Bluetooth: Support BT_RECV_WORKQ_BT with Zephyr LL

This patch allows selecting the combination of `CONFIG_BT_RECV_WORKQ_BT`
and `BT_LL_SW_SPLIT`. The implementation of `bt_recv_prio` is copied
from `hci_raw.c`. This ensures the order of packets is the same as when
the controller's `hci_driver.c` is off-chip and sends HCI over UART.

Without this patch, the Zephyr LL driver will duplicate some events on
behalf of `hci_core`. This duplication is not wanted when
`CONFIG_BT_RECV_WORKQ_BT=y`.

The above mentioned duplication is not sound and is evidenced in logged
warnings, e.g. in `tests/bsim/bluetooth/host/l2cap/stress` with
`CONFIG_BT_RECV_WORKQ_BT=y` logging "no transition".

This patch is a step towards the deprecation of
`CONFIG_BT_RECV_BLOCKING`. `CONFIG_BT_RECV_BLOCKING` is complicated and
tightly coupled to `hci_core`. In the future, removing
`CONFIG_BT_RECV_BLOCKING` will give a cleaner separation between
`hci_core` and the drivers and allow `hci_core` to evolve without
changes spilling out into the drivers.

Signed-off-by: Aleksander Wasaznik <[email protected]>

subsys/bluetooth/controller/hci/hci_driver.c

@@ -81,6 +81,30 @@ static sys_slist_t hbuf_pend;
 static int32_t hbuf_count;
 #endif
 
+#if !defined(CONFIG_BT_RECV_BLOCKING)
+/* Copied here from `hci_raw.c`, which would be used in
+ * conjunction with this driver when serializing HCI over wire.
+ * This serves as a converter from the more complicated
+ * `CONFIG_BT_RECV_BLOCKING` API to the normal single-receiver
+ * `bt_recv` API.
+ */
+int bt_recv_prio(struct net_buf *buf)
+{
+	if (bt_buf_get_type(buf) == BT_BUF_EVT) {
+		struct bt_hci_evt_hdr *hdr = (void *)buf->data;
+		uint8_t evt_flags = bt_hci_evt_get_flags(hdr->evt);
+
+		if ((evt_flags & BT_HCI_EVT_FLAG_RECV_PRIO) &&
+		    (evt_flags & BT_HCI_EVT_FLAG_RECV)) {
+			/* Avoid queuing the event twice */
+			return 0;
+		}
+	}
+
+	return bt_recv(buf);
+}
+#endif /* CONFIG_BT_RECV_BLOCKING */
+
 #if defined(CONFIG_BT_CTLR_ISO)
 
 #define SDU_HCI_HDR_SIZE (BT_HCI_ISO_HDR_SIZE + BT_HCI_ISO_TS_DATA_HDR_SIZE)

subsys/bluetooth/host/hci_core.c

@@ -3881,6 +3881,7 @@ int bt_recv(struct net_buf *buf)
 	}
 }
 
+#if defined(CONFIG_BT_RECV_BLOCKING)
 int bt_recv_prio(struct net_buf *buf)
 {
 	bt_monitor_send(bt_monitor_opcode(buf), buf->data, buf->len);
@@ -3891,6 +3892,7 @@ int bt_recv_prio(struct net_buf *buf)
 
 	return 0;
 }
+#endif /* CONFIG_BT_RECV_BLOCKING */
 
 int bt_hci_driver_register(const struct bt_hci_driver *drv)
 {