@@ -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.
@@ -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);
@@ -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 */
};
Commit e8759ad17d41 ("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: Lukas Wunner <lukas@wunner.de> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Jan Kiszka <jan.kiszka@siemens.com> --- drivers/tty/serial/8250/8250_port.c | 3 +++ drivers/tty/serial/serial_core.c | 16 ++++++++++++++++ include/linux/serial_core.h | 2 ++ 3 files changed, 21 insertions(+)