Message-ID: <97bfc5ee-6c07-4e4b-8192-f46c701a0604@gmx.de>
Date:   Sun, 12 Nov 2023 20:37:58 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Manikanta Guntupalli <manikanta.guntupalli@....com>, git@....com,
        michal.simek@....com, gregkh@...uxfoundation.org,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, linux-serial@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        jirislaby@...nel.org, linux-arm-kernel@...ts.infradead.org
Cc:     radhey.shyam.pandey@....com, srinivas.goud@....com,
        shubhrajyoti.datta@....com, manion05gk@...il.com
Subject: Re: [PATCH V3 2/2] tty: serial: uartps: Add rs485 support to uartps
 driver

Hi,

On 24.10.23 16:48, Manikanta Guntupalli wrote:
> 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@....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.
> ---
>  drivers/tty/serial/xilinx_uartps.c | 180 ++++++++++++++++++++++++++---
>  1 file changed, 165 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> index 9c13dac1d4d1..32229cf5c508 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -23,6 +23,9 @@
>  #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 +196,7 @@ 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 +207,19 @@ 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 | 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 +318,79 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus)
>  	tty_flip_buffer_push(&port->state->port);
>  }
>
> +/**
> + * cdns_rs485_config_gpio_rts_high - Configure GPIO/RTS to high
> + * @cdns_uart: Handle to the cdns_uart
> + */
> +static void cdns_rs485_config_gpio_rts_high(struct cdns_uart *cdns_uart)
> +{
> +	u32 val;
> +
> +	if (cdns_uart->gpiod) {
> +		gpiod_set_value(cdns_uart->gpiod, 1);
> +	} else {
> +		val = readl(cdns_uart->port->membase + CDNS_UART_MODEMCR);
> +		val &= ~CDNS_UART_MODEMCR_RTS;
> +		writel(val, cdns_uart->port->membase + CDNS_UART_MODEMCR);
> +	}
> +}
> +
> +/**
> + * cdns_rs485_config_gpio_rts_low - Configure GPIO/RTS to low
> + * @cdns_uart: Handle to the cdns_uart
> + */
> +static void cdns_rs485_config_gpio_rts_low(struct cdns_uart *cdns_uart)
> +{
> +	u32 val;
> +
> +	if (cdns_uart->gpiod) {
> +		gpiod_set_value(cdns_uart->gpiod, 0);
> +	} else {
> +		val = readl(cdns_uart->port->membase + CDNS_UART_MODEMCR);
> +		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_rs485_config_gpio_rts_high(cdns_uart);
> +	else
> +		cdns_rs485_config_gpio_rts_low(cdns_uart);
> +}
> +
> +/**
> + * 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_rs485_config_gpio_rts_high(cdns_uart);
> +	else
> +		cdns_rs485_config_gpio_rts_low(cdns_uart);
> +}
> +
> +/**
> + * cdns_uart_tx_empty -  Check whether TX is empty
> + * @port: Handle to the uart port structure
> + *
> + * Return: TIOCSER_TEMT on success, 0 otherwise
> + */
> +static unsigned int cdns_uart_tx_empty(struct uart_port *port)
> +{
> +	unsigned int status;
> +
> +	status = readl(port->membase + CDNS_UART_SR) &
> +		       (CDNS_UART_SR_TXEMPTY | CDNS_UART_SR_TACTIVE);
> +	return (status == CDNS_UART_SR_TXEMPTY) ? TIOCSER_TEMT : 0;
> +}
> +
>  /**
>   * cdns_uart_handle_tx - Handle the bytes to be Txed.
>   * @dev_id: Id of the UART port
> @@ -571,6 +657,8 @@ static int cdns_uart_clk_notifier_cb(struct notifier_block *nb,
>  static void cdns_uart_start_tx(struct uart_port *port)
>  {
>  	unsigned int status;
> +	unsigned long time_out;
> +	struct cdns_uart *cdns_uart = port->private_data;
>
>  	if (uart_tx_stopped(port))
>  		return;
> @@ -589,8 +677,31 @@ static void cdns_uart_start_tx(struct uart_port *port)
>
>  	writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_ISR);
>
> +	if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED) {
> +		cdns_rs485_tx_setup(cdns_uart);
> +		if (cdns_uart->port->rs485.delay_rts_before_send)
> +			mdelay(cdns_uart->port->rs485.delay_rts_before_send);

So, this will be executed each time (including the rts_before_send delay) the core wants
to send data? This is not how it is supposed to work: The tx setup (and the
delay before send) has to be done once when transmission starts. Note that when sending
a bulk of data the core may call cdns_uart_start_tx() several times before
it eventually calls cdns_uart_stop_tx() to stop the transmission.


> +	}
> +
>  	cdns_uart_handle_tx(port);
>
> +	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();
> +
> +		if (cdns_uart->port->rs485.delay_rts_after_send)
> +			mdelay(cdns_uart->port->rs485.delay_rts_after_send);
> +
> +		/*
> +		 * Default Rx should be setup, because RX signaling path
> +		 * need to enable to receive data.
> +		 */
> +		cdns_rs485_rx_setup(cdns_uart);
> +	}
> +
>  	/* Enable the TX Empty interrupt */
>  	writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_IER);
>  }
> @@ -602,6 +713,14 @@ 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;
> +
> +	if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED) {
> +		if (cdns_uart->port->rs485.delay_rts_after_send)
> +			mdelay(cdns_uart->port->rs485.delay_rts_after_send);
> +
> +		cdns_rs485_rx_setup(cdns_uart);
> +	}
>
>  	regval = readl(port->membase + CDNS_UART_CR);
>  	regval |= CDNS_UART_CR_TX_DIS;
> @@ -626,21 +745,6 @@ static void cdns_uart_stop_rx(struct uart_port *port)
>  	writel(regval, port->membase + CDNS_UART_CR);
>  }
>
> -/**
> - * cdns_uart_tx_empty -  Check whether TX is empty
> - * @port: Handle to the uart port structure
> - *
> - * Return: TIOCSER_TEMT on success, 0 otherwise
> - */
> -static unsigned int cdns_uart_tx_empty(struct uart_port *port)
> -{
> -	unsigned int status;
> -
> -	status = readl(port->membase + CDNS_UART_SR) &
> -		       (CDNS_UART_SR_TXEMPTY | CDNS_UART_SR_TACTIVE);
> -	return (status == CDNS_UART_SR_TXEMPTY) ? TIOCSER_TEMT : 0;
> -}
> -
>  /**
>   * cdns_uart_break_ctl - Based on the input ctl we have to start or stop
>   *			transmitting char breaks
> @@ -829,6 +933,9 @@ 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 +1562,23 @@ 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)
> +{
> +	if (rs485->flags & SER_RS485_ENABLED)
> +		dev_dbg(port->dev, "Setting UART to RS485\n");
> +
> +	return 0;
> +}

So what if userspace changes the RS485 configuration? When does it take effect?

> +
>  /**
>   * cdns_uart_probe - Platform driver probe
>   * @pdev: Pointer to the platform device structure
> @@ -1463,6 +1587,7 @@ static int instances;
>   */
>  static int cdns_uart_probe(struct platform_device *pdev)
>  {
> +	u32 val;
>  	int rc, id, irq;
>  	struct uart_port *port;
>  	struct resource *res;
> @@ -1597,9 +1722,23 @@ 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 = devm_gpiod_get_optional(&pdev->dev, "rts",
> +							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");

Why bail out with an error if having cdns_uart_data->gpiod is only optional?

> +		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);
> @@ -1638,6 +1777,16 @@ static int cdns_uart_probe(struct platform_device *pdev)
>  	cdns_uart_data->cts_override = of_property_read_bool(pdev->dev.of_node,
>  							     "cts-override");
>
> +	if (cdns_uart_data->port->rs485.flags & SER_RS485_ENABLED) {
> +		if (!cdns_uart_data->gpiod) {
> +			val = readl(cdns_uart_data->port->membase
> +				    + CDNS_UART_MODEMCR);
> +			val |= CDNS_UART_MODEMCR_RTS;
> +			writel(val, cdns_uart_data->port->membase
> +			       + CDNS_UART_MODEMCR);
> +		}
> +	}

This covers the RTS_AFTER_SEND mode. What if SER_RS485_RTS_ON_SEND is configured instead
(as it is the default set by uart_get_rs485_mode())? What if cdns_uart_data->gpiod exists?
Why not simply call cdns_rs485_rx_setup() which covers all these cases?
Note that uart_add_one_port() will call into the serial core and eventually result in an
initial call to the ports rs485_config function (see uart_rs485_config()). So maybe put the
initial configuration into that function and remove the above code. However
in this case

cdns_uart_data->cts_override = of_property_read_bool(pdev->dev.of_node,
							     "cts-override");
should be called before uart_add_one_port().


Regards,
Lino

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