From: Valentin Caron <valentin.caron@foss.st.com> stable inclusion from linux-4.19.228 commit a41398a5a1a0dde794c65ef1fa6b2323e2db68bc -------------------------------- 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@vger.kernel.org> Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com> Signed-off-by: Valentin Caron <valentin.caron@foss.st.com> Link: https://lore.kernel.org/r/20220111164441.6178-3-valentin.caron@foss.st.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com> Signed-off-by: Laibin Qiu <qiulaibin@huawei.com> --- drivers/tty/serial/stm32-usart.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c index e8d7a7bb4339..f761e1038c34 100644 --- a/drivers/tty/serial/stm32-usart.c +++ b/drivers/tty/serial/stm32-usart.c @@ -506,7 +506,7 @@ static void stm32_start_tx(struct uart_port *port) { 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); -- 2.22.0