tty: imx serial: Implement support for reversing TX and RX polarity

The peripheral has support for inverting its input and/or output
signals.  This is useful if the hardware flips polarity of the
peripheral's signal, such as swapped +/- pins on an RS-422 transceiver,
or an inverting level shifter.  Add support for these control registers
via the device tree binding.

As part of this change, make the writes of the various registers more
uniform by moving the UCR3 block up near the other registers' blocks,
since the INVT bit must be set before enabling the peripheral.

Signed-off-by: George Hilliard <ghilliard@kopismobile.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20200226222319.18383-3-ghilliard@kopismobile.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index d337782b36486c86db6084c24975dbe0ffbf8bdc..f4d68109bc8bae51954ae98ac5d6bcdbfaddc189 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -195,6 +195,8 @@ struct imx_port {
        unsigned int            have_rtscts:1;
        unsigned int            have_rtsgpio:1;
        unsigned int            dte_mode:1;
+       unsigned int            inverted_tx:1;
+       unsigned int            inverted_rx:1;
        struct clk              *clk_ipg;
        struct clk              *clk_per;
        const struct imx_uart_data *devdata;
@@ -1335,7 +1337,7 @@ static int imx_uart_startup(struct uart_port *port)
        int retval, i;
        unsigned long flags;
        int dma_is_inited = 0;
-       u32 ucr1, ucr2, ucr4;
+       u32 ucr1, ucr2, ucr3, ucr4;
 
        retval = clk_prepare_enable(sport->clk_per);
        if (retval)
@@ -1387,11 +1389,29 @@ static int imx_uart_startup(struct uart_port *port)
 
        imx_uart_writel(sport, ucr1, UCR1);
 
-       ucr4 = imx_uart_readl(sport, UCR4) & ~UCR4_OREN;
+       ucr4 = imx_uart_readl(sport, UCR4) & ~(UCR4_OREN | UCR4_INVR);
        if (!sport->dma_is_enabled)
                ucr4 |= UCR4_OREN;
+       if (sport->inverted_rx)
+               ucr4 |= UCR4_INVR;
        imx_uart_writel(sport, ucr4, UCR4);
 
+       ucr3 = imx_uart_readl(sport, UCR3) & ~UCR3_INVT;
+       /*
+        * configure tx polarity before enabling tx
+        */
+       if (sport->inverted_tx)
+               ucr3 |= UCR3_INVT;
+
+       if (!imx_uart_is_imx1(sport)) {
+               ucr3 |= UCR3_DTRDEN | UCR3_RI | UCR3_DCD;
+
+               if (sport->dte_mode)
+                       /* disable broken interrupts */
+                       ucr3 &= ~(UCR3_RI | UCR3_DCD);
+       }
+       imx_uart_writel(sport, ucr3, UCR3);
+
        ucr2 = imx_uart_readl(sport, UCR2) & ~UCR2_ATEN;
        ucr2 |= (UCR2_RXEN | UCR2_TXEN);
        if (!sport->have_rtscts)
@@ -1404,20 +1424,6 @@ static int imx_uart_startup(struct uart_port *port)
                ucr2 &= ~UCR2_RTSEN;
        imx_uart_writel(sport, ucr2, UCR2);
 
-       if (!imx_uart_is_imx1(sport)) {
-               u32 ucr3;
-
-               ucr3 = imx_uart_readl(sport, UCR3);
-
-               ucr3 |= UCR3_DTRDEN | UCR3_RI | UCR3_DCD;
-
-               if (sport->dte_mode)
-                       /* disable broken interrupts */
-                       ucr3 &= ~(UCR3_RI | UCR3_DCD);
-
-               imx_uart_writel(sport, ucr3, UCR3);
-       }
-
        /*
         * Enable modem status interrupts
         */
@@ -2184,6 +2190,12 @@ static int imx_uart_probe_dt(struct imx_port *sport,
        if (of_get_property(np, "rts-gpios", NULL))
                sport->have_rtsgpio = 1;
 
+       if (of_get_property(np, "fsl,inverted-tx", NULL))
+               sport->inverted_tx = 1;
+
+       if (of_get_property(np, "fsl,inverted-rx", NULL))
+               sport->inverted_rx = 1;
+
        return 0;
 }
 #else