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serial: ar933x_uart: add RS485 support
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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>
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Daniel Golle authored and Greg Kroah-Hartman committed Mar 6, 2020
1 parent 9fa3c4b commit 9be1064
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Showing 2 changed files with 108 additions and 6 deletions.
1 change: 1 addition & 0 deletions drivers/tty/serial/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
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113 changes: 107 additions & 6 deletions drivers/tty/serial/ar933x_uart.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand All @@ -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
Expand All @@ -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,
Expand Down Expand 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;
Expand All @@ -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)
Expand All @@ -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 =
Expand All @@ -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)
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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];
Expand Down Expand Up @@ -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;
Expand All @@ -690,13 +778,26 @@ 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);

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
Expand Down

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