linux-kernel - Re: [PATCH v2 3/4] dt-bindings: iio: adc: ad4080: add AD4880 support

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Message-ID: <20260207-evasive-mastodon-of-apotheosis-e663a1@quoll>
Date: Sat, 7 Feb 2026 11:41:45 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Antoniu Miclaus <antoniu.miclaus@...log.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, 
	Michael Hennerich <Michael.Hennerich@...log.com>, Jonathan Cameron <jic23@...nel.org>, 
	David Lechner <dlechner@...libre.com>, Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Olivier Moysan <olivier.moysan@...s.st.com>, Mark Brown <broonie@...nel.org>, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH v2 3/4] dt-bindings: iio: adc: ad4080: add AD4880 support

On Fri, Feb 06, 2026 at 06:07:15PM +0200, Antoniu Miclaus wrote:
> Add support for the AD4880, a dual-channel 20-bit 40MSPS SAR ADC
> with integrated fully differential amplifiers (FDA).
> 
> The AD4880 has two independent ADC channels, each with its own SPI
> configuration interface. This requires:
> - Two entries in reg property for primary and secondary channel chip selects

Please wrap commit message according to Linux coding style / submission
process (neither too early nor over the limit):
https://elixir.bootlin.com/linux/v6.4-rc1/source/Documentation/process/submitting-patches.rst#L597

Please run scripts/checkpatch.pl on the patches and fix reported
warnings.

> - Two io-backends entries for the two data channels
> 
> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
> ---
> Changes in v2:
>   - Replace custom adi,aux-spi-cs property with standard reg property
>     containing two entries for multi-channel devices
>   - Add conditional schema validation for reg and io-backends based on
>     compatible string
>   - Update example to use reg = <0 1> instead of adi,aux-spi-cs
>   - Add AD4880 datasheet link
> 
>  .../bindings/iio/adc/adi,ad4080.yaml          | 51 ++++++++++++++++++-
>  1 file changed, 49 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> index ccd6a0ac1539..7108a91bb0bf 100644
> --- a/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml
> @@ -18,7 +18,11 @@ description: |
>    service a wide variety of precision, wide bandwidth data acquisition
>    applications.
>  
> +  The AD4880 is a dual-channel variant with two independent ADC channels,
> +  each with its own SPI configuration interface.
> +
>    https://www.analog.com/media/en/technical-documentation/data-sheets/ad4080.pdf
> +  https://www.analog.com/media/en/technical-documentation/data-sheets/ad4880.pdf
>  
>  $ref: /schemas/spi/spi-peripheral-props.yaml#
>  
> @@ -31,9 +35,15 @@ properties:
>        - adi,ad4084
>        - adi,ad4086
>        - adi,ad4087
> +      - adi,ad4880
>  
>    reg:
> -    maxItems: 1
> +    minItems: 1
> +    maxItems: 2
> +    description:
> +      SPI chip select(s). For single-channel devices, one chip select.
> +      For multi-channel devices like AD4880, two chip selects are required
> +      as each channel has its own SPI configuration interface.
>  
>    spi-max-frequency:
>      description: Configuration of the SPI bus.
> @@ -57,7 +67,8 @@ properties:
>    vrefin-supply: true
>  
>    io-backends:
> -    maxItems: 1
> +    minItems: 1
> +    maxItems: 2

Instead list the items with minItems, so the order is defined.

>  
>    adi,lvds-cnv-enable:
>      description: Enable the LVDS signal type on the CNV pin. Default is CMOS.
> @@ -78,6 +89,25 @@ required:
>    - vdd33-supply
>    - vrefin-supply
>  
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            const: adi,ad4880
> +    then:
> +      properties:
> +        reg:
> +          minItems: 2
> +        io-backends:
> +          minItems: 2
> +    else:
> +      properties:
> +        reg:
> +          maxItems: 1
> +        io-backends:
> +          maxItems: 1
> +
>  additionalProperties: false
>  
>  examples:
> @@ -98,4 +128,21 @@ examples:
>            io-backends = <&iio_backend>;
>          };
>      };
> +  - |
> +    spi {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@0 {
> +          compatible = "adi,ad4880";
> +          reg = <0 1>;

<0>, <1>, no? You want two separate chip selects, right? (size-cells is
0).

Best regards,
Krzysztof