serial: ar933x_uart: add RS485 support

Emulate half-duplex operation and use mctrl_gpio to add support for
RS485 tranceiver with transmit/receive switch hooked to RTS GPIO line.
This is needed to make use of the RS485 port found on Teltonika RUT955.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/20200221212331.GA21467@makrotopia.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 880b962015302dcae50f00d257fc25c4beaf281b..e71af33f8d8094904298858aae820395c7302889 100644 (file)
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1269,6 +1269,7 @@ config SERIAL_AR933X
        tristate "AR933X serial port support"
        depends on HAVE_CLK && ATH79
        select SERIAL_CORE
+       select SERIAL_MCTRL_GPIO if GPIOLIB
        help
          If you have an Atheros AR933X SOC based board and want to use the
          built-in UART of the SoC, say Y to this option.

diff --git a/drivers/tty/serial/ar933x_uart.c b/drivers/tty/serial/ar933x_uart.c
index ea12f10610b64dd46062735fc4e682213c407167..7e7f1398019f4722c63f2109a0ee60dc3f5435a0 100644 (file)
--- a/drivers/tty/serial/ar933x_uart.c
+++ b/drivers/tty/serial/ar933x_uart.c
@@ -13,6 +13,7 @@
 #include <linux/console.h>
 #include <linux/sysrq.h>
 #include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/platform_device.h>
 #include <linux/of.h>
 #include <linux/of_platform.h>
@@ -29,6 +30,8 @@
 
 #include <asm/mach-ath79/ar933x_uart.h>
 
+#include "serial_mctrl_gpio.h"
+
 #define DRIVER_NAME "ar933x-uart"
 
 #define AR933X_UART_MAX_SCALE  0xff
@@ -47,6 +50,8 @@ struct ar933x_uart_port {
        unsigned int            min_baud;
        unsigned int            max_baud;
        struct clk              *clk;
+       struct mctrl_gpios      *gpios;
+       struct gpio_desc        *rts_gpiod;
 };
 
 static inline unsigned int ar933x_uart_read(struct ar933x_uart_port *up,
@@ -100,6 +105,18 @@ static inline void ar933x_uart_stop_tx_interrupt(struct ar933x_uart_port *up)
        ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
 }
 
+static inline void ar933x_uart_start_rx_interrupt(struct ar933x_uart_port *up)
+{
+       up->ier |= AR933X_UART_INT_RX_VALID;
+       ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+}
+
+static inline void ar933x_uart_stop_rx_interrupt(struct ar933x_uart_port *up)
+{
+       up->ier &= ~AR933X_UART_INT_RX_VALID;
+       ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+}
+
 static inline void ar933x_uart_putc(struct ar933x_uart_port *up, int ch)
 {
        unsigned int rdata;
@@ -125,11 +142,21 @@ static unsigned int ar933x_uart_tx_empty(struct uart_port *port)
 
 static unsigned int ar933x_uart_get_mctrl(struct uart_port *port)
 {
-       return TIOCM_CAR;
+       struct ar933x_uart_port *up =
+               container_of(port, struct ar933x_uart_port, port);
+       int ret = TIOCM_CTS | TIOCM_DSR | TIOCM_CAR;
+
+       mctrl_gpio_get(up->gpios, &ret);
+
+       return ret;
 }
 
 static void ar933x_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 {
+       struct ar933x_uart_port *up =
+               container_of(port, struct ar933x_uart_port, port);
+
+       mctrl_gpio_set(up->gpios, mctrl);
 }
 
 static void ar933x_uart_start_tx(struct uart_port *port)
@@ -140,6 +167,37 @@ static void ar933x_uart_start_tx(struct uart_port *port)
        ar933x_uart_start_tx_interrupt(up);
 }
 
+static void ar933x_uart_wait_tx_complete(struct ar933x_uart_port *up)
+{
+       unsigned int status;
+       unsigned int timeout = 60000;
+
+       /* Wait up to 60ms for the character(s) to be sent. */
+       do {
+               status = ar933x_uart_read(up, AR933X_UART_CS_REG);
+               if (--timeout == 0)
+                       break;
+               udelay(1);
+       } while (status & AR933X_UART_CS_TX_BUSY);
+
+       if (timeout == 0)
+               dev_err(up->port.dev, "waiting for TX timed out\n");
+}
+
+static void ar933x_uart_rx_flush(struct ar933x_uart_port *up)
+{
+       unsigned int status;
+
+       /* clear RX_VALID interrupt */
+       ar933x_uart_write(up, AR933X_UART_INT_REG, AR933X_UART_INT_RX_VALID);
+
+       /* remove characters from the RX FIFO */
+       do {
+               ar933x_uart_write(up, AR933X_UART_DATA_REG, AR933X_UART_DATA_RX_CSR);
+               status = ar933x_uart_read(up, AR933X_UART_DATA_REG);
+       } while (status & AR933X_UART_DATA_RX_CSR);
+}
+
 static void ar933x_uart_stop_tx(struct uart_port *port)
 {
        struct ar933x_uart_port *up =
@@ -153,8 +211,7 @@ static void ar933x_uart_stop_rx(struct uart_port *port)
        struct ar933x_uart_port *up =
                container_of(port, struct ar933x_uart_port, port);
 
-       up->ier &= ~AR933X_UART_INT_RX_VALID;
-       ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+       ar933x_uart_stop_rx_interrupt(up);
 }
 
 static void ar933x_uart_break_ctl(struct uart_port *port, int break_state)
@@ -336,11 +393,20 @@ static void ar933x_uart_rx_chars(struct ar933x_uart_port *up)
 static void ar933x_uart_tx_chars(struct ar933x_uart_port *up)
 {
        struct circ_buf *xmit = &up->port.state->xmit;
+       struct serial_rs485 *rs485conf = &up->port.rs485;
        int count;
+       bool half_duplex_send = false;
 
        if (uart_tx_stopped(&up->port))
                return;
 
+       if ((rs485conf->flags & SER_RS485_ENABLED) &&
+           (up->port.x_char || !uart_circ_empty(xmit))) {
+               ar933x_uart_stop_rx_interrupt(up);
+               gpiod_set_value(up->rts_gpiod, !!(rs485conf->flags & SER_RS485_RTS_ON_SEND));
+               half_duplex_send = true;
+       }
+
        count = up->port.fifosize;
        do {
                unsigned int rdata;
@@ -368,8 +434,14 @@ static void ar933x_uart_tx_chars(struct ar933x_uart_port *up)
        if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                uart_write_wakeup(&up->port);
 
-       if (!uart_circ_empty(xmit))
+       if (!uart_circ_empty(xmit)) {
                ar933x_uart_start_tx_interrupt(up);
+       } else if (half_duplex_send) {
+               ar933x_uart_wait_tx_complete(up);
+               ar933x_uart_rx_flush(up);
+               ar933x_uart_start_rx_interrupt(up);
+               gpiod_set_value(up->rts_gpiod, !!(rs485conf->flags & SER_RS485_RTS_AFTER_SEND));
+       }
 }
 
 static irqreturn_t ar933x_uart_interrupt(int irq, void *dev_id)
@@ -427,8 +499,7 @@ static int ar933x_uart_startup(struct uart_port *port)
                AR933X_UART_CS_TX_READY_ORIDE | AR933X_UART_CS_RX_READY_ORIDE);
 
        /* Enable RX interrupts */
-       up->ier = AR933X_UART_INT_RX_VALID;
-       ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+       ar933x_uart_start_rx_interrupt(up);
 
        spin_unlock_irqrestore(&up->port.lock, flags);
 
@@ -511,6 +582,21 @@ static const struct uart_ops ar933x_uart_ops = {
        .verify_port    = ar933x_uart_verify_port,
 };
 
+static int ar933x_config_rs485(struct uart_port *port,
+                               struct serial_rs485 *rs485conf)
+{
+       struct ar933x_uart_port *up =
+               container_of(port, struct ar933x_uart_port, port);
+
+       if ((rs485conf->flags & SER_RS485_ENABLED) &&
+           !up->rts_gpiod) {
+               dev_err(port->dev, "RS485 needs rts-gpio\n");
+               return 1;
+       }
+       port->rs485 = *rs485conf;
+       return 0;
+}
+
 #ifdef CONFIG_SERIAL_AR933X_CONSOLE
 static struct ar933x_uart_port *
 ar933x_console_ports[CONFIG_SERIAL_AR933X_NR_UARTS];
@@ -680,6 +766,8 @@ static int ar933x_uart_probe(struct platform_device *pdev)
                goto err_disable_clk;
        }
 
+       uart_get_rs485_mode(&pdev->dev, &port->rs485);
+
        port->mapbase = mem_res->start;
        port->line = id;
        port->irq = irq_res->start;
@@ -690,6 +778,7 @@ static int ar933x_uart_probe(struct platform_device *pdev)
        port->regshift = 2;
        port->fifosize = AR933X_UART_FIFO_SIZE;
        port->ops = &ar933x_uart_ops;
+       port->rs485_config = ar933x_config_rs485;
 
        baud = ar933x_uart_get_baud(port->uartclk, AR933X_UART_MAX_SCALE, 1);
        up->min_baud = max_t(unsigned int, baud, AR933X_UART_MIN_BAUD);
@@ -697,6 +786,18 @@ static int ar933x_uart_probe(struct platform_device *pdev)
        baud = ar933x_uart_get_baud(port->uartclk, 0, AR933X_UART_MAX_STEP);
        up->max_baud = min_t(unsigned int, baud, AR933X_UART_MAX_BAUD);
 
+       up->gpios = mctrl_gpio_init(port, 0);
+       if (IS_ERR(up->gpios) && PTR_ERR(up->gpios) != -ENOSYS)
+               return PTR_ERR(up->gpios);
+
+       up->rts_gpiod = mctrl_gpio_to_gpiod(up->gpios, UART_GPIO_RTS);
+
+       if ((port->rs485.flags & SER_RS485_ENABLED) &&
+           !up->rts_gpiod) {
+               dev_err(&pdev->dev, "lacking rts-gpio, disabling RS485\n");
+               port->rs485.flags &= ~SER_RS485_ENABLED;
+       }
+
 #ifdef CONFIG_SERIAL_AR933X_CONSOLE
        ar933x_console_ports[up->port.line] = up;
 #endif