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From:   Manikanta Guntupalli <manikanta.guntupalli@amd.com>
To:     <git@amd.com>, <michal.simek@amd.com>,
        <gregkh@linuxfoundation.org>, <robh+dt@kernel.org>,
        <krzysztof.kozlowski+dt@linaro.org>, <conor+dt@kernel.org>,
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        <linux-kernel@vger.kernel.org>, <jirislaby@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
CC:     <radhey.shyam.pandey@amd.com>, <srinivas.goud@amd.com>,
        <shubhrajyoti.datta@amd.com>, <manion05gk@gmail.com>,
        Manikanta Guntupalli <manikanta.guntupalli@amd.com>
Subject: [PATCH V4 3/3] tty: serial: uartps: Add rs485 support to uartps driver
Date:   Mon, 11 Dec 2023 14:41:59 +0530
Message-ID: <20231211091159.58564-4-manikanta.guntupalli@amd.com>
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Add rs485 support to uartps driver. Use either rts-gpios or RTS
to control RS485 phy as driver or a receiver.

Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@amd.com>
---
Changes for V2:
Modify optional gpio name to xlnx,phy-ctrl-gpios.
Update commit description.
Add support for RTS, delay_rts_before_send and delay_rts_after_send in RS485 mode.

Changes for V3:
Modify optional gpio name to rts-gpios.
Update commit description.
Move cdns_uart_tx_empty function to avoid prototype statement.
Remove assignment of struct serial_rs485 to port->rs485 as
serial core performs that.
Switch to native RTS in non GPIO case.
Handle rs485 during stop tx.
Remove explicit calls to configure gpio direction and value,
as devm_gpiod_get_optional performs that by using GPIOD_OUT_LOW argument.
Update implementation to support configuration of GPIO/RTS value
based on user configuration of SER_RS485_RTS_ON_SEND and
SER_RS485_RTS_AFTER_SEND. Move implementation to start_tx from handle_tx.

Changes for V4:
Create separate patch for cdns_uart_tx_empty relocation.
Call cdns_rs485_rx_setup() before uart_add_one_port() in probe.
Update gpio descriptor name to gpiod_rts.
Instead of cdns_rs485_config_gpio_rts_high() and
cdns_rs485_config_gpio_rts_low() functions for RTS/GPIO value
configuration implement cdns_rts_gpio_enable().
Disable auto rts and call cdns_uart_stop_tx() from cdns_rs485_config.
Use timer instead of mdelay for delay_rts_before_send and delay_rts_after_send.
Update cdns_uart_set_mctrl to support GPIO/RTS.
---
 drivers/tty/serial/xilinx_uartps.c | 214 +++++++++++++++++++++++++++--
 1 file changed, 205 insertions(+), 9 deletions(-)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index f7fc2de8778d..e7f2c43fabd3 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -22,7 +22,9 @@
 #include <linux/of.h>
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
-#include <linux/iopoll.h>
+#include <linux/gpio.h>
+#include <linux/gpio/consumer.h>
+#include <linux/delay.h>
 
 #define CDNS_UART_TTY_NAME	"ttyPS"
 #define CDNS_UART_NAME		"xuartps"
@@ -193,6 +195,10 @@ 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_rts:		Pointer to the gpio descriptor
+ * @rs485_tx_started:	RS485 tx state
+ * @timer:		Timer for tx and rx
+ * @stop_tx_timer:	Timer for stop tx
  */
 struct cdns_uart {
 	struct uart_port	*port;
@@ -203,10 +209,22 @@ struct cdns_uart {
 	struct notifier_block	clk_rate_change_nb;
 	u32			quirks;
 	bool cts_override;
+	struct gpio_desc	*gpiod_rts;
+	bool			rs485_tx_started;
+	struct timer_list	timer;
+	struct timer_list	stop_tx_timer;
 };
 struct cdns_platform_data {
 	u32 quirks;
 };
+
+struct serial_rs485 cdns_rs485_supported = {
+	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND |
+		 SER_RS485_RTS_AFTER_SEND,
+	.delay_rts_before_send = 1,
+	.delay_rts_after_send = 1,
+};
+
 #define to_cdns_uart(_nb) container_of(_nb, struct cdns_uart, \
 		clk_rate_change_nb)
 
@@ -305,6 +323,55 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus)
 	tty_flip_buffer_push(&port->state->port);
 }
 
+/**
+ * cdns_rts_gpio_enable - Configure RTS/GPIO to high/low
+ * @cdns_uart: Handle to the cdns_uart
+ * @enable: Value to be set to RTS/GPIO
+ */
+static void cdns_rts_gpio_enable(struct cdns_uart *cdns_uart, bool enable)
+{
+	u32 val;
+
+	if (cdns_uart->gpiod_rts) {
+		gpiod_set_value(cdns_uart->gpiod_rts, enable);
+	} else {
+		val = readl(cdns_uart->port->membase + CDNS_UART_MODEMCR);
+		if (enable)
+			val &= ~CDNS_UART_MODEMCR_RTS;
+		else
+			val |= CDNS_UART_MODEMCR_RTS;
+		writel(val, cdns_uart->port->membase + CDNS_UART_MODEMCR);
+	}
+}
+
+/**
+ * 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)
+{
+	if (cdns_uart->port->rs485.flags & SER_RS485_RTS_ON_SEND)
+		cdns_rts_gpio_enable(cdns_uart, 1);
+	else
+		cdns_rts_gpio_enable(cdns_uart, 0);
+
+	cdns_uart->rs485_tx_started = true;
+}
+
+/**
+ * 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)
+{
+	if (cdns_uart->port->rs485.flags & SER_RS485_RTS_AFTER_SEND)
+		cdns_rts_gpio_enable(cdns_uart, 1);
+	else
+		cdns_rts_gpio_enable(cdns_uart, 0);
+
+	cdns_uart->rs485_tx_started = false;
+}
+
 /**
  * cdns_uart_tx_empty -  Check whether TX is empty
  * @port: Handle to the uart port structure
@@ -579,6 +646,42 @@ static int cdns_uart_clk_notifier_cb(struct notifier_block *nb,
 }
 #endif
 
+/**
+ * cdns_rs485_rx_callback - Timer rx callback handler for rs485.
+ * @t: Handle to the timer list structure
+ */
+static void cdns_rs485_rx_callback(struct timer_list *t)
+{
+	struct cdns_uart *cdns_uart = from_timer(cdns_uart, t, timer);
+
+	/*
+	 * Default Rx should be setup, because Rx signaling path
+	 * need to enable to receive data.
+	 */
+	cdns_rs485_rx_setup(cdns_uart);
+}
+
+/**
+ * cdns_rs485_tx_callback - Timer tx callback handler for rs485.
+ * @t: Handle to the timer list structure
+ */
+static void cdns_rs485_tx_callback(struct timer_list *t)
+{
+	struct cdns_uart *cdns_uart = from_timer(cdns_uart, t, timer);
+
+	cdns_uart_handle_tx(cdns_uart->port);
+
+	/* Enable the TX Empty interrupt */
+	writel(CDNS_UART_IXR_TXEMPTY, cdns_uart->port->membase + CDNS_UART_IER);
+
+	if (uart_circ_empty(&cdns_uart->port->state->xmit) ||
+	    uart_tx_stopped(cdns_uart->port)) {
+		timer_setup(&cdns_uart->timer, cdns_rs485_rx_callback, 0);
+		mod_timer(&cdns_uart->timer, jiffies +
+			  msecs_to_jiffies(cdns_uart->port->rs485.delay_rts_after_send));
+	}
+}
+
 /**
  * cdns_uart_start_tx -  Start transmitting bytes
  * @port: Handle to the uart port structure
@@ -586,6 +689,7 @@ static int cdns_uart_clk_notifier_cb(struct notifier_block *nb,
 static void cdns_uart_start_tx(struct uart_port *port)
 {
 	unsigned int status;
+	struct cdns_uart *cdns_uart = port->private_data;
 
 	if (uart_tx_stopped(port))
 		return;
@@ -604,10 +708,40 @@ static void cdns_uart_start_tx(struct uart_port *port)
 
 	writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_ISR);
 
-	cdns_uart_handle_tx(port);
+	if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED) {
+		if (!cdns_uart->rs485_tx_started) {
+			timer_setup(&cdns_uart->timer,
+				    cdns_rs485_tx_callback, 0);
+			cdns_rs485_tx_setup(cdns_uart);
+			mod_timer(&cdns_uart->timer, jiffies +
+				  msecs_to_jiffies(port->rs485.delay_rts_before_send));
+		} else {
+			if (!timer_pending(&cdns_uart->timer))
+				mod_timer(&cdns_uart->timer, jiffies);
+		}
+	} else {
+		cdns_uart_handle_tx(port);
 
-	/* Enable the TX Empty interrupt */
-	writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_IER);
+		/* Enable the TX Empty interrupt */
+		writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_IER);
+	}
+}
+
+/**
+ * cdns_rs485_stop_tx_callback - Timer stop tx callback handler for rs485.
+ * @t: Handle to the timer list structure
+ */
+static void cdns_rs485_stop_tx_callback(struct timer_list *t)
+{
+	unsigned int regval;
+	struct cdns_uart *cdns_uart = from_timer(cdns_uart, t, stop_tx_timer);
+
+	cdns_rs485_rx_setup(cdns_uart);
+
+	regval = readl(cdns_uart->port->membase + CDNS_UART_CR);
+	regval |= CDNS_UART_CR_TX_DIS;
+	/* Disable the transmitter */
+	writel(regval, cdns_uart->port->membase + CDNS_UART_CR);
 }
 
 /**
@@ -617,11 +751,19 @@ static void cdns_uart_start_tx(struct uart_port *port)
 static void cdns_uart_stop_tx(struct uart_port *port)
 {
 	unsigned int regval;
+	struct cdns_uart *cdns_uart = port->private_data;
 
-	regval = readl(port->membase + CDNS_UART_CR);
-	regval |= CDNS_UART_CR_TX_DIS;
-	/* Disable the transmitter */
-	writel(regval, port->membase + CDNS_UART_CR);
+	if ((cdns_uart->port->rs485.flags & SER_RS485_ENABLED) &&
+	    !timer_pending(&cdns_uart->stop_tx_timer) &&
+	    cdns_uart->rs485_tx_started) {
+		mod_timer(&cdns_uart->stop_tx_timer, jiffies +
+			  msecs_to_jiffies(cdns_uart->port->rs485.delay_rts_after_send));
+	} else {
+		regval = readl(port->membase + CDNS_UART_CR);
+		regval |= CDNS_UART_CR_TX_DIS;
+		/* Disable the transmitter */
+		writel(regval, port->membase + CDNS_UART_CR);
+	}
 }
 
 /**
@@ -829,6 +971,12 @@ 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) {
+		timer_setup(&cdns_uart->stop_tx_timer,
+			    cdns_rs485_stop_tx_callback, 0);
+		cdns_rs485_rx_setup(cdns_uart);
+	}
+
 	/*
 	 * Clear the RX disable bit and then set the RX enable bit to enable
 	 * the receiver.
@@ -888,6 +1036,7 @@ static void cdns_uart_shutdown(struct uart_port *port)
 {
 	int status;
 	unsigned long flags;
+	struct cdns_uart *cdns_uart = port->private_data;
 
 	uart_port_lock_irqsave(port, &flags);
 
@@ -903,6 +1052,11 @@ static void cdns_uart_shutdown(struct uart_port *port)
 	uart_port_unlock_irqrestore(port, flags);
 
 	free_irq(port->irq, port);
+
+	if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED) {
+		del_timer_sync(&cdns_uart->timer);
+		del_timer_sync(&cdns_uart->stop_tx_timer);
+	}
 }
 
 /**
@@ -1032,7 +1186,7 @@ static void cdns_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	mode_reg &= ~CDNS_UART_MR_CHMODE_MASK;
 
 	if (mctrl & TIOCM_RTS)
-		val |= CDNS_UART_MODEMCR_RTS;
+		cdns_rts_gpio_enable(cdns_uart_data, 1);
 	if (mctrl & TIOCM_DTR)
 		val |= CDNS_UART_MODEMCR_DTR;
 	if (mctrl & TIOCM_LOOP)
@@ -1455,6 +1609,31 @@ 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)
+{
+	u32 val;
+
+	if (rs485->flags & SER_RS485_ENABLED) {
+		dev_dbg(port->dev, "Setting UART to RS485\n");
+		/* Make sure auto RTS is disabled */
+		val = readl(port->membase + CDNS_UART_MODEMCR);
+		val &= ~CDNS_UART_MODEMCR_FCM;
+		writel(val, port->membase + CDNS_UART_MODEMCR);
+		/* Disable transmitter and make Rx setup*/
+		cdns_uart_stop_tx(port);
+	}
+	return 0;
+}
+
 /**
  * cdns_uart_probe - Platform driver probe
  * @pdev: Pointer to the platform device structure
@@ -1597,9 +1776,23 @@ 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_rts = devm_gpiod_get_optional(&pdev->dev, "rts",
+							    GPIOD_OUT_LOW);
+	if (IS_ERR(cdns_uart_data->gpiod_rts)) {
+		rc = PTR_ERR(cdns_uart_data->gpiod_rts);
+		dev_err(port->dev, "xuartps: devm_gpiod_get_optional failed\n");
+		goto err_out_clk_notifier;
+	}
+
 	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_set_autosuspend_delay(&pdev->dev, UART_AUTOSUSPEND_TIMEOUT);
 	pm_runtime_set_active(&pdev->dev);
@@ -1618,6 +1811,8 @@ static int cdns_uart_probe(struct platform_device *pdev)
 		console_port = port;
 	}
 #endif
+	if (cdns_uart_data->port->rs485.flags & SER_RS485_ENABLED)
+		cdns_rs485_rx_setup(cdns_uart_data);
 
 	rc = uart_add_one_port(&cdns_uart_uart_driver, port);
 	if (rc) {
@@ -1646,6 +1841,7 @@ 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