RE: [PATCH V8 3/3] tty: serial: uartps: Add rs485 support to uartps driver

[Guntupalli, Manikanta]

Hi,

> -----Original Message-----
> From: Maarten Brock <m.brock@xxxxxxxxxxxxx>
> Sent: Wednesday, January 10, 2024 7:10 PM
> To: Guntupalli, Manikanta <manikanta.guntupalli@xxxxxxx>
> Cc: git (AMD-Xilinx) <git@xxxxxxx>; Simek, Michal
> <michal.simek@xxxxxxx>; gregkh@xxxxxxxxxxxxxxxxxxx;
> robh+dt@xxxxxxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx;
> conor+dt@xxxxxxxxxx; linux-serial@xxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> jirislaby@xxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Pandey, Radhey
> Shyam <radhey.shyam.pandey@xxxxxxx>; Goud, Srinivas
> <srinivas.goud@xxxxxxx>; Datta, Shubhrajyoti
> <shubhrajyoti.datta@xxxxxxx>; manion05gk@xxxxxxxxx
> Subject: Re: [PATCH V8 3/3] tty: serial: uartps: Add rs485 support to uartps
> driver
> 
> Manikanta Guntupalli wrote on 2024-01-10 12:11:
> > Changes for V8:
> > Use hrtimer instead of timer list.
> > Simplify cdns_rs485_tx_setup() and cdns_rs485_rx_setup().
> > Update argument of cdns_rts_gpio_enable() in cdns_uart_set_mctrl().
> > Add cdns_calc_after_tx_delay() to calculate required delay after tx.
> > Add hrtimer setup in cdns_rs485_config().
> > Move enable TX Empty interrupt and rs485 rx callback scheduling part
> > to cdns_uart_handle_tx().
> > ---
> >  drivers/tty/serial/xilinx_uartps.c | 241
> > ++++++++++++++++++++++++++++-
> >  1 file changed, 233 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/tty/serial/xilinx_uartps.c
> > b/drivers/tty/serial/xilinx_uartps.c
> > index aafcc2179e0e..3247fd3e91fd 100644
> > --- a/drivers/tty/serial/xilinx_uartps.c
> > +++ b/drivers/tty/serial/xilinx_uartps.c
> > @@ -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
> > + * @tx_timer:		Timer for tx
> 
> start_tx_timer ?
We are using tx_timer before TX start and after TX done.
> 
> > + * @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 hrtimer		tx_timer;
> > +	struct hrtimer		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) {
> > +	bool enable;
> > +
> > +	enable = cdns_uart->port->rs485.flags & SER_RS485_RTS_ON_SEND;
> > +	cdns_rts_gpio_enable(cdns_uart, enable);
> > +
> > +	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) {
> > +	bool enable;
> > +
> > +	enable = cdns_uart->port->rs485.flags &
> SER_RS485_RTS_AFTER_SEND;
> > +	cdns_rts_gpio_enable(cdns_uart, enable);
> > +
> > +	cdns_uart->rs485_tx_started = false; }
> > +
> >  /**
> >   * cdns_uart_tx_empty -  Check whether TX is empty
> >   * @port: Handle to the uart port structure @@ -320,6 +387,37 @@
> > static unsigned int cdns_uart_tx_empty(struct uart_port *port)
> >  	return (status == CDNS_UART_SR_TXEMPTY) ? TIOCSER_TEMT : 0;  }
> >
> > +/**
> > + * cdns_rs485_rx_callback - Timer rx callback handler for rs485.
> > + * @t: Handle to the hrtimer structure  */ static enum
> > +hrtimer_restart cdns_rs485_rx_callback(struct hrtimer *t) {
> > +	struct cdns_uart *cdns_uart = container_of(t, struct cdns_uart,
> > tx_timer);
> > +
> > +	/*
> > +	 * Default Rx should be setup, because Rx signaling path
> > +	 * need to enable to receive data.
> > +	 */
> > +	cdns_rs485_rx_setup(cdns_uart);
> > +
> > +	return HRTIMER_NORESTART;
> > +}
> > +
> > +/**
> > + * cdns_calc_after_tx_delay - calculate delay required for after tx.
> > + * @cdns_uart: Handle to the cdns_uart  */ static u64
> > +cdns_calc_after_tx_delay(struct cdns_uart *cdns_uart) {
> > +	/*
> > +	 * Frame time + stop bit time + rs485.delay_rts_after_send
> > +	 */
> > +	return cdns_uart->port->frame_time
> > +	       + DIV_ROUND_UP(cdns_uart->port->frame_time, 7)
> > +	       + (u64)cdns_uart->port->rs485.delay_rts_after_send *
> > NSEC_PER_MSEC;
> > +}
> > +
> >  /**
> >   * cdns_uart_handle_tx - Handle the bytes to be Txed.
> 
> s/Txed/transmitted
We will fix.
> 
> >   * @dev_id: Id of the UART port
> > @@ -328,6 +426,7 @@ static unsigned int cdns_uart_tx_empty(struct
> > uart_port *port)  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 int numbytes;
> 
> I recommend to also check uart_tx_stopped() for disabling the TXEMPTY
> interrupt.
We will fix.
> 
> -	if (uart_circ_empty(xmit)) {
> +	if (uart_circ_empty(xmit) || uart_tx_stopped(port)) {
> +		/* Disable the TX Empty interrupt */
> 		writel(CDNS_UART_IXR_TXEMPTY, port->membase +
> CDNS_UART_IDR);
> 		return;
> 	}
> 
> > @@ -347,6 +446,16 @@ static void cdns_uart_handle_tx(void *dev_id)
> >
> >  	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
> >  		uart_write_wakeup(port);
> > +
> > +	/* Enable the TX Empty interrupt */
> > +	writel(CDNS_UART_IXR_TXEMPTY, cdns_uart->port->membase +
> > CDNS_UART_IER);
> > +
> > +	if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED &&
> > +	    (uart_circ_empty(xmit) || uart_tx_stopped(port))) {
> > +		cdns_uart->tx_timer.function = &cdns_rs485_rx_callback;
> > +		hrtimer_start(&cdns_uart->tx_timer,
> > +
> ns_to_ktime(cdns_calc_after_tx_delay(cdns_uart)),
> > HRTIMER_MODE_REL);
> > +	}
> >  }
> >
> >  /**
> > @@ -579,6 +688,21 @@ static int cdns_uart_clk_notifier_cb(struct
> > notifier_block *nb,  }  #endif
> >
> > +/**
> > + * cdns_rs485_tx_callback - Timer tx callback handler for rs485.
> > + * @t: Handle to the hrtimer structure  */ static enum
> > +hrtimer_restart cdns_rs485_tx_callback(struct hrtimer *t) {
> > +	struct cdns_uart *cdns_uart = container_of(t, struct cdns_uart,
> > tx_timer);
> > +
> > +	uart_port_lock(cdns_uart->port);
> > +	cdns_uart_handle_tx(cdns_uart->port);
> > +	uart_port_unlock(cdns_uart->port);
> > +
> > +	return HRTIMER_NORESTART;
> > +}
> > +
> >  /**
> >   * cdns_uart_start_tx -  Start transmitting bytes
> >   * @port: Handle to the uart port structure @@ -586,6 +710,7 @@
> > 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 +729,38 @@ static void cdns_uart_start_tx(struct uart_port
> > *port)
> >
> 
> Maybe add comment here that the following clears the interrupt flag.
We will fix.
> 
> >  	writel(CDNS_UART_IXR_TXEMPTY, port->membase +
> CDNS_UART_ISR);
> >
> > +	if (cdns_uart->port->rs485.flags & SER_RS485_ENABLED) {
> > +		if (!cdns_uart->rs485_tx_started) {
> > +			cdns_uart->tx_timer.function =
> &cdns_rs485_tx_callback;
> > +			cdns_rs485_tx_setup(cdns_uart);
> 
> Move cdns_rs485_tx_setup() out of this if clause to make sure DE is
> always active.
In bulk transfer case, start_tx get called multiple times. If we move cdns_rs485_tx_setup() out of this if clause, every time DE will be pulled high.
This changes were added on Lino Sanfilippo suggestion.

> 
> > +			return hrtimer_start(&cdns_uart->tx_timer,
> > +					     ms_to_ktime(port-
> >rs485.delay_rts_before_send),
> > +					     HRTIMER_MODE_REL);
> > +		} else {
> > +			if (hrtimer_get_remaining(&cdns_uart->tx_timer))
> > +				hrtimer_cancel(&cdns_uart->tx_timer);
> 
> You intend to stop the timer for cdns_rs485_rx_callback() here, but...
> What if the tx_timer is started for cdns_rs485_tx_callback()?
We will fix.
> 
> > +		}
> > +	}
> >  	cdns_uart_handle_tx(port);
> > +}
> >
> > -	/* 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 enum hrtimer_restart cdns_rs485_stop_tx_callback(struct hrtimer
> > *t)
> > +{
> > +	unsigned int regval;
> > +	struct cdns_uart *cdns_uart = container_of(t, struct cdns_uart,
> > 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);
> > +
> > +	return HRTIMER_NORESTART;
> >  }
> >
> >  /**
> > @@ -617,11 +770,21 @@ 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) {
> > +		if (cdns_uart->rs485_tx_started)
> > +			hrtimer_start(&cdns_uart->stop_tx_timer,
> > +
> ns_to_ktime(cdns_calc_after_tx_delay(cdns_uart)),
> > +				      HRTIMER_MODE_REL);
> 
> Why do you want to wait here? Should disabling the transmitter not be
> enough?
> My guess and hope is that it will result in the current transmission
> running to
> completion and then fire the TXEMPTY interrupt which will then start the
> timer for
> cdns_rs485_rx_callback(). I see no need for a separate timer here.
We will fix.
> 
> > +		else
> > +			cdns_rs485_stop_tx_callback(&cdns_uart-
> >stop_tx_timer);
> > +	} 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 +992,9 @@ 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.
> > @@ -888,6 +1054,7 @@ 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 +1070,11 @@ 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) {
> > +		hrtimer_cancel(&cdns_uart->tx_timer);
> > +		hrtimer_cancel(&cdns_uart->stop_tx_timer);
> > +	}
> 
> Should you not do this much earlier in this function?
We will fix.
> 
> >  }
> >
> >  /**
> > @@ -1032,7 +1204,7 @@ 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, mctrl & TIOCM_RTS);
> 
> Move this out of the if clause so the gpio can also get cleared.
> On top of that it should be inverted.
> But if there is no gpio defined this call will create a glitch on the
> RTS pin.
> cdns_rts_gpio_enable() can set CDNS_UART_MODEMCR_RTS to lower the
> RTS
> pin and
> then val will clear CDNS_UART_MODEMCR_RTS again leaving the RTS pin
> high.
> I suggest to use this instead:
> 	if (mctrl & TIOCM_RTS)
> 		val |= CDNS_UART_MODEMCR_RTS;
> +	if (cdns_uart->gpiod_rts) {
> +		gpiod_set_value(cdns_uart->gpiod_rts, !(mctrl &
> TIOCM_RTS));
We will fix.
> 
> >  	if (mctrl & TIOCM_DTR)
> >  		val |= CDNS_UART_MODEMCR_DTR;
> >  	if (mctrl & TIOCM_LOOP)
> > @@ -1455,6 +1627,42 @@ 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;
> > +	struct cdns_uart *cdns_uart = port->private_data;
> > +
> > +	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);
> > +
> > +		/* Timer setup */
> > +		hrtimer_init(&cdns_uart->tx_timer, CLOCK_MONOTONIC,
> > HRTIMER_MODE_REL);
> > +		hrtimer_init(&cdns_uart->stop_tx_timer,
> CLOCK_MONOTONIC,
> > HRTIMER_MODE_REL);
> > +		cdns_uart->tx_timer.function = &cdns_rs485_tx_callback;
> > +		cdns_uart->stop_tx_timer.function =
> &cdns_rs485_stop_tx_callback;
> > +
> > +		/* Disable transmitter and make Rx setup*/
> > +		cdns_uart_stop_tx(port);
> > +	} else {
> > +		hrtimer_cancel(&cdns_uart->tx_timer);
> > +		hrtimer_cancel(&cdns_uart->stop_tx_timer);
> > +	}
> > +	return 0;
> > +}
> > +
> >  /**
> >   * cdns_uart_probe - Platform driver probe
> >   * @pdev: Pointer to the platform device structure
> > @@ -1597,9 +1805,23 @@ 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 +1840,8 @@ 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 +1870,7 @@ 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);
> 
> This is getting big and some modifications are not rs485 related.
> I suggest to split them and get those applied first.
> My first modification would be to add support for the rts gpio.
We will fix.


Thanks,
Manikanta.