serial: stm32: do not deassert RS485 RTS GPIO prematurely

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>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index f5199fdecff278f63ed85587ceeeaaf2617c6a81..9b9981352b1e1a361fc4c45be0389b4c53cdf610 100644 (file)
--- 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 uart_port *port)
 {
        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);