The patch below does not apply to the 6.12-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-6.12.y git checkout FETCH_HEAD git cherry-pick -x 267ee93c417e685d9f8e079e41c70ba6ee4df5a5 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025122923-amaretto-output-f3dc@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 267ee93c417e685d9f8e079e41c70ba6ee4df5a5 Mon Sep 17 00:00:00 2001 From: "j.turek" jakub.turek@elsta.tech Date: Sun, 21 Dec 2025 11:32:21 +0100 Subject: [PATCH] serial: xilinx_uartps: fix rs485 delay_rts_after_send

RTS line control with delay should be triggered when there is no more bytes in kfifo and hardware buffer is empty. Without this patch RTS control is scheduled right after feeding hardware buffer and this is too early.

RTS line may change state before hardware buffer is empty.

With this patch delayed RTS state change is triggered when function cdns_uart_handle_tx is called from cdns_uart_isr on CDNS_UART_IXR_TXEMPTY exactly when hardware completed transmission

Fixes: fccc9d9233f9 ("tty: serial: uartps: Add rs485 support to uartps driver") Cc: stable stable@kernel.org Link: https://patch.msgid.link/20251221103221.1971125-1-jakub.turek@elsta.tech Signed-off-by: Jakub Turek jakub.turek@elsta.tech Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c index c793fc74c26b..c593d20a1b5b 100644 --- a/drivers/tty/serial/xilinx_uartps.c +++ b/drivers/tty/serial/xilinx_uartps.c @@ -428,10 +428,17 @@ static void cdns_uart_handle_tx(void *dev_id) struct tty_port *tport = &port->state->port; unsigned int numbytes; unsigned char ch; + ktime_t rts_delay;

if (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port)) { /* Disable the TX Empty interrupt */ writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_IDR); + /* Set RTS line after delay */ + if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED) { + cdns_uart->tx_timer.function = &cdns_rs485_rx_callback; + rts_delay = ns_to_ktime(cdns_calc_after_tx_delay(cdns_uart)); + hrtimer_start(&cdns_uart->tx_timer, rts_delay, HRTIMER_MODE_REL); + } return; }

@@ -448,13 +455,6 @@ static void cdns_uart_handle_tx(void *dev_id)

/* Enable the TX Empty interrupt */ writel(CDNS_UART_IXR_TXEMPTY, cdns_uart->port->membase + CDNS_UART_IER); - - if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED && - (kfifo_is_empty(&tport->xmit_fifo) || uart_tx_stopped(port))) { - hrtimer_update_function(&cdns_uart->tx_timer, cdns_rs485_rx_callback); - hrtimer_start(&cdns_uart->tx_timer, - ns_to_ktime(cdns_calc_after_tx_delay(cdns_uart)), HRTIMER_MODE_REL); - } }

/**