[PATCH 2/2] tty: serial: uartps: Add rs485 support to uartps driver

Manikanta Guntupalli
2023-04-26T12:31:24Z

Add rs485 half duplex mode support to uartps driver by making GPIO
high before tx and low before rx.

Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@amd.com>
---
drivers/tty/serial/xilinx_uartps.c | 96 +++++++++++++++++++++++++++++-
1 file changed, 95 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 8e521c69a959..339b962460ee 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -23,6 +23,8 @@
#include <linux/module.h>
#include <linux/pm_runtime.h>
#include <linux/iopoll.h>
+#include <linux/gpio.h>
+#include <linux/gpio/consumer.h>

#define CDNS_UART_TTY_NAME "ttyPS"
#define CDNS_UART_NAME "xuartps"
@@ -193,6 +195,7 @@ MODULE_PARM_DESC(rx_timeout, "Rx timeout, 1-255");
* @clk_rate_change_nb: Notifier block for clock changes
* @quirks: Flags for RXBS support.
* @cts_override: Modem control state override
+ * @gpiod: Pointer to the gpio descriptor
*/
struct cdns_uart {
struct uart_port *port;
@@ -203,10 +206,16 @@ struct cdns_uart {
struct notifier_block clk_rate_change_nb;
u32 quirks;
bool cts_override;
+ struct gpio_desc *gpiod;
};
struct cdns_platform_data {
u32 quirks;
};
+
+struct serial_rs485 cdns_rs485_supported = {
+ .flags = SER_RS485_ENABLED,
+};
+
#define to_cdns_uart(_nb) container_of(_nb, struct cdns_uart, \
clk_rate_change_nb)

@@ -305,6 +314,27 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus)
tty_flip_buffer_push(&port->state->port);
}

+/**
+ * cdns_rs485_tx_setup - Tx setup specific to rs485
+ * @cdns_uart: Handle to the cdns_uart
+ */
+static void cdns_rs485_tx_setup(struct cdns_uart *cdns_uart)
+{
+ gpiod_set_value(cdns_uart->gpiod, 1);
+}
+
+/**
+ * cdns_rs485_rx_setup - Rx setup specific to rs485
+ * @cdns_uart: Handle to the cdns_uart
+ */
+
+static void cdns_rs485_rx_setup(struct cdns_uart *cdns_uart)
+{
+ gpiod_set_value(cdns_uart->gpiod, 0);
+}
+
+static unsigned int cdns_uart_tx_empty(struct uart_port *port);
+
/**
* cdns_uart_handle_tx - Handle the bytes to be Txed.
* @dev_id: Id of the UART port
@@ -313,12 +343,17 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus)
static void cdns_uart_handle_tx(void *dev_id)
{
struct uart_port *port = (struct uart_port *)dev_id;
+ struct cdns_uart *cdns_uart = port->private_data;
struct circ_buf *xmit = &port->state->xmit;
+ unsigned long time_out;
unsigned int numbytes;

+ if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED)
+ cdns_rs485_tx_setup(cdns_uart);
+
if (uart_circ_empty(xmit)) {
writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_IDR);
- return;
+ goto rs485_rx_setup;
}

numbytes = port->fifosize;
@@ -332,6 +367,21 @@ static void cdns_uart_handle_tx(void *dev_id)

if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
uart_write_wakeup(port);
+
+rs485_rx_setup:
+ if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED) {
+ time_out = jiffies + usecs_to_jiffies(TX_TIMEOUT);
+ /* Wait for tx completion */
+ while ((cdns_uart_tx_empty(cdns_uart->port) != TIOCSER_TEMT) &&
+ time_before(jiffies, time_out))
+ cpu_relax();
+
+ /*
+ * Default Rx should be setup, because RX signaling path
+ * need to enable to receive data.
+ */
+ cdns_rs485_rx_setup(cdns_uart);
+ }
}

/**
@@ -829,6 +879,9 @@ static int cdns_uart_startup(struct uart_port *port)
(CDNS_UART_CR_TXRST | CDNS_UART_CR_RXRST))
cpu_relax();

+ if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED)
+ cdns_rs485_rx_setup(cdns_uart);
+
/*
* Clear the RX disable bit and then set the RX enable bit to enable
* the receiver.
@@ -1455,6 +1508,25 @@ MODULE_DEVICE_TABLE(of, cdns_uart_of_match);
/* Temporary variable for storing number of instances */
static int instances;

+/**
+ * cdns_rs485_config - Called when an application calls TIOCSRS485 ioctl.
+ * @port: Pointer to the uart_port structure
+ * @termios: Pointer to the ktermios structure
+ * @rs485: Pointer to the serial_rs485 structure
+ *
+ * Return: 0
+ */
+static int cdns_rs485_config(struct uart_port *port, struct ktermios *termios,
+ struct serial_rs485 *rs485)
+{
+ port->rs485 = *rs485;
+
+ if (rs485->flags & SER_RS485_ENABLED)
+ dev_dbg(port->dev, "Setting UART to RS485\n");
+
+ return 0;
+}
+
/**
* cdns_uart_probe - Platform driver probe
* @pdev: Pointer to the platform device structure
@@ -1597,9 +1669,30 @@ static int cdns_uart_probe(struct platform_device *pdev)
port->private_data = cdns_uart_data;
port->read_status_mask = CDNS_UART_IXR_TXEMPTY | CDNS_UART_IXR_RXTRIG |
CDNS_UART_IXR_OVERRUN | CDNS_UART_IXR_TOUT;
+ port->rs485_config = cdns_rs485_config;
+ port->rs485_supported = cdns_rs485_supported;
cdns_uart_data->port = port;
platform_set_drvdata(pdev, port);

+ rc = uart_get_rs485_mode(port);
+
+ if (rc)
+ goto err_out_clk_notifier;
+
+ cdns_uart_data->gpiod = devm_gpiod_get_optional(&pdev->dev, "txrx",
+ GPIOD_OUT_LOW);
+
+ if (IS_ERR(cdns_uart_data->gpiod)) {
+ rc = PTR_ERR(cdns_uart_data->gpiod);
+ dev_err(port->dev, "xuartps: devm_gpiod_get_optional failed\n");
+ goto err_out_clk_notifier;
+ }
+
+ if (cdns_uart_data->gpiod) {
+ gpiod_direction_output(cdns_uart_data->gpiod, GPIOD_OUT_LOW);
+ gpiod_set_value(cdns_uart_data->gpiod, 0);
+ }
+
pm_runtime_use_autosuspend(&pdev->dev);
pm_runtime_set_autosuspend_delay(&pdev->dev, UART_AUTOSUSPEND_TIMEOUT);
pm_runtime_set_active(&pdev->dev);
@@ -1646,6 +1739,7 @@ static int cdns_uart_probe(struct platform_device *pdev)
pm_runtime_disable(&pdev->dev);
pm_runtime_set_suspended(&pdev->dev);
pm_runtime_dont_use_autosuspend(&pdev->dev);
+err_out_clk_notifier:
#ifdef CONFIG_COMMON_CLK
clk_notifier_unregister(cdns_uart_data->uartclk,
&cdns_uart_data->clk_rate_change_nb);
--
2.25.1