tty: serial: fsl_lpuart: Add support for RS-485

Enable Vybrid's build-in support for RS-485 auto RTS for controlling line
direction of RS-485 transceiver driver.

Enable RS485 feature by either using ioctrl 'TIOCSRS485' or enable it in the
device tree by setting 'linux,rs485-enabled-at-boot-time' property.

Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 6ab4b25..93f172e 100644 (file)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -917,6 +917,52 @@ static void lpuart_dma_rx_free(struct uart_port *port)
        sport->dma_rx_cookie = -EINVAL;
 }
 
+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)
 {
        unsigned int temp = 0;
@@ -950,17 +996,22 @@ static unsigned int lpuart32_get_mctrl(struct uart_port *port)
 static void lpuart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 {
        unsigned char temp;
+       struct lpuart_port *sport = container_of(port,
+                               struct lpuart_port, port);
 
-       temp = readb(port->membase + UARTMODEM) &
+       /* Make sure RXRTSE bit is not set when RS485 is enabled */
+       if (!(sport->port.rs485.flags & SER_RS485_ENABLED)) {
+               temp = readb(sport->port.membase + UARTMODEM) &
                        ~(UARTMODEM_RXRTSE | UARTMODEM_TXCTSE);
 
-       if (mctrl & TIOCM_RTS)
-               temp |= UARTMODEM_RXRTSE;
+               if (mctrl & TIOCM_RTS)
+                       temp |= UARTMODEM_RXRTSE;
 
-       if (mctrl & TIOCM_CTS)
-               temp |= UARTMODEM_TXCTSE;
+               if (mctrl & TIOCM_CTS)
+                       temp |= UARTMODEM_TXCTSE;
 
-       writeb(temp, port->membase + UARTMODEM);
+               writeb(temp, port->membase + UARTMODEM);
+       }
 }
 
 static void lpuart32_set_mctrl(struct uart_port *port, unsigned int mctrl)
@@ -1256,6 +1307,13 @@ 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 {
@@ -1870,6 +1928,8 @@ 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);
@@ -1910,6 +1970,12 @@ 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);
+       }
+
        return 0;
 }