FAILED: patch "[PATCH] tty: serial: fsl_lpuart: disable transmitter before changing" failed to apply to 5.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.4-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-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x f5cb528d6441eb860250a2f085773aac4f44085e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025040331-baking-headgear-81e4@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From f5cb528d6441eb860250a2f085773aac4f44085e Mon Sep 17 00:00:00 2001
From: Sherry Sun <sherry.sun@nxp.com>
Date: Wed, 12 Mar 2025 10:25:03 +0800
Subject: [PATCH] tty: serial: fsl_lpuart: disable transmitter before changing
 RS485 related registers

According to the LPUART reference manual, TXRTSE and TXRTSPOL of MODIR
register only can be changed when the transmitter is disabled.
So disable the transmitter before changing RS485 related registers and
re-enable it after the change is done.

Fixes: 67b01837861c ("tty: serial: lpuart: Add RS485 support for 32-bit uart flavour")
Cc: stable <stable@kernel.org>
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20250312022503.1342990-1-sherry.sun@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 91d02c55c470..203ec3b46304 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1484,6 +1484,19 @@ static int lpuart32_config_rs485(struct uart_port *port, struct ktermios *termio
 
 	unsigned long modem = lpuart32_read(&sport->port, UARTMODIR)
 				& ~(UARTMODIR_TXRTSPOL | UARTMODIR_TXRTSE);
+	u32 ctrl;
+
+	/* TXRTSE and TXRTSPOL only can be changed when transmitter is disabled. */
+	ctrl = lpuart32_read(&sport->port, UARTCTRL);
+	if (ctrl & UARTCTRL_TE) {
+		/* wait for the transmit engine to complete */
+		lpuart32_wait_bit_set(&sport->port, UARTSTAT, UARTSTAT_TC);
+		lpuart32_write(&sport->port, ctrl & ~UARTCTRL_TE, UARTCTRL);
+
+		while (lpuart32_read(&sport->port, UARTCTRL) & UARTCTRL_TE)
+			cpu_relax();
+	}
+
 	lpuart32_write(&sport->port, modem, UARTMODIR);
 
 	if (rs485->flags & SER_RS485_ENABLED) {
@@ -1503,6 +1516,10 @@ static int lpuart32_config_rs485(struct uart_port *port, struct ktermios *termio
 	}
 
 	lpuart32_write(&sport->port, modem, UARTMODIR);
+
+	if (ctrl & UARTCTRL_TE)
+		lpuart32_write(&sport->port, ctrl, UARTCTRL);
+
 	return 0;
 }