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

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)