The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 2790ce23951f0c497810c44ad60a126a59c8d84c # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025040348-sudoku-backspace-0802@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2790ce23951f0c497810c44ad60a126a59c8d84c Mon Sep 17 00:00:00 2001 From: Cheick Traore cheick.traore@foss.st.com Date: Thu, 20 Mar 2025 16:25:40 +0100 Subject: [PATCH] serial: stm32: do not deassert RS485 RTS GPIO prematurely

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 4c97965ec43b..ad06b760cfca 100644 --- 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);