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

[ Upstream commit f5cb528d6441eb860250a2f085773aac4f44085e ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index e96354edff6e9ee1e5b76f02a586720c6a22b986..011f1759361329ae933783f46bf991eb9e202517 100644 (file)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1395,6 +1395,19 @@ 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) {
@@ -1414,6 +1427,10 @@ 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;
 }