[PATCH 4.9 08/48] serial: stm32: fix software flow control transfer

[Greg Kroah-Hartman]

From: Valentin Caron <valentin.caron@xxxxxxxxxxx>

commit 037b91ec7729524107982e36ec4b40f9b174f7a2 upstream.

x_char is ignored by stm32_usart_start_tx() when xmit buffer is empty.

Fix start_tx condition to allow x_char to be sent.

Fixes: 48a6092fb41f ("serial: stm32-usart: Add STM32 USART Driver")
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Erwan Le Ray <erwan.leray@xxxxxxxxxxx>
Signed-off-by: Valentin Caron <valentin.caron@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220111164441.6178-3-valentin.caron@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/tty/serial/stm32-usart.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -389,7 +389,7 @@ static void stm32_start_tx(struct uart_p
 {
 	struct circ_buf *xmit = &port->state->xmit;
 
-	if (uart_circ_empty(xmit))
+	if (uart_circ_empty(xmit) && !port->x_char)
 		return;
 
 	stm32_transmit_chars(port);