[nrf fromlist] drivers: bluetooth: hci: Add retries for IPC interface

Add HCI IPC retry handling in case of full IPC
queue. This mechanism improves reliability.

The ipc_service_send can return -ENOMEM in case
of full queue. If this happens the retries are
executed in order to wait for queue to empty
and not drop messages.
If the retry mechanism reaches maximum then
the error code is passed back to the host.

The change should improve the handling of
passing messages to full ipc and reduce
dropping of packets.

Upstream PR #: 85649

Signed-off-by: Dominik Chat <[email protected]>

Author: dchat-nordic

drivers/bluetooth/hci/Kconfig

@@ -40,6 +40,24 @@ config BT_HCI_IPC
 	  Bluetooth HCI driver for communication with another CPU
 	  using the IPC subsystem.
 
+config BT_HCI_IPC_SEND_RETRY_COUNT
+	int "HCI IPC send retry count"
+	depends on BT_HCI_IPC
+	default 3
+	help
+	  Number of times to retry sending a message via IPC.
+	  The retries occur in case of a failure to send a message
+	  through IPC (-ENOMEM returned by ipc_service_send).
+
+config BT_HCI_IPC_SEND_RETRY_DELAY_US
+	int "HCI IPC send retry delay (us)"
+	depends on BT_HCI_IPC
+	default 75
+	help
+	  Delay in microseconds between retries when sending a message via IPC.
+	  When a single tick (CONFIG_SYS_CLOCK_TICKS_PER_SEC) is bigger then
+	  the retry delay the k_busy_wait function is used. Set with care.
+
 config BT_SPI
 	bool
 	select SPI

drivers/bluetooth/hci/ipc.c

@@ -22,6 +22,14 @@ LOG_MODULE_REGISTER(bt_hci_driver);
 
 #define IPC_BOUND_TIMEOUT_IN_MS K_MSEC(1000)
 
+/* The retry of ipc_service_send function requires a small (tens of us) delay.
+ * In order to ensure proper delay k_usleep is used when the system clock is
+ * precise enough and available (CONFIG_SYS_CLOCK_TICKS_PER_SEC different than 0).
+ */
+#define USE_SLEEP_BETWEEN_IPC_RETRIES COND_CODE_0(CONFIG_SYS_CLOCK_TICKS_PER_SEC, \
+	(false), \
+	((USEC_PER_SEC / CONFIG_SYS_CLOCK_TICKS_PER_SEC) > CONFIG_BT_HCI_IPC_SEND_RETRY_DELAY_US))
+
 struct ipc_data {
 	bt_hci_recv_t recv;
 	struct ipc_ept hci_ept;
@@ -265,19 +273,35 @@ static int bt_ipc_send(const struct device *dev, struct net_buf *buf)
 		break;
 	default:
 		LOG_ERR("Unknown type %u", bt_buf_get_type(buf));
+		err = -ENOMSG;
 		goto done;
 	}
 	net_buf_push_u8(buf, pkt_indicator);
 
 	LOG_HEXDUMP_DBG(buf->data, buf->len, "Final HCI buffer:");
-	err = ipc_service_send(&data->hci_ept, buf->data, buf->len);
+
+	for (int retries = 0; retries < CONFIG_BT_HCI_IPC_SEND_RETRY_COUNT + 1; retries++) {
+		err = ipc_service_send(&data->hci_ept, buf->data, buf->len);
+		if ((err >= 0) || (err != -ENOMEM)) {
+			break;
+		}
+
+		if (USE_SLEEP_BETWEEN_IPC_RETRIES) {
+			k_usleep(CONFIG_BT_HCI_IPC_SEND_RETRY_DELAY_US);
+		} else {
+			k_busy_wait(CONFIG_BT_HCI_IPC_SEND_RETRY_DELAY_US);
+		}
+	}
+
 	if (err < 0) {
 		LOG_ERR("Failed to send (err %d)", err);
+	} else {
+		err = 0;
 	}
 
 done:
 	net_buf_unref(buf);
-	return 0;
+	return err;
 }
 
 static void hci_ept_bound(void *priv)