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; }