[PATCH V3 2/6] USB: serial: f81232: Add tx_empty function

["Ji-Ze Hong (Peter Hong)" <hpeter@gmail.com>]

Add tx_empty() function for F81232. Without this, console redirection will
get garbage data.

Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
---
Changelog:
v3:
	1. Modify return true when accessing device with error.

v2:
	1: Change check tx empty from UART_LSR_TEMT | UART_LSR_THRE to
	   UART_LSR_TEMT only. 

 drivers/usb/serial/f81232.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/usb/serial/f81232.c b/drivers/usb/serial/f81232.c
index c07d376c743d..793d0b30e347 100644
--- a/drivers/usb/serial/f81232.c
+++ b/drivers/usb/serial/f81232.c
@@ -685,6 +685,20 @@ static void f81232_dtr_rts(struct usb_serial_port *port, int on)
 		f81232_set_mctrl(port, 0, TIOCM_DTR | TIOCM_RTS);
 }
 
+static bool f81232_tx_empty(struct usb_serial_port *port)
+{
+	int status;
+	u8 tmp;
+
+	status = f81232_get_register(port, LINE_STATUS_REGISTER, &tmp);
+	if (!status) {
+		if ((tmp & UART_LSR_TEMT) != UART_LSR_TEMT)
+			return false;
+	}
+
+	return true;
+}
+
 static int f81232_carrier_raised(struct usb_serial_port *port)
 {
 	u8 msr;
@@ -820,6 +834,7 @@ static struct usb_serial_driver f81232_device = {
 	.tiocmget =		f81232_tiocmget,
 	.tiocmset =		f81232_tiocmset,
 	.tiocmiwait =		usb_serial_generic_tiocmiwait,
+	.tx_empty =		f81232_tx_empty,
 	.process_read_urb =	f81232_process_read_urb,
 	.read_int_callback =	f81232_read_int_callback,
 	.port_probe =		f81232_port_probe,
-- 
2.17.1