Bluetooth: Host: Fix redundant ACL Rx buffer allocation

HCI ACL Rx buffer count is not required in addition, the
calculated BT_BUF_ACL_RX_COUNT is sufficient for L2CAP
recombination.

But it is required to have additional Rx buffers for the
HCI ACL Rx that can happen due to the generated HCI Host
Number of Completed packets events.

Fixes commit d382fca ("Bluetooth: Controller: Fix HCI
command buffer allocation failure").

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>

Author: cvinayak

include/zephyr/bluetooth/buf.h

@@ -151,8 +151,20 @@ static inline enum bt_buf_type bt_buf_type_from_h4(uint8_t h4_type, enum bt_buf_
  * re-assembly into, and if all links are re-assembling, there will be no buffer
  * available for the HCI driver to allocate from.
  */
-#define BT_BUF_ACL_RX_COUNT_EXTRA CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA
-#define BT_BUF_ACL_RX_COUNT       (1 + BT_BUF_ACL_RX_COUNT_EXTRA)
+#define BT_BUF_ACL_RX_COUNT_RESERVED     1
+
+/* Host will block unreferencing one Rx buffer per active ACL connection and generate HCI Host
+ * Number of Completed packets for the rest. This means new HCI data packets will be generated by
+ * the Controller.
+ */
+#define BT_BUF_ACL_RX_COUNT_BLOCKED_MIN  1
+#define BT_BUF_ACL_RX_COUNT_BLOCKED_MAX  CONFIG_BT_MAX_CONN
+
+/* To avoid deadlock account for maximum Rx buffers blocked in the Host */
+#define BT_BUF_ACL_RX_COUNT_EXTRA        MAX(BT_BUF_ACL_RX_COUNT_BLOCKED_MAX, \
+					     CONFIG_BT_BUF_ACL_RX_COUNT_EXTRA)
+/* ACL Rx Buffers being processed by the Host */
+#define BT_BUF_ACL_RX_COUNT              (BT_BUF_ACL_RX_COUNT_RESERVED + BT_BUF_ACL_RX_COUNT_EXTRA)
 #else
 #define BT_BUF_ACL_RX_COUNT_EXTRA 0
 #define BT_BUF_ACL_RX_COUNT       0

subsys/bluetooth/common/hci_common_internal.h

@@ -41,12 +41,9 @@ BUILD_ASSERT((CONFIG_BT_BUF_CMD_TX_COUNT == CONFIG_BT_CTLR_HCI_NUM_CMD_PKT_MAX),
  *
  * Host keeps the first, and subsequent, Rx buffers (that comes from the driver) for each connection
  * to do re-assembly into, up to the L2CAP SDU length required number of Rx buffers.
- * BT_BUF_ACL_RX_COUNT_EXTRA holds the application configured number of buffers across active
+ * BT_BUF_ACL_RX_COUNT_BLOCKED_MAX holds the application configured number of buffers across active
  * connections for recombination of HCI data packets to L2CAP SDUs.
  *
- * BT_BUF_HCI_EVT_RX_COUNT defines the number of available buffers reserved for "synchronous"
- * processing of HCI events like Number of Completed Packets, disconnection complete etc.
- *
  * BT_BUF_HCI_ACL_RX_COUNT defines the number of available buffers for Controller to Host data
  * flow control; keeping the application configured BT_BUF_ACL_RX_COUNT_EXTRA number of buffers
  * available for L2CAP recombination, and a reserved number of buffers for processing HCI events.
@@ -67,12 +64,13 @@ BUILD_ASSERT((CONFIG_BT_BUF_CMD_TX_COUNT == CONFIG_BT_CTLR_HCI_NUM_CMD_PKT_MAX),
  * control to restrict buffers required on resource constraint devices, i.e. if these events are not
  * processed "synchronous".
  */
-#define BT_BUF_HCI_EVT_RX_COUNT          1
-#define BT_BUF_HCI_ACL_RX_COUNT          (BT_BUF_RX_COUNT - BT_BUF_HCI_EVT_RX_COUNT - \
-					  BT_BUF_ACL_RX_COUNT_EXTRA)
+#define BT_BUF_HCI_ACL_RX_COUNT          (BT_BUF_RX_COUNT - BT_BUF_ACL_RX_COUNT_EXTRA)
+#define BT_BUF_HCI_ACL_RX_COUNT_EXTRA    (BT_BUF_HCI_ACL_RX_COUNT - BT_BUF_ACL_RX_COUNT_RESERVED - \
+					  BT_BUF_ACL_RX_COUNT_BLOCKED_MIN)
 #define BT_BUF_CMD_TX_HOST_NUM_CMPLT_PKT (BT_BUF_HCI_ACL_RX_COUNT)
 
 #else /* !CONFIG_BT_HCI_ACL_FLOW_CONTROL */
+#define BT_BUF_HCI_ACL_RX_COUNT_EXTRA    0
 #define BT_BUF_CMD_TX_HOST_NUM_CMPLT_PKT 0
 #endif /* !CONFIG_BT_HCI_ACL_FLOW_CONTROL */
 

subsys/bluetooth/host/buf.c

@@ -83,9 +83,9 @@ static void evt_pool_destroy(struct net_buf *buf)
 	buf_rx_freed_notify(BT_BUF_EVT);
 }
 
-NET_BUF_POOL_DEFINE(acl_in_pool, (BT_BUF_ACL_RX_COUNT_EXTRA + BT_BUF_HCI_ACL_RX_COUNT),
-		    BT_BUF_ACL_SIZE(CONFIG_BT_BUF_ACL_RX_SIZE), sizeof(struct bt_conn_rx),
-		    acl_in_pool_destroy);
+NET_BUF_POOL_DEFINE(acl_in_pool, (BT_BUF_ACL_RX_COUNT_EXTRA + BT_BUF_HCI_ACL_RX_COUNT_EXTRA),
+		    BT_BUF_ACL_SIZE(CONFIG_BT_BUF_ACL_RX_SIZE),
+		    sizeof(struct bt_conn_rx), acl_in_pool_destroy);
 
 NET_BUF_POOL_FIXED_DEFINE(evt_pool, CONFIG_BT_BUF_EVT_RX_COUNT, BT_BUF_EVT_RX_SIZE, 0,
 			  evt_pool_destroy);