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Commit 6d215f83 authored by Stefan Agner's avatar Stefan Agner Committed by Greg Kroah-Hartman
Browse files

serial: imx: warn user when using unsupported configuration 



When using half-duplex mode (which disables receiver during txing)
the RTS signal cannot be driven low during transmission when using
i.MX UART RTS/CTS control. This seems to be a limitation of the
i.MX UART IP: The RTS (CTS_B) signal is controlled by the receiver.
When the receiver is disabled, the signal stays in UART logic idle
state which is high...

If SER_RS485_RTS_ON_SEND is used, RTS needs to be high active during
transmission. Since this is the default state of the RTS (CTS_B)
signal when the receiver is off, half-duplex mode in this
configuration works fine.

However, a low-active RTS signal (flag SER_RS485_RTS_ON_SEND not set)
cannot be generated when the receiver is turned off.

Print an error if the user selects this unsupported configuration
(both SER_RS485_RTS_ON_SEND and SER_RS485_RX_DURING_TX unset) and
configure the closest working configuration (set the
SER_RS485_RX_DURING_TX flag).

Signed-off-by: default avatarStefan Agner <stefan@agner.ch>
Acked-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 46c6975a

drivers/tty/serial/imx.c

+17 −0
Original line number Diff line number Diff line
@@ -1833,6 +1833,11 @@ static int imx_uart_rs485_config(struct uart_port *port, 
		rs485conf->flags &= ~SER_RS485_ENABLED;



	if (rs485conf->flags & SER_RS485_ENABLED) {

		/* Enable receiver if low-active RTS signal is requested */

		if (sport->have_rtscts &&  !sport->have_rtsgpio &&

		    !(rs485conf->flags & SER_RS485_RTS_ON_SEND))

			rs485conf->flags |= SER_RS485_RX_DURING_TX;



		/* disable transmitter */

		ucr2 = imx_uart_readl(sport, UCR2);

		if (rs485conf->flags & SER_RS485_RTS_AFTER_SEND)
@@ -2265,6 +2270,18 @@ static int imx_uart_probe(struct platform_device *pdev) 
	    (!sport->have_rtscts && !sport->have_rtsgpio))

		dev_err(&pdev->dev, "no RTS control, disabling rs485\n");



	/*

	 * If using the i.MX UART RTS/CTS control then the RTS (CTS_B)

	 * signal cannot be set low during transmission in case the

	 * receiver is off (limitation of the i.MX UART IP).

	 */

	if (sport->port.rs485.flags & SER_RS485_ENABLED &&

	    sport->have_rtscts && !sport->have_rtsgpio &&

	    (!(sport->port.rs485.flags & SER_RS485_RTS_ON_SEND) &&

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

		dev_err(&pdev->dev,

			"low-active RTS not possible when receiver is off, enabling receiver\n");



	imx_uart_rs485_config(&sport->port, &sport->port.rs485);



	/* Disable interrupts before requesting them */