linux-kernel - Re: [PATCH v5 3/6] dt-bindings: serial: add binding for rs485 rx-enable state when rs485 is disabled

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Message-ID: <20240130230220.GA2569797-robh@kernel.org>
Date: Tue, 30 Jan 2024 17:02:20 -0600
From: Rob Herring <robh@...nel.org>
To: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Heiko Stuebner <heiko@...ech.de>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org,
	quentin.schulz@...obroma-systems.com
Subject: Re: [PATCH v5 3/6] dt-bindings: serial: add binding for rs485
 rx-enable state when rs485 is disabled

On Fri, Jan 26, 2024 at 06:27:44PM +0100, Farouk Bouabid wrote:
> RS485 can have a receiver-enable gpio (rx-enable-gpios). When rs485 is

s/gpio/GPIO/

> enabled, this gpio, if provided, must be driven active while receiving.
> However when RS485 is disabled this gpio should not have an undefined
> state. In that case, as DE and RE pins can be connected both to this gpio,
> if its state is not properly defined, can cause unexpected transceiver
> behavior.
> This binding depend on rx-enable-gpios to be implemented.

Sounds like a constraint:

dependencies:
  rs485-rx-enable-inactive-when-rs485-disabled: [ rx-enable-gpios ]

> 
> Signed-off-by: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
> ---
>  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 b64577036b5c..4c79dfaaf460 100644
> --- a/Documentation/devicetree/bindings/serial/rs485.yaml
> +++ b/Documentation/devicetree/bindings/serial/rs485.yaml
> @@ -55,6 +55,11 @@ properties:
>      description: GPIO to handle a separate RS485 receive enable signal
>      maxItems: 1
>  
> +  rs485-rx-enable-inactive-when-rs485-disabled:

For something a bit shorter, perhaps: rs485-rx-enable-inactive-on-disable

> +    description: rx-enable GPIO is not active when RS485 is disabled. If missing, active-state
> +      is assumed.
> +    $ref: /schemas/types.yaml#/definitions/flag
> +
>    rs485-term-gpios:
>      description: GPIO pin to enable RS485 bus termination.
>      maxItems: 1
> 
> -- 
> 2.34.1
>