linux-kernel - Re: [PATCH v2 2/8] dt-bindings: iio: dac: maxim,ds4424: add maxim,rfs-ohms property

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Message-ID: <20260127-consonant-vividness-13707c7cf8f6@spud>
Date: Tue, 27 Jan 2026 19:49:20 +0000
From: Conor Dooley <conor@...nel.org>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	David Jander <david@...tonic.nl>
Subject: Re: [PATCH v2 2/8] dt-bindings: iio: dac: maxim,ds4424: add
 maxim,rfs-ohms property

On Tue, Jan 27, 2026 at 07:09:33AM +0100, Oleksij Rempel wrote:
> The Maxim DS4422/DS4424 and DS4402/DS4404 current DACs determine their
> full-scale output current via external resistors (Rfs) connected to the
> FSx pins. Without knowing these values, the full-scale range of the
> hardware is undefined.
> 
> Add the 'maxim,rfs-ohms' property to describe these physical components.
> This property is required to provide a complete description of the
> hardware configuration.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> ---
> changes v2:
> - make maxim,rfs-ohms a required property as the hardware range is undefined
>   without external resistors.
> - add allOf constraints to enforce 2 vs 4 items in maxim,rfs-ohms based on
>   compatible string.
> - drop explicit $ref for maxim,rfs-ohms to fix dt_binding_check warning.
> - update example in binding to include the new required property.
> ---
>  .../bindings/iio/dac/maxim,ds4424.yaml        | 36 +++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml b/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
> index efe63e6cb55d..400afd8771aa 100644
> --- a/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
> +++ b/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
> @@ -27,9 +27,44 @@ properties:
>  
>    vcc-supply: true
>  
> +  maxim,rfs-ohms:
> +    description: |
> +      Array of resistance values in Ohms for the external Rfs resistors
> +      connected to the FS pins.
> +      - For DS44x2 (2 channels): 2 values required.
> +      - For DS44x4 (4 channels): 4 values required.
> +      Typical values range from 40000 (40 kOhm) to 160000 (160 kOhm).

Add here
maxItems: 4
minItems: 2

Are 40kOhm and 160kOhm actual max/min values, or just a suggested range?

> +
>  required:
>    - compatible
>    - reg
> +  - maxim,rfs-ohms
> +
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - maxim,ds4402
> +              - maxim,ds4422
> +    then:
> +      properties:
> +        maxim,rfs-ohms:

> +          minItems: 2

Remove this...

> +          maxItems: 2
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - maxim,ds4404
> +              - maxim,ds4424
> +    then:
> +      properties:
> +        maxim,rfs-ohms:
> +          minItems: 4


> +          maxItems: 4

...and this. The outer-most constraints should be in the definition and
the if/else bit just adjusts whichever bounds it needs to.

Cheers,
Conor.

pw-bot: changes-requested

>  
>  additionalProperties: false
>  
> @@ -43,6 +78,7 @@ examples:
>              compatible = "maxim,ds4424";
>              reg = <0x10>; /* When A0, A1 pins are ground */
>              vcc-supply = <&vcc_3v3>;
> +            maxim,rfs-ohms = <5100>, <5100>, <5100>, <5100>;
>          };
>      };
>  ...
> -- 
> 2.47.3
> 

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