =
+        MYNEWT_VAL(BLE_EATT_CHAN_PER_CONN) - ble_eatt_used_channels(conn_handle);
+
+    /* Connect all channels if invoked with 0 & all channels are free */
+    if (chan_num == 0 && free_channels == MYNEWT_VAL(BLE_EATT_CHAN_PER_CONN)) {
+        eatt->channels_to_connect = MYNEWT_VAL(BLE_EATT_CHAN_PER_CONN);
+    } else if (chan_num < free_channels) {
+        eatt->channels_to_connect = chan_num;
+    } else {
+        BLE_EATT_LOG_ERROR("ble_eatt_connect: Invalid channel number\n");
+        return BLE_HS_ENOMEM;
+    }
+
+    /* Setup EATT */
+    ble_npl_eventq_put(ble_hs_evq_get(), &eatt->setup_ev);
+
+    return 0;
+}
+
 void
 ble_eatt_init(ble_eatt_att_rx_fn att_rx_cb)
 {