Bluetooth: buf: Put command complete/status in sync buf pool

Why is it ok to use the sync pool?

Because command complete/status is processed in prio: that means on the
same stack as the `bt_recv()` call from the driver.

Why does it fix the issue?

Because the complete/status event goes into a pool that is guaranteed to
have one free buffer any time `bt_recv()` is not executing.

Since the driver is the one calling bt_recv(), it (hopefully) will
finish one `bt_recv()` before starting another one.

Fixes #78223

Co-authored-by: Aleksander Wasaznik <[email protected]>
Signed-off-by: Aleksander Wasaznik <[email protected]>
Signed-off-by: Jonathan Rico <[email protected]>
(cherry picked from commit 6d5cce6)
Signed-off-by: Vinayak Kariappa Chettimada <[email protected]>

Author: 2 people

subsys/bluetooth/host/buf.c

@@ -14,20 +14,12 @@
 
 #include <zephyr/bluetooth/hci.h>
 
-#if defined(CONFIG_BT_CONN)
-#if defined(CONFIG_BT_ISO)
-#define MAX_EVENT_COUNT CONFIG_BT_MAX_CONN + CONFIG_BT_ISO_MAX_CHAN
-#else
-#define MAX_EVENT_COUNT CONFIG_BT_MAX_CONN
-#endif /* CONFIG_BT_ISO */
-#elif defined(CONFIG_BT_ISO)
-#define MAX_EVENT_COUNT CONFIG_BT_ISO_MAX_CHAN
-#endif /* CONFIG_BT_CONN */
-
-#if defined(CONFIG_BT_CONN) || defined(CONFIG_BT_ISO)
-#define NUM_COMLETE_EVENT_SIZE BT_BUF_EVT_SIZE(                        \
-	sizeof(struct bt_hci_cp_host_num_completed_packets) +          \
-	MAX_EVENT_COUNT * sizeof(struct bt_hci_handle_count))
+/* Events have a length field of 1 byte. This size fits all events.
+ *
+ * It's true that we don't put all kinds of events there (yet). However, the
+ * command complete event has an arbitrary payload, depending on opcode.
+ */
+#define SYNC_EVT_SIZE (BT_BUF_RESERVE + BT_HCI_EVT_HDR_SIZE + 255)
 
 /* Pool for RX HCI buffers that are always freed by `bt_recv`
  * before it returns.
@@ -37,9 +29,7 @@
  * the HCI transport to fill buffers in parallel with `bt_recv`
  * consuming them.
  */
-#define SYNC_EVT_SIZE NUM_COMLETE_EVENT_SIZE
 NET_BUF_POOL_FIXED_DEFINE(sync_evt_pool, 1, SYNC_EVT_SIZE, sizeof(struct bt_buf_data), NULL);
-#endif /* CONFIG_BT_CONN || CONFIG_BT_ISO */
 
 NET_BUF_POOL_FIXED_DEFINE(discardable_pool, CONFIG_BT_BUF_EVT_DISCARDABLE_COUNT,
 			  BT_BUF_EVT_SIZE(CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE),
@@ -96,9 +86,11 @@ struct net_buf *bt_buf_get_evt(uint8_t evt, bool discardable,
 	switch (evt) {
 #if defined(CONFIG_BT_CONN) || defined(CONFIG_BT_ISO)
 	case BT_HCI_EVT_NUM_COMPLETED_PACKETS:
+#endif /* CONFIG_BT_CONN || CONFIG_BT_ISO */
+	case BT_HCI_EVT_CMD_STATUS:
+	case BT_HCI_EVT_CMD_COMPLETE:
 		buf = net_buf_alloc(&sync_evt_pool, timeout);
 		break;
-#endif /* CONFIG_BT_CONN || CONFIG_BT_ISO */
 	default:
 		if (discardable) {
 			buf = net_buf_alloc(&discardable_pool, timeout);