Commit 1a613626 authored by Fabio Estevam's avatar Fabio Estevam Committed by Greg Kroah-Hartman
Browse files

serial: imx: Fix the RTS GPIO polarity in RS485 mode 



On a board that needs to drive RTS GPIO high in order to enable the
transmission of a RS485 transceiver the following description is
passed in the devide tree:

&uart4 {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_uart4>;
        rts-gpios = <&gpio6 2 GPIO_ACTIVE_HIGH>;
        status = "okay";
};

and userspace configures the uart port as follows:

/* enable RS485 mode: */
rs485conf.flags |= SER_RS485_ENABLED;

/* set logical level for RTS pin equal to 1 when sending: */
rs485conf.flags |= SER_RS485_RTS_ON_SEND;

/* set logical level for RTS pin equal to 0 after sending: */
rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND);

However the RTS GPIO polarity observed in the oscilloscope is inverted.

When the SER_RS485_RTS_ON_SEND flag is set the imx_port_rts_active()
function should be called and following the same logic when
SER_RS485_RTS_AFTER_SEND flag is cleared the imx_port_rts_inactive()
should be called.

Do such logic change so that RS485 communication in half duplex can
work successfully when the RTS GPIO pin is passed via device tree.

Signed-off-by: default avatarFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent aa42db44

drivers/tty/serial/imx.c

+10 −10
Original line number Diff line number Diff line
@@ -377,9 +377,9 @@ static void imx_stop_tx(struct uart_port *port) 
	    readl(port->membase + USR2) & USR2_TXDC) {

		temp = readl(port->membase + UCR2);

		if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)

			imx_port_rts_inactive(sport, &temp);

		else

			imx_port_rts_active(sport, &temp);

		else

			imx_port_rts_inactive(sport, &temp);

		temp |= UCR2_RXEN;

		writel(temp, port->membase + UCR2);
@@ -585,9 +585,9 @@ static void imx_start_tx(struct uart_port *port) 
	if (port->rs485.flags & SER_RS485_ENABLED) {

		temp = readl(port->membase + UCR2);

		if (port->rs485.flags & SER_RS485_RTS_ON_SEND)

			imx_port_rts_inactive(sport, &temp);

		else

			imx_port_rts_active(sport, &temp);

		else

			imx_port_rts_inactive(sport, &temp);

		if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))

			temp &= ~UCR2_RXEN;

		writel(temp, port->membase + UCR2);
@@ -1477,9 +1477,9 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios, 
				 */

				if (port->rs485.flags &

				    SER_RS485_RTS_AFTER_SEND)

					imx_port_rts_inactive(sport, &ucr2);

				else

					imx_port_rts_active(sport, &ucr2);

				else

					imx_port_rts_inactive(sport, &ucr2);

			} else {

				imx_port_rts_auto(sport, &ucr2);

			}
@@ -1489,9 +1489,9 @@ imx_set_termios(struct uart_port *port, struct ktermios *termios, 
	} else if (port->rs485.flags & SER_RS485_ENABLED) {

		/* disable transmitter */

		if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)

			imx_port_rts_inactive(sport, &ucr2);

		else

			imx_port_rts_active(sport, &ucr2);

		else

			imx_port_rts_inactive(sport, &ucr2);

	}
@@ -1733,9 +1733,9 @@ static int imx_rs485_config(struct uart_port *port, 
		/* disable transmitter */

		temp = readl(sport->port.membase + UCR2);

		if (rs485conf->flags & SER_RS485_RTS_AFTER_SEND)

			imx_port_rts_inactive(sport, &temp);

		else

			imx_port_rts_active(sport, &temp);

		else

			imx_port_rts_inactive(sport, &temp);

		writel(temp, sport->port.membase + UCR2);

	}

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