Commit d58a2df3 authored by Lukas Wunner's avatar Lukas Wunner Committed by Greg Kroah-Hartman
Browse files

serial: 8250: Support rs485 bus termination GPIO 



Commit e8759ad1 ("serial: uapi: Add support for bus termination")
introduced the ability to enable rs485 bus termination from user space.
So far the feature is only used by a single driver, 8250_exar.c, using a
hardcoded GPIO pin specific to Siemens IOT2040 products.

Provide for a more generic solution by allowing specification of an
rs485 bus termination GPIO pin in the device tree:  Amend the serial
core to retrieve the GPIO from the device tree (or ACPI table) and amend
the default ->rs485_config() callback for 8250 drivers to change the
GPIO on request from user space.

Perhaps 8250_exar.c can be converted to the generic approach in a
follow-up patch.

Signed-off-by: default avatarLukas Wunner <lukas@wunner.de>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Link: https://lore.kernel.org/r/94c6c800d1ca9fa04766dd1d43a8272c5ad4bedd.1589811297.git.lukas@wunner.de


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f40a6be4

drivers/tty/serial/8250/8250_port.c

+3 −0
Original line number Diff line number Diff line
@@ -681,6 +681,9 @@ int serial8250_em485_config(struct uart_port *port, struct serial_rs485 *rs485) 
	memset(rs485->padding, 0, sizeof(rs485->padding));

	port->rs485 = *rs485;



	gpiod_set_value(port->rs485_term_gpio,

			rs485->flags & SER_RS485_TERMINATE_BUS);



	/*

	 * Both serial8250_em485_init() and serial8250_em485_destroy()

	 * are idempotent.

drivers/tty/serial/serial_core.c

+16 −0
Original line number Diff line number Diff line
@@ -3317,6 +3317,7 @@ int uart_get_rs485_mode(struct uart_port *port) 
	 * to get to a defined state with the following properties:

	 */

	rs485conf->flags &= ~(SER_RS485_RX_DURING_TX | SER_RS485_ENABLED |

			      SER_RS485_TERMINATE_BUS |

			      SER_RS485_RTS_AFTER_SEND);

	rs485conf->flags |= SER_RS485_RTS_ON_SEND;
@@ -3331,6 +3332,21 @@ int uart_get_rs485_mode(struct uart_port *port) 
		rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;

	}



	/*

	 * Disabling termination by default is the safe choice:  Else if many

	 * bus participants enable it, no communication is possible at all.

	 * Works fine for short cables and users may enable for longer cables.

	 */

	port->rs485_term_gpio = devm_gpiod_get_optional(dev, "rs485-term",

							GPIOD_OUT_LOW);

	if (IS_ERR(port->rs485_term_gpio)) {

		ret = PTR_ERR(port->rs485_term_gpio);

		port->rs485_term_gpio = NULL;

		if (ret != -EPROBE_DEFER)

			dev_err(dev, "Cannot get rs485-term-gpios\n");

		return ret;

	}



	return 0;

}

EXPORT_SYMBOL_GPL(uart_get_rs485_mode);

include/linux/serial_core.h

+2 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/bitops.h>

#include <linux/compiler.h>

#include <linux/console.h>

#include <linux/gpio/consumer.h>

#include <linux/interrupt.h>

#include <linux/circ_buf.h>

#include <linux/spinlock.h>
@@ -251,6 +252,7 @@ struct uart_port { 
	struct attribute_group	*attr_group;		/* port specific attributes */

	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */

	struct serial_rs485     rs485;

	struct gpio_desc	*rs485_term_gpio;	/* enable RS485 bus termination */

	struct serial_iso7816   iso7816;

	void			*private_data;		/* generic platform data pointer */

};

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