tty: serial: imx: fix rs485 rx after tx

Since commit 79d0224f6bf2 ("tty: serial: imx: Handle RS485 DE signal
active high") RS485 reception no longer works after a transmission.

The following scenario shows the problem:
	1) Open a port in RS485 mode
	2) Receive data from remote (OK)
	3) Transmit data to remote (OK)
	4) Receive data from remote (Nothing received)

In RS485 mode, imx_uart_start_tx() calls imx_uart_stop_rx() and, when the
transmission is complete, imx_uart_stop_tx() calls imx_uart_start_rx().

Since the above commit imx_uart_stop_rx() now sets the loopback bit but
imx_uart_start_rx() does not clear it causing the hardware to remain in
loopback mode and not receive external data.

Fix this by moving the existing loopback disable code to a helper function
and calling it from imx_uart_start_rx() too.

Fixes: 79d0224f6bf2 ("tty: serial: imx: Handle RS485 DE signal active high")
Cc: stable@vger.kernel.org
Signed-off-by: Martin Fuzzey <martin.fuzzey@flowbird.group>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230616104838.2729694-1-martin.fuzzey@flowbird.group
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index b2bf3cb449f4ae6f6a44db95765cf54bf35dba6e..7341d060f85cbac82c50711693be7bb4891a4f90 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -369,6 +369,16 @@ static void imx_uart_soft_reset(struct imx_port *sport)
        sport->idle_counter = 0;
 }
 
+static void imx_uart_disable_loopback_rs485(struct imx_port *sport)
+{
+       unsigned int uts;
+
+       /* See SER_RS485_ENABLED/UTS_LOOP comment in imx_uart_probe() */
+       uts = imx_uart_readl(sport, imx_uart_uts_reg(sport));
+       uts &= ~UTS_LOOP;
+       imx_uart_writel(sport, uts, imx_uart_uts_reg(sport));
+}
+
 /* called with port.lock taken and irqs off */
 static void imx_uart_start_rx(struct uart_port *port)
 {
@@ -390,6 +400,7 @@ static void imx_uart_start_rx(struct uart_port *port)
        /* Write UCR2 first as it includes RXEN */
        imx_uart_writel(sport, ucr2, UCR2);
        imx_uart_writel(sport, ucr1, UCR1);
+       imx_uart_disable_loopback_rs485(sport);
 }
 
 /* called with port.lock taken and irqs off */
@@ -1422,7 +1433,7 @@ static int imx_uart_startup(struct uart_port *port)
        int retval;
        unsigned long flags;
        int dma_is_inited = 0;
-       u32 ucr1, ucr2, ucr3, ucr4, uts;
+       u32 ucr1, ucr2, ucr3, ucr4;
 
        retval = clk_prepare_enable(sport->clk_per);
        if (retval)
@@ -1521,10 +1532,7 @@ static int imx_uart_startup(struct uart_port *port)
                imx_uart_writel(sport, ucr2, UCR2);
        }
 
-       /* See SER_RS485_ENABLED/UTS_LOOP comment in imx_uart_probe() */
-       uts = imx_uart_readl(sport, imx_uart_uts_reg(sport));
-       uts &= ~UTS_LOOP;
-       imx_uart_writel(sport, uts, imx_uart_uts_reg(sport));
+       imx_uart_disable_loopback_rs485(sport);
 
        spin_unlock_irqrestore(&sport->port.lock, flags);