Messages in this thread | | | Date | Wed, 15 Mar 2023 21:41:56 +0100 | From | Francesco Dolcini <> | Subject | Wrong RS485 RTS polarity in 8250 OMAP UART Driver vs DT binding? |
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Hello all, I have been recently working on RS485 on a TI K3 AM62 (using 8250_omap.c driver) and there is something that I do not really understand about the RTS polarity.
According to the DT binding (Documentation/devicetree/bindings/serial/rs485.yaml) when `rs485-rts-active-low` is present the behavior should be "drive RTS low when sending", however in the code it seems that this is handled the opposite way (drivers/tty/serial/8250/8250_omap.c:861).
/* * Retain same polarity semantics as RS485 software emulation, * i.e. SER_RS485_RTS_ON_SEND means driving RTS low on send. */
We have working hardware, using another UART that expect rs485-rts-active-low, and the exact same HW, when using OMAP uart, requires rs485-rts-active-high (the HW is modular, so we are really just changing the uart, keeping the same RS485 transceiver / connections).
What's going on there? Is the semantic of the 8250_omap driver just the opposite as it should be? Am I doing something wrong in the device tree?
This is the relevant DTS part.
&main_uart1 { linux,rs485-enabled-at-boot-time; rs485-rts-active-high; rs485-rx-during-tx; status = "okay"; };
Francesco
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