On 21/11/2023 09:27, Rasmus Villemoes wrote: > On 21/11/2023 08.52, Krzysztof Kozlowski wrote: >> On 20/11/2023 16:10, Rasmus Villemoes wrote: >>> Some boards are capable of both rs232 and rs485, and control which >>> external terminals are active via a gpio-controlled mux. Allow >>> describing that gpio in DT so that the kernel can transparently handle >>> the proper setting when the uart is switched between rs232 and rs485 >>> modes. >>> >>> Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> >>> --- >>> Documentation/devicetree/bindings/serial/rs485.yaml | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/Documentation/devicetree/bindings/serial/rs485.yaml b/Documentation/devicetree/bindings/serial/rs485.yaml >>> index 9418fd66a8e9..e8136c7d22ed 100644 >>> --- a/Documentation/devicetree/bindings/serial/rs485.yaml >>> +++ b/Documentation/devicetree/bindings/serial/rs485.yaml >>> @@ -61,6 +61,11 @@ properties: >>> the active state enables RX during TX. >>> maxItems: 1 >>> >>> + rs485-mux-gpios: >>> + description: GPIO pin to control muxing of the SOC signals to the RS485 >>> + transceiver. >>> + maxItems: 1 >> >> Aren't you duplicating >> https://lore.kernel.org/all/3Nk.ZZrp.5w3Yn0Ecy5C.1bMzDp@xxxxxxxxx/ ? > > Hadn't seen that, but no, this is not at all the same. That patch seems > to define an input pin to tell whether to enable rs485 mode or not (sort > of early run-time version of the linux,rs485-enabled-at-boot-time). > >> Anyway, similar comments: this does not look like generic RS485 >> property. Are you saying that standard defines such GPIO? > > No, I'm saying that several boards that exist in the wild have the > RX/TX/CTS etc. pins routed to a multiplexer, which in turn routes those > signals to either a rs485 transceiver or an rs232 driver (and those in > turn are connected to different screw terminals). So no, it's not a > property of the rs485 protocol itself, but very much related to making > use of rs485 (and rs232, though of course not simultaneously) on such > boards. Which upstream boards use it? To me it looks like specific to each controller, not to RS485. > > Would a link to a schematic help? Yes, always :) Best regards, Krzysztof
