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Subject[PATCH 3/3] tty: serial: fsl_lpuart: Add support for RS-485
Date
Enable Vybrid's build-in support for RS-485 auto RTS for
controlling line direction of RS-485 transceiver driver.

Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
---
drivers/tty/serial/fsl_lpuart.c | 60 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 60 insertions(+)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 357f623..c553b14 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -820,6 +820,50 @@ static unsigned int lpuart32_tx_empty(struct uart_port *port)
TIOCSER_TEMT : 0;
}

+static int lpuart_config_rs485(struct uart_port *port,
+ struct serial_rs485 *rs485)
+{
+ struct lpuart_port *sport = container_of(port,
+ struct lpuart_port, port);
+ u8 modem = readb(sport->port.membase + UARTMODEM) &
+ ~(UARTMODEM_TXRTSPOL | UARTMODEM_TXRTSE);
+ writeb(modem, sport->port.membase + UARTMODEM);
+
+ if (rs485->flags & SER_RS485_ENABLED) {
+ /* Enable auto RS-485 RTS mode */
+ modem |= UARTMODEM_TXRTSE;
+
+ /*
+ * RTS needs to be logic HIGH either during transer _or_ after
+ * transfer, other variants are not supported by the hardware.
+ */
+ if (!(rs485->flags & (SER_RS485_RTS_ON_SEND |
+ SER_RS485_RTS_AFTER_SEND)))
+ rs485->flags |= SER_RS485_RTS_ON_SEND;
+
+ if (rs485->flags & SER_RS485_RTS_ON_SEND &&
+ rs485->flags & SER_RS485_RTS_AFTER_SEND)
+ rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
+
+ /*
+ * The hardware defaults to RTS logic HIGH while transfer.
+ * Switch polarity in case RTS shall be logic HIGH
+ * after transfer.
+ * Note: UART is assumed to be active high.
+ */
+ if (rs485->flags & SER_RS485_RTS_ON_SEND)
+ modem &= ~UARTMODEM_TXRTSPOL;
+ else if (rs485->flags & SER_RS485_RTS_AFTER_SEND)
+ modem |= UARTMODEM_TXRTSPOL;
+ }
+
+ /* Store the new configuration */
+ sport->port.rs485 = *rs485;
+
+ writeb(modem, sport->port.membase + UARTMODEM);
+ return 0;
+}
+
static unsigned int lpuart_get_mctrl(struct uart_port *port)
{
return TIOCM_CAR | TIOCM_CTS | TIOCM_DSR;
@@ -1204,6 +1248,12 @@ lpuart_set_termios(struct uart_port *port, struct ktermios *termios,
cr1 |= UARTCR1_M;
}

+ /* When auto RS-485 RTS mode is enabled,
+ * hardware flow control need to be disabled.
+ */
+ if (sport->port.rs485.flags & SER_RS485_ENABLED)
+ termios->c_cflag &= ~CRTSCTS;
+
if (termios->c_cflag & CRTSCTS) {
modem |= (UARTMODEM_RXRTSE | UARTMODEM_TXCTSE);
} else {
@@ -1762,6 +1812,8 @@ static int lpuart_probe(struct platform_device *pdev)
sport->port.ops = &lpuart_pops;
sport->port.flags = UPF_BOOT_AUTOCONF;

+ sport->port.rs485_config = lpuart_config_rs485;
+
sport->clk = devm_clk_get(&pdev->dev, "ipg");
if (IS_ERR(sport->clk)) {
ret = PTR_ERR(sport->clk);
@@ -1802,6 +1854,14 @@ static int lpuart_probe(struct platform_device *pdev)
dev_info(sport->port.dev, "DMA rx channel request failed, "
"operating without rx DMA\n");

+ if (of_property_read_bool(np, "linux,rs485-enabled-at-boot-time")) {
+ sport->port.rs485.flags |= SER_RS485_ENABLED;
+ sport->port.rs485.flags |= SER_RS485_RTS_ON_SEND;
+ writeb(UARTMODEM_TXRTSE, sport->port.membase + UARTMODEM);
+ } else {
+ sport->port.rs485.flags &= ~SER_RS485_ENABLED;
+ }
+
return 0;
}

--
2.1.0


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