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Subject[PATCH DON'T APPLY v2 3/7] serial: 8250: Support rs485 bus termination GPIO
Date
From: Lukas Wunner <lukas@wunner.de>

Amend the serial core to retrieve the rs485 bus termination 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.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
---
drivers/tty/serial/8250/8250_port.c | 5 +++++
drivers/tty/serial/serial_core.c | 25 +++++++++++++++++++++++++
include/linux/serial_core.h | 1 +
3 files changed, 31 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 4440867b7d20..47c059987538 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -30,6 +30,7 @@
#include <linux/uaccess.h>
#include <linux/pm_runtime.h>
#include <linux/ktime.h>
+#include <linux/gpio/consumer.h>

#include <asm/io.h>
#include <asm/irq.h>
@@ -681,6 +682,10 @@ int serial8250_em485_config(struct uart_port *port, struct serial_rs485 *rs485)
memset(rs485->padding, 0, sizeof(rs485->padding));
port->rs485 = *rs485;

+ if (port->rs485_term_gpio)
+ gpiod_set_value(port->rs485_term_gpio,
+ rs485->flags & SER_RS485_TERMINATE_BUS);
+
/*
* Both serial8250_em485_init() and serial8250_em485_destroy()
* are idempotent.
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 43b6682877d5..77702b6371e3 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -27,6 +27,7 @@

#include <linux/irq.h>
#include <linux/uaccess.h>
+#include <linux/gpio/consumer.h>

/*
* This is used to lock changes in serial line configuration.
@@ -3317,6 +3318,7 @@ 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 +3333,29 @@ int uart_get_rs485_mode(struct uart_port *port)
rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
}

+ if (port->rs485_term_gpio)
+ devm_gpiod_put(dev, port->rs485_term_gpio);
+
+ port->rs485_term_gpio = devm_gpiod_get(dev, "rs485-term",
+ GPIOD_FLAGS_BIT_DIR_OUT);
+ if (IS_ERR(port->rs485_term_gpio)) {
+ ret = PTR_ERR(port->rs485_term_gpio);
+ port->rs485_term_gpio = NULL;
+ if (ret != -ENOENT) {
+ if (ret != -EPROBE_DEFER)
+ dev_err(dev, "Cannot get rs485-term-gpios\n");
+ return ret;
+ }
+ } else {
+ ret = gpiod_get_value(port->rs485_term_gpio);
+ if (ret < 0) {
+ dev_err(dev, "Cannot get rs485-term-gpios value\n");
+ return ret;
+ }
+ if (ret)
+ rs485conf->flags |= SER_RS485_TERMINATE_BUS;
+ }
+
return 0;
}
EXPORT_SYMBOL_GPL(uart_get_rs485_mode);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index b649a2b894e7..9521e23b2144 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -251,6 +251,7 @@ 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 */
};
--
2.24.1
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