974e2f6a05
Exar devices like XR21B1411 can control an RS485 transceiver by automatically asserting the RTS#/RS485 pin before sending data and deasserting it when the last stop bit has been transmitted. The polarity of the RST#/RS485 signal is configurable and the hardware also supports half-duplex turn-around delay and address matching mode. Add support for enabling and disabling RS-485 mode and configuring the RST#/RS485 signal polarity using the TIOCGRS485 and TIOCSRS485 ioctls. Support for half-duplex turn-around delay and address matching mode are left unimplemented for now. User enables RS-485 mode by setting SER_RS485_ENABLED flag in struct serial_rs485 flags. User should also set either SER_RS485_RTS_ON_SEND or SER_RS485_RTS_AFTER_SEND to select the behaviour of the RTS#/RS485 pin. Setting SER_RS485_RTS_ON_SEND will drive RTS#/RS485 low during transmission. Signed-off-by: Jarkko Sonninen <kasper@iki.fi> [ johan: let SER_RS485_RTS_ON_SEND determine SER_RS485_RTS_AFTER_SEND ] Signed-off-by: Johan Hovold <johan@kernel.org>