Bluetooth: hci_ldisc: Add function to wait for characters to be sent

The hci UART line discipline sends its characters in a workqueue. Some
devices like the Marvell Bluetooth chips need to make sure that all
queued characters are sent before switching the baudrate. This adds
a function to synchronize with the workqueue.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/hci_ldisc.c

@@ -178,6 +178,7 @@ restart:
 		goto restart;
 
 	clear_bit(HCI_UART_SENDING, &hu->tx_state);
+	wake_up_bit(&hu->tx_state, HCI_UART_SENDING);
 }
 
 void hci_uart_init_work(struct work_struct *work)
@@ -213,6 +214,13 @@ int hci_uart_init_ready(struct hci_uart *hu)
 	return 0;
 }
 
+int hci_uart_wait_until_sent(struct hci_uart *hu)
+{
+	return wait_on_bit_timeout(&hu->tx_state, HCI_UART_SENDING,
+				   TASK_INTERRUPTIBLE,
+				   msecs_to_jiffies(2000));
+}
+
 /* ------- Interface to HCI layer ------ */
 /* Reset device */
 static int hci_uart_flush(struct hci_dev *hdev)