On Thu, Nov 23, 2023 at 11:07:16AM +0100, Rasmus Villemoes wrote: > On 22/11/2023 15.53, Lukas Wunner wrote: > > But if that patch gets accepted, we'd have *three* different modes: > > RS-232, RS-485, RS-422. A single GPIO seems insufficient to handle that. > > You'd need at least two GPIOs. > > I don't see Crescent introducing any new gpio that needs to be handled. > In fact, I can't even see why from the perspective of the software that > rs422 isn't just rs232; there's no transmit enable pin that needs to be > handled. But maybe the uart driver does something different in rs422 > mode; I assume he must have some update of some driver, since otherwise > the new rs422 bit should be rejected by the core. So I can't really see > the whole picture of that rs422 story. The question is, could we conceivably have the need to support switching between the three modes RS-232, RS-485, RS-422. If yes, then the GPIO mux interface should probably allow for that. As a case in point, the Siemens IOT 2040 has two serial ports which can be set to either of those three modes. The signals are routed to the same D-sub socket, but the pins used are different. See page 46 and 47 of this document: https://cache.industry.siemens.com/dl/files/658/109741658/att_899623/v1/iot2000_operating_instructions_enUS_en-US.pdf The driver for this product is 8250_exar.c. It's an Intel-based product, so no devicetree, but it shows that such use cases exist. Thanks, Lukas
