bluetooth: host: add kconfig for synchronous buffer count

- adding kconfig for HCI synchronous cmds, or events responsble to
 manage host-controller credits to avoid discard complete event
 due to unavailability of synchronous buffer.
- Issue was present while working with usecases like Broadcast-BAP
 where more than 1 stream (SDU per BIS) sent to controller over HCI
 and controller sends NOCP events for both streams at the end of
 BIG sync anchor. The gap between two consecutive events in same BIG
 is within few usec range causes HCI driver to drop successive event
 while processing current and if not freed.

Signed-off-by: Nirav Agrawal <nirav.agrawal@nxp.com>

Author: nirav-agrawal

subsys/bluetooth/common/Kconfig

@@ -172,6 +172,19 @@ config BT_BUF_EVT_DISCARDABLE_COUNT
 	  it will not cause the allocation for other critical events to
 	  block and may even eliminate deadlocks in some cases.
 
+config BT_BUF_EVT_SYNCHRONOUS_COUNT
+	int "Number of synchronous HCI Event buffers"
+	range 1 $(UINT8_MAX)
+	# number of buffer require for bap-broadcast BIS counts
+	default BT_BAP_BROADCAST_SRC_STREAM_COUNT if BT_BAP_BROADCAST_SOURCE
+	default 1
+	help
+	  Number of buffers in a separate pool for events which the HCI
+	  stack depedent to manage it's command buffer queue, host to
+	  controller buffer credits etc. The events command_complete,
+	  number of command processed(nocp) etc considered under this
+	  event pool and processed on priority.
+
 config BT_BUF_CMD_TX_SIZE
 	int "Maximum support HCI Command buffer length"
 	default $(UINT8_MAX) if (BT_EXT_ADV || BT_CLASSIC || BT_ISO_CENTRAL || BT_CHANNEL_SOUNDING)

subsys/bluetooth/host/buf.c

@@ -64,7 +64,7 @@ static void iso_rx_freed_cb(void)
  * the HCI transport to fill buffers in parallel with `bt_recv`
  * consuming them.
  */
-NET_BUF_POOL_FIXED_DEFINE(sync_evt_pool, 1, SYNC_EVT_SIZE, 0, NULL);
+NET_BUF_POOL_FIXED_DEFINE(sync_evt_pool, CONFIG_BT_BUF_EVT_SYNCHRONOUS_COUNT, SYNC_EVT_SIZE, 0, NULL);
 
 NET_BUF_POOL_FIXED_DEFINE(discardable_pool, CONFIG_BT_BUF_EVT_DISCARDABLE_COUNT,
 			  BT_BUF_EVT_SIZE(CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE),