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Date: Tue, 21 Nov 2023 09:28:10 +0100 (CET) From: "Tomas Paukrt" <tomaspaukrt@...il.cz> To: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Jiri Slaby" <jirislaby@...nel.org>, "Rob Herring" <robh+dt@...nel.org>, "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>, "Conor Dooley" <conor+dt@...nel.org> Cc: <linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>, <devicetree@...r.kernel.org> Subject: [PATCH v4 1/2] serial: core: Add support for enabling RS485 mode via GPIO at boot time Add 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 "linux,rs485-mode-gpio". Signed-off-by: Tomas Paukrt <tomaspaukrt@...il.cz> --- drivers/tty/serial/serial_core.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) 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, "linux,rs485-mode", GPIOD_IN); + if (IS_ERR(desc)) + return dev_err_probe(dev, PTR_ERR(desc), "Cannot get linux,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
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