serial: imx: warn user when using unsupported configuration (6d215f83) · Commits · 戴 / test

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:

Stefan Agner <stefan@agner.ch> Acked-by:

Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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 */

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