diff options
| author | Lukas Wunner <lukas@wunner.de> | 2020-05-18 16:45:02 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-05-29 12:42:54 +0200 |
| commit | d58a2df3d8877b91ecbfb936a15da364251a228f (patch) | |
| tree | 3d4552397dddb3809888ba9094415ae7eac46239 | |
| parent | f40a6be4a4e4985aef5365007e2459d757f26bdd (diff) | |
serial: 8250: Support rs485 bus termination GPIO
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>
Link: https://lore.kernel.org/r/94c6c800d1ca9fa04766dd1d43a8272c5ad4bedd.1589811297.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/tty/serial/8250/8250_port.c | 3 | ||||
| -rw-r--r-- | drivers/tty/serial/serial_core.c | 16 | ||||
| -rw-r--r-- | include/linux/serial_core.h | 2 |
3 files changed, 21 insertions, 0 deletions
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index bf2722e5e3aa..1632f7d25acc 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -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. diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 43b6682877d5..57840cf90388 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -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); diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index b649a2b894e7..9fd550e7946a 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -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 */ }; |