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Tue, 21 Nov 2023 00:34:04 -0800 (PST) Received: from [192.168.1.20] ([178.197.222.11]) by smtp.gmail.com with ESMTPSA id s5-20020a5d6a85000000b0032d9f32b96csm13765372wru.62.2023.11.21.00.34.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Nov 2023 00:34:03 -0800 (PST) Message-ID: <67a2cea0-f2de-4e7d-bc9d-ae29885f9210@linaro.org> Date: Tue, 21 Nov 2023 09:34:02 +0100 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] dt-bindings: serial: rs485: add rs485-mux-gpios binding Content-Language: en-US To: Rasmus Villemoes , Greg Kroah-Hartman , Jiri Slaby , Rob Herring , Krzysztof Kozlowski , Conor Dooley Cc: devicetree@vger.kernel.org, Andy Shevchenko , Lukas Wunner , Rob Herring , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org References: <20231120151056.148450-1-linux@rasmusvillemoes.dk> <20231120151056.148450-2-linux@rasmusvillemoes.dk> <1c016987-da88-47f2-bc1b-fcbe4c71a5c9@rasmusvillemoes.dk> From: Krzysztof Kozlowski Autocrypt: addr=krzysztof.kozlowski@linaro.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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 >>> --- >>> 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@seznam.cz/ ? > > 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