This patch provides an option to enable the RS485 mode at boot time
based on the state of a GPIO pin (DIP switch or configuration jumper).
The GPIO is defined by the device tree property "rs485-mode-gpio".
Signed-off-by: Tomas Paukrt <tomaspaukrt@xxxxxxxx>
---
Documentation/devicetree/bindings/serial/rs485.yaml | 4 ++++
drivers/tty/serial/serial_core.c | 12 ++++++++++++
2 files changed, 16 insertions(+)
diff --git a/Documentation/devicetree/bindings/serial/rs485.yaml b/Documentation/devicetree/bindings/serial/rs485.yaml
index 9418fd6..7a72f37 100644
--- a/Documentation/devicetree/bindings/serial/rs485.yaml
+++ b/Documentation/devicetree/bindings/serial/rs485.yaml
@@ -47,6 +47,10 @@ properties:
later with proper ioctl.
$ref: /schemas/types.yaml#/definitions/flag
+ rs485-mode-gpio:
+ description: GPIO pin to enable the RS485 mode at boot time.
+ maxItems: 1
+
rs485-rx-during-tx:
description: enables the receiving of data even while sending data.
$ref: /schemas/types.yaml#/definitions/flag
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index f1348a5..f1bf0b9 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3603,6 +3603,18 @@ int uart_get_rs485_mode(struct uart_port *port)
}
/*
+ * Enable the RS485 mode based on the state of a GPIO pin.
+ */
+ desc = devm_gpiod_get_optional(dev, "rs485-mode", GPIOD_IN);
+ if (IS_ERR(desc))
+ return dev_err_probe(dev, PTR_ERR(desc), "Cannot get rs485-mode-gpio\n");
+ if (desc) {
+ if (gpiod_get_value(desc))
+ rs485conf->flags |= SER_RS485_ENABLED;
+ devm_gpiod_put(dev, desc);
+ }
+
+ /*
* 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.
--
2.7.4
