[v4,2/2] tty: imx serial: Implement support for reversing TX and RX polarity

Message ID 20200226222319.18383-3-ghilliard@kopismobile.com
State New
Headers show
Series
  • Implement support for inverted serial TX/RX on i.MX
Related show

Commit Message

George Hilliard Feb. 26, 2020, 10:23 p.m.
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>
---
v1..v2: Remove confidentiality spam
v2..v3: Set *and* clear register, and do it before TX enable
v3..v4: Clean up bit manipulation; move UCR3 block so it's written once

 drivers/tty/serial/imx.c | 44 +++++++++++++++++++++++++---------------
 1 file changed, 28 insertions(+), 16 deletions(-)

Patch

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 0c6c63166250..81a981849a4b 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)
@@ -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