From 6d215f83e5fccb3dd023e97fef1bd0029bfedde9 Mon Sep 17 00:00:00 2001 From: Stefan Agner Date: Thu, 19 Apr 2018 17:39:16 +0200 Subject: [PATCH] serial: imx: warn user when using unsupported configuration MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Acked-by: Uwe Kleine-König Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/imx.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index 91f3a1a5cb7f..65d7a2bfb6d2 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -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 */ -- 2.45.2