On Sat, Dec 23, 2023 at 02:40:58PM +0100, Lino Sanfilippo wrote: > On 23.12.23 13:49, Christoph Niedermaier wrote: > > From: Lukas Wunner [mailto:lukas@xxxxxxxxx] > > Sent: Thursday, December 21, 2023 4:53 PM > > > Well why don't we just allow enabling or disabling RS-485 termination > > > independently from the SER_RS485_ENABLED bit in struct serial_rs485? > > > > > > Just let the user issue a TIOCSRS485 ioctl to toggle termination even > > > if in RS-232 mode and use that mode for RS-422. > > > > Sounds not bad. The termination should only depend on whether the GPIO is > > given or not. > > > > Irrespective of this, I think the Linos idea of an RS-422 mode is not bad. > > This allows you to take care of special features that were previously > > overlooked. For example, hardware flow control can be switched off so that > > this does not cause any problems. > > Also note, that RS232 and RS422 may NOT always be the same from driver > perspective. > Take a look at 8250_excar.c for example. That driver has to configure > the hardware accordingly when switching from RS232 to RS422 > (see iot2040_rs485_config()). Actually it seems there are a bunch of GPIOs on the IOT2040 board (called MPIO instead of GPIO by the driver). See the documentation of the wiring at line 87 in drivers/tty/serial/8250/8250_exar.c. So "configure the hardware" seems to just boil down to toggling the right GPIO (aka MPIO) pins to mux the UART signals to the right (RS232/RS485/RS422) transceiver. IOT2040 is an ACPI-based platform, so no devicetree to describe the RS232/RS485/RS422 mux GPIOs, but the underlying concept is the same. Thanks, Lukas
