tty: serial: fsl_lpuart: disable transmitter before changing RS485 related registers

commit f5cb528d6441eb860250a2f085773aac4f44085e upstream.

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 77efa7ee6eda29aa9a1d92740430327ffe416eb8..9f9fc733eb2c1fd5c5d918717ea34dfe86034495 100644 (file)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1483,6 +1483,19 @@ 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) {
@@ -1502,6 +1515,10 @@ 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;
 }