[PATCH v3 2/2] tty: imx serial: Implement support for reversing TX and RX polarity

[George Hilliard <ghilliard@kopismobile.com>]

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.

Signed-off-by: George Hilliard <ghilliard@kopismobile.com>
---
v1..v2: Remove confidentiality spam
v2..v3: Set *and* clear register, and do it before TX enable

 drivers/tty/serial/imx.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 0c6c63166250..205627bcad66 100644
--- 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)
@@ -1390,8 +1392,22 @@ static int imx_uart_startup(struct uart_port *port)
 	ucr4 = imx_uart_readl(sport, UCR4) & ~UCR4_OREN;
 	if (!sport->dma_is_enabled)
 		ucr4 |= UCR4_OREN;
+	if (sport->inverted_rx)
+		ucr4 |= UCR4_INVR;
+	else
+		ucr4 &= ~UCR4_INVR;
 	imx_uart_writel(sport, ucr4, UCR4);
 
+	/*
+	 * configure tx polarity before enabling tx
+	 */
+	ucr3 = imx_uart_readl(sport, UCR3);
+	if (sport->inverted_tx)
+		ucr3 |= UCR3_INVT;
+	else
+		ucr3 &= ~UCR3_INVT;
+	imx_uart_writel(sport, ucr3, UCR3);
+
 	ucr2 = imx_uart_readl(sport, UCR2) & ~UCR2_ATEN;
 	ucr2 |= (UCR2_RXEN | UCR2_TXEN);
 	if (!sport->have_rtscts)
@@ -1405,10 +1421,6 @@ static int imx_uart_startup(struct uart_port *port)
 	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)
@@ -2184,6 +2196,12 @@ 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
-- 
2.25.0