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 5135cdc0b664455b9d093df37e4777ebc829f16a..110d98fed7260ba2a1e981c123f6f7283cc6ba04 100644 (file)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1352,6 +1352,19 @@ static int lpuart32_config_rs485(struct uart_port *port,
 
        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);
 
        /* clear unsupported configurations */
@@ -1392,6 +1405,10 @@ static int lpuart32_config_rs485(struct uart_port *port,
        sport->port.rs485 = *rs485;
 
        lpuart32_write(&sport->port, modem, UARTMODIR);
+
+       if (ctrl & UARTCTRL_TE)
+               lpuart32_write(&sport->port, ctrl, UARTCTRL);
+
        return 0;
 }