[PATCH 6.13 21/23] serial: stm32: do not deassert RS485 RTS GPIO prematurely

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Cheick Traore <cheick.traore@foss.st.com>

commit 2790ce23951f0c497810c44ad60a126a59c8d84c upstream.

If stm32_usart_start_tx is called with an empty xmit buffer, RTS GPIO
could be deasserted prematurely, as bytes in TX FIFO are still
transmitting.
So this patch remove rts disable when xmit buffer is empty.

Fixes: d7c76716169d ("serial: stm32: Use TC interrupt to deassert GPIO RTS in RS485 mode")
Cc: stable <stable@kernel.org>
Signed-off-by: Cheick Traore <cheick.traore@foss.st.com>
Link: https://lore.kernel.org/r/20250320152540.709091-1-cheick.traore@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/serial/stm32-usart.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -965,10 +965,8 @@ static void stm32_usart_start_tx(struct
 {
 	struct tty_port *tport = &port->state->port;
 
-	if (kfifo_is_empty(&tport->xmit_fifo) && !port->x_char) {
-		stm32_usart_rs485_rts_disable(port);
+	if (kfifo_is_empty(&tport->xmit_fifo) && !port->x_char)
 		return;
-	}
 
 	stm32_usart_rs485_rts_enable(port);