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RCVD_TLS_ALL(0.00)[]; ASN(0.00)[asn:13030, ipnet:2001:1620::/32, country:CH]; RCVD_COUNT_ZERO(0.00)[0]; FROM_HAS_DN(0.00)[]; MID_CONTAINS_FROM(1.00)[]; TO_DN_SOME(0.00)[]; MIME_GOOD(-0.10)[text/plain]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; BAYES_HAM(-2.96)[99.85%]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[]; RCPT_COUNT_SEVEN(0.00)[7] Sender: linux-serial-owner@vger.kernel.org X-Mailing-List: linux-serial@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: When using half-duplex mode (which disables receiver during txing) the RTS signal cannot be driven low during transmission. 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 --- drivers/tty/serial/imx.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index 91f3a1a5cb7f..1ba7e98ddc76 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -1833,6 +1833,10 @@ 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 (rs485conf->flags & SER_RS485_RTS_AFTER_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 +2269,17 @@ 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"); + /* + * 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->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 */ -- 2.17.0