[PATCH V2 0/2] Add rs485 support to uartps driver

[PATCH V2 0/2] Add rs485 support to uartps driver

[Manikanta Guntupalli]

Add optional gpio property to uartps node to support rs485.
Add rs485 support to uartps driver.
---
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.

Manikanta Guntupalli (2):
  dt-bindings: Add optional gpio property to uartps node to support
    rs485
  tty: serial: uartps: Add rs485 support to uartps driver

 .../devicetree/bindings/serial/cdns,uart.yaml |   6 +
 drivers/tty/serial/xilinx_uartps.c            | 116 +++++++++++++++++-
 2 files changed, 121 insertions(+), 1 deletion(-)

-- 
2.25.1

[PATCH V2 1/2] dt-bindings: Add optional gpio property to uartps node to support rs485

[Manikanta Guntupalli]

Add optional gpio property to uartps node and reference to rs485.yaml

On Xilinx/AMD Kria SOM KD240 board rs485 connects via TI ISOW1432
Transceiver device, where one GPIO is used for driving DE/RE signals.
With rs485 half duplex configuration, DE and RE shorts to each other,
and at a time, any node acts as either a driver or a receiver.

Here,
DE - Driver enable. If pin is floating, driver is disabled.
RE - Receiver enable. If pin is floating, receiver buffer is disabled.

For more deatils, please find below link which contains Transceiver
device(ISOW1432) datasheet
https://www.ti.com/lit/ds/symlink/isow1432.pdf?ts=1682607122706&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FISOW1432%252Fpart-details%252FISOW1432DFMR%253FkeyMatch%253DISOW1432DFMR%2526tisearch%253Dsearch-everything%2526usecase%253DOPN

xlnx,phy-ctrl-gpios is optional property, because it is not required
for uart console node.

Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@amd.com>
---
Changes for V2:
Modify optional gpio name to xlnx,phy-ctrl-gpios.
Update commit description.
---
 Documentation/devicetree/bindings/serial/cdns,uart.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/serial/cdns,uart.yaml b/Documentation/devicetree/bindings/serial/cdns,uart.yaml
index a8b323d7bf94..cf8ef55ba210 100644
--- a/Documentation/devicetree/bindings/serial/cdns,uart.yaml
+++ b/Documentation/devicetree/bindings/serial/cdns,uart.yaml
@@ -46,6 +46,11 @@ properties:
   power-domains:
     maxItems: 1
 
+  xlnx,phy-ctrl-gpios:
+    description: Optional GPIO to control transmit/receive on RS485 phy
+      in halfduplex mode.
+    maxItems: 1
+
 required:
   - compatible
   - reg
@@ -55,6 +60,7 @@ required:
 
 allOf:
   - $ref: serial.yaml#
+  - $ref: rs485.yaml#
   - if:
       properties:
         compatible:
-- 
2.25.1

Re: [PATCH V2 1/2] dt-bindings: Add optional gpio property to uartps node to support rs485

[m.brock]

Manikanta Guntupalli wrote on 2023-10-11 16:56:
> Add optional gpio property to uartps node and reference to rs485.yaml
> 
> On Xilinx/AMD Kria SOM KD240 board rs485 connects via TI ISOW1432
> Transceiver device, where one GPIO is used for driving DE/RE signals.
> With rs485 half duplex configuration, DE and RE shorts to each other,

s/shorts/are connected

> and at a time, any node acts as either a driver or a receiver.
> 
> Here,
> DE - Driver enable. If pin is floating, driver is disabled.
> RE - Receiver enable. If pin is floating, receiver buffer is disabled.

Please use DE and /RE to indicate DE is active high and /RE is active 
low.

> xlnx,phy-ctrl-gpios is optional property, because it is not required
> for uart console node.

How about introducing an rs485 generic gpios property instead of xlnx
private one? See also rs485-term-gpios and rs485-rx-during-tx-gpios.

Also note that every kernel driver expects to use RTS for this purpose.
So why not give this driver the option to choose a gpio instead of its
native RTS? And from there on use the rts route?
What if someone wants to use normal (non-rs485) RTS on a GPIO instead
of the native pin?

@Rob Herring
I am curious to know how the rs485 maintainers look at this.

Maarten

Re: [PATCH V2 1/2] dt-bindings: Add optional gpio property to uartps node to support rs485

[Rob Herring]

On Thu, Oct 12, 2023 at 08:35:59PM +0200, m.brock@vanmierlo.com wrote:
> Manikanta Guntupalli wrote on 2023-10-11 16:56:
> > Add optional gpio property to uartps node and reference to rs485.yaml
> > 
> > On Xilinx/AMD Kria SOM KD240 board rs485 connects via TI ISOW1432
> > Transceiver device, where one GPIO is used for driving DE/RE signals.
> > With rs485 half duplex configuration, DE and RE shorts to each other,
> 
> s/shorts/are connected
> 
> > and at a time, any node acts as either a driver or a receiver.
> > 
> > Here,
> > DE - Driver enable. If pin is floating, driver is disabled.
> > RE - Receiver enable. If pin is floating, receiver buffer is disabled.
> 
> Please use DE and /RE to indicate DE is active high and /RE is active low.
> 
> > xlnx,phy-ctrl-gpios is optional property, because it is not required
> > for uart console node.
> 
> How about introducing an rs485 generic gpios property instead of xlnx
> private one? See also rs485-term-gpios and rs485-rx-during-tx-gpios.
> 
> Also note that every kernel driver expects to use RTS for this purpose.
> So why not give this driver the option to choose a gpio instead of its
> native RTS? And from there on use the rts route?
> What if someone wants to use normal (non-rs485) RTS on a GPIO instead
> of the native pin?
> 
> @Rob Herring
> I am curious to know how the rs485 maintainers look at this.

Ask them.

We already have 'rts-gpios'. If that's what's always used, then perhaps 
we should use that in the RS485 case too?

Rob

Re: [PATCH V2 1/2] dt-bindings: Add optional gpio property to uartps node to support rs485

[m.brock]

Rob Herring wrote on 2023-10-12 22:51:
>> How about introducing an rs485 generic gpios property instead of xlnx
>> private one? See also rs485-term-gpios and rs485-rx-during-tx-gpios.
>> 
>> Also note that every kernel driver expects to use RTS for this 
>> purpose.
>> So why not give this driver the option to choose a gpio instead of its
>> native RTS? And from there on use the rts route?
>> What if someone wants to use normal (non-rs485) RTS on a GPIO instead
>> of the native pin?
>> 
>> @Rob Herring
>> I am curious to know how the rs485 maintainers look at this.
> 
> Ask them.

Funny, your name is the only one listed under the maintainers in
Documentation/devicetree/bindings/serial/rs485.yaml

And there is no mention of (RS-)485 in MAINTAINERS.

> We already have 'rts-gpios'. If that's what's always used, then perhaps
> we should use that in the RS485 case too?
> 
> Rob

Sounds like a good idea.

Maarten

[PATCH V2 2/2] tty: serial: uartps: Add rs485 support to uartps driver

[Manikanta Guntupalli]

In RS485 half duplex configuration, DriverEnable and ReceiverEnable
shorted to each other, and at a time, any node acts as either a driver
or a receiver. Use either xlnx,phy-ctrl-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.
---
 drivers/tty/serial/xilinx_uartps.c | 116 ++++++++++++++++++++++++++++-
 1 file changed, 115 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 8e521c69a959..abddcf1a8bf4 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -23,6 +23,7 @@
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
 #include <linux/iopoll.h>
+#include <linux/gpio.h>
 
 #define CDNS_UART_TTY_NAME	"ttyPS"
 #define CDNS_UART_NAME		"xuartps"
@@ -193,6 +194,7 @@ 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 +205,19 @@ 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 +316,42 @@ 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)
+{
+	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_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)
+{
+	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);
+	}
+}
+
+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 +360,20 @@ 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 (cdns_uart->port->rs485.delay_rts_before_send)
+			mdelay(cdns_uart->port->rs485.delay_rts_before_send);
+	}
+
 	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 +387,23 @@ 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);
+		if (cdns_uart->port->rs485.delay_rts_after_send)
+			mdelay(cdns_uart->port->rs485.delay_rts_after_send);
+	}
 }
 
 /**
@@ -829,6 +901,9 @@ 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 +1530,25 @@ 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 +1691,28 @@ 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, "xlnx,phy-ctrl",
+							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 +1759,7 @@ 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

Re: [PATCH V2 2/2] tty: serial: uartps: Add rs485 support to uartps driver

[m.brock]

Manikanta Guntupalli wrote on 2023-10-11 16:56:
> In RS485 half duplex configuration, DriverEnable and ReceiverEnable
> shorted to each other, and at a time, any node acts as either a driver
> or a receiver. Use either xlnx,phy-ctrl-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.
> ---
>  drivers/tty/serial/xilinx_uartps.c | 116 ++++++++++++++++++++++++++++-
>  1 file changed, 115 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/xilinx_uartps.c
> b/drivers/tty/serial/xilinx_uartps.c
> index 8e521c69a959..abddcf1a8bf4 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -23,6 +23,7 @@
>  #include <linux/module.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/iopoll.h>
> +#include <linux/gpio.h>
> 
>  #define CDNS_UART_TTY_NAME	"ttyPS"
>  #define CDNS_UART_NAME		"xuartps"
> @@ -193,6 +194,7 @@ 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 +205,19 @@ 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,

You promise here to support both RTS-on-send and RTS-after-send, but...

> +	.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 +316,42 @@ 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)
> +{
> +	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);

Here you don't care about RTS-on-send or RTS-after-send anymore.
And neither do you btw. in the if clause.

> +	}
> +}
> +
> +/**
> + * 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)
> +{
> +	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);
> +	}

Same here.

> +}
> +
> +static unsigned int cdns_uart_tx_empty(struct uart_port *port);
> +

I think it's better to move up the implementation than to use a forward
declaration.

>  /**
>   * cdns_uart_handle_tx - Handle the bytes to be Txed.
>   * @dev_id: Id of the UART port
> @@ -313,12 +360,20 @@ 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 (cdns_uart->port->rs485.delay_rts_before_send)
> +			mdelay(cdns_uart->port->rs485.delay_rts_before_send);

mdelay?
https://www.kernel.org/doc/html/latest/timers/timers-howto.html
"In general, use of mdelay is discouraged and code should be refactored 
to
allow for the use of msleep."

Furthermore, you're delaying before every burst of bytes here!
Every TXEMPTY interrupt!

> +	}
> +
>  	if (uart_circ_empty(xmit)) {
>  		writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_IDR);
> -		return;
> +		goto rs485_rx_setup;

And when there was nothing more to send you waited for nothing.

>  	}
> 
>  	numbytes = port->fifosize;
> @@ -332,6 +387,23 @@ 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);
> +		if (cdns_uart->port->rs485.delay_rts_after_send)
> +			mdelay(cdns_uart->port->rs485.delay_rts_after_send);

This is not delaying rts after send. You must keep RTS aka DE active for 
a little
longer so even the last stop bit(s) are transmitted correctly. So this 
delay must
happen before cdns_rs485_rx_setup().

> +	}
>  }
> 
>  /**
> @@ -829,6 +901,9 @@ 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 +1530,25 @@ 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 +1691,28 @@ 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, 
> "xlnx,phy-ctrl",
> +							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 +1759,7 @@ 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);

Maarten

RE: [PATCH V2 2/2] tty: serial: uartps: Add rs485 support to uartps driver

[Guntupalli, Manikanta]

Hi,

> -----Original Message-----
> From: m.brock@vanmierlo.com <m.brock@vanmierlo.com>
> Sent: Friday, October 13, 2023 12:35 AM
> To: Guntupalli, Manikanta <manikanta.guntupalli@amd.com>
> Cc: git (AMD-Xilinx) <git@amd.com>; Simek, Michal
> <michal.simek@amd.com>; gregkh@linuxfoundation.org;
> robh+dt@kernel.org; krzysztof.kozlowski+dt@linaro.org;
> conor+dt@kernel.org; linux-serial@vger.kernel.org;
> devicetree@vger.kernel.org; linux-kernel@vger.kernel.org;
> jirislaby@kernel.org; linux-arm-kernel@lists.infradead.org; Pandey, Radhey
> Shyam <radhey.shyam.pandey@amd.com>; Goud, Srinivas
> <srinivas.goud@amd.com>; Datta, Shubhrajyoti
> <shubhrajyoti.datta@amd.com>; manion05gk@gmail.com
> Subject: Re: [PATCH V2 2/2] tty: serial: uartps: Add rs485 support to uartps
> driver
> 
> Manikanta Guntupalli wrote on 2023-10-11 16:56:
> > In RS485 half duplex configuration, DriverEnable and ReceiverEnable
> > shorted to each other, and at a time, any node acts as either a driver
> > or a receiver. Use either xlnx,phy-ctrl-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.
> > ---
> >  drivers/tty/serial/xilinx_uartps.c | 116
> > ++++++++++++++++++++++++++++-
> >  1 file changed, 115 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/serial/xilinx_uartps.c
> > b/drivers/tty/serial/xilinx_uartps.c
> > index 8e521c69a959..abddcf1a8bf4 100644
> > --- a/drivers/tty/serial/xilinx_uartps.c
> > +++ b/drivers/tty/serial/xilinx_uartps.c
> > @@ -23,6 +23,7 @@
> >  #include <linux/module.h>
> >  #include <linux/pm_runtime.h>
> >  #include <linux/iopoll.h>
> > +#include <linux/gpio.h>
> >
> >  #define CDNS_UART_TTY_NAME	"ttyPS"
> >  #define CDNS_UART_NAME		"xuartps"
> > @@ -193,6 +194,7 @@ 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 +205,19 @@ 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,
> 
> You promise here to support both RTS-on-send and RTS-after-send, but...
> 
> > +	.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 +316,42 @@ 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) {
> > +	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);
> 
> Here you don't care about RTS-on-send or RTS-after-send anymore.
> And neither do you btw. in the if clause.
On Xilinx/AMD Kria SOM KD240 board rs485 connects via TI ISOW1432
Transceiver device, where one GPIO is used for driving DE/RE signals.
With rs485 half duplex configuration, DE and RE shorted to each other,
and at a time, any node acts as either a driver or a receiver.
We recommend using either GPIO or RTS to control RS485 phy as driver or a
receiver. So, we fall back to RTS, if rts-gpios not passed.
> 
> > +	}
> > +}
> > +
> > +/**
> > + * 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) {
> > +	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);
> > +	}
> 
> Same here.
> 
> > +}
> > +
> > +static unsigned int cdns_uart_tx_empty(struct uart_port *port);
> > +
> 
> I think it's better to move up the implementation than to use a forward
> declaration.
We will fix.
> 
> >  /**
> >   * cdns_uart_handle_tx - Handle the bytes to be Txed.
> >   * @dev_id: Id of the UART port
> > @@ -313,12 +360,20 @@ 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 (cdns_uart->port->rs485.delay_rts_before_send)
> > +			mdelay(cdns_uart->port-
> >rs485.delay_rts_before_send);
> 
> mdelay?
> https://www.kernel.org/doc/html/latest/timers/timers-howto.html
> "In general, use of mdelay is discouraged and code should be refactored to
> allow for the use of msleep."
For refactoring the code will move this code snippet to start_tx, even there,
interrupts are disabled, so can't use msleep.

https://docs.kernel.org/driver-api/serial/driver.html
Documentation recommends,
start_tx
void ()(struct uart_port *port)
Start transmitting characters.
Locking: port->lock taken. Interrupts: locally disabled. This call must not sleep.

> 
> Furthermore, you're delaying before every burst of bytes here!
> Every TXEMPTY interrupt!
We will move code to start_tx.
> 
> > +	}
> > +
> >  	if (uart_circ_empty(xmit)) {
> >  		writel(CDNS_UART_IXR_TXEMPTY, port->membase +
> CDNS_UART_IDR);
> > -		return;
> > +		goto rs485_rx_setup;
> 
> And when there was nothing more to send you waited for nothing.
We will fix.
> 
> >  	}
> >
> >  	numbytes = port->fifosize;
> > @@ -332,6 +387,23 @@ 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);
> > +		if (cdns_uart->port->rs485.delay_rts_after_send)
> > +			mdelay(cdns_uart->port-
> >rs485.delay_rts_after_send);
> 
> This is not delaying rts after send. You must keep RTS aka DE active for a little
> longer so even the last stop bit(s) are transmitted correctly. So this delay must
> happen before cdns_rs485_rx_setup().
We will fix.
> 
> > +	}
> >  }
> >
> >  /**
> > @@ -829,6 +901,9 @@ 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 +1530,25 @@ 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
> > +1691,28 @@ 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,
> > "xlnx,phy-ctrl",
> > +							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 +1759,7 @@ 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);
> 
> Maarten


Thanks,
Manikanta.

Re: [PATCH V2 2/2] tty: serial: uartps: Add rs485 support to uartps driver

[Lino Sanfilippo]

On 11.10.23 at 16:56, Manikanta Guntupalli wrote:
> In RS485 half duplex configuration, DriverEnable and ReceiverEnable
> shorted to each other, and at a time, any node acts as either a driver
> or a receiver. Use either xlnx,phy-ctrl-gpios or RTS to control
> RS485 phy as driver or a receiver.

This is a very specific hardware setup. RS485 is supposed to work with various
hardware configurations though. So the above assumptions must not be hardcoded
in the RS485 implementation (as it is in cdns_rs485_rx_setup() and cdns_rs485_tx_setup()
IIUC)

>
> 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.
> ---
>  drivers/tty/serial/xilinx_uartps.c | 116 ++++++++++++++++++++++++++++-
>  1 file changed, 115 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> index 8e521c69a959..abddcf1a8bf4 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -23,6 +23,7 @@
>  #include <linux/module.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/iopoll.h>
> +#include <linux/gpio.h>
>
>  #define CDNS_UART_TTY_NAME	"ttyPS"
>  #define CDNS_UART_NAME		"xuartps"
> @@ -193,6 +194,7 @@ 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 +205,19 @@ 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 +316,42 @@ 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)
> +{
> +	u32 val;
> +
> +	if (cdns_uart->gpiod) {

If both RTS_ON_SEND and RTS_AFTER_SEND are supported than you have to set the
GPIO value here depending on which one is currently configured. Note that
userspace may change RTS mode via TIOCSRS485 ioctl.

> +		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);

Same for the native RTS case.

> +	}
> +}
> +
> +/**
> + * 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)
> +{
> +	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);
> +	}

See above.


> +}
> +
> +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 +360,20 @@ 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 (cdns_uart->port->rs485.delay_rts_before_send)
> +			mdelay(cdns_uart->port->rs485.delay_rts_before_send);
> +	}
> +
>  	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 +387,23 @@ 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);
> +		if (cdns_uart->port->rs485.delay_rts_after_send)
> +			mdelay(cdns_uart->port->rs485.delay_rts_after_send);
> +	}
>  }
>
>  /**
> @@ -829,6 +901,9 @@ 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 +1530,25 @@ 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;
> +

This assignment is not needed, the serial core will do that.

> +	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 +1691,28 @@ 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, "xlnx,phy-ctrl",
> +							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 using the GPIO is optional, why not fall back to the use of the native RTS?

> +	if (cdns_uart_data->gpiod) {
> +		gpiod_direction_output(cdns_uart_data->gpiod, GPIOD_OUT_LOW);
> +		gpiod_set_value(cdns_uart_data->gpiod, 0);

You already set both of these attributes when you requested the GPIO.

> +	}
> +
>  	pm_runtime_use_autosuspend(&pdev->dev);
>  	pm_runtime_set_autosuspend_delay(&pdev->dev, UART_AUTOSUSPEND_TIMEOUT);
>  	pm_runtime_set_active(&pdev->dev);
> @@ -1646,6 +1759,7 @@ 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);
>

Regards,
Lino