linux-kernel - Re: [PATCH 1/2] dt-bindings: iio: adc: Add binding for AD7380 ADCs

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Date:   Sun, 10 Dec 2023 13:49:32 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     David Lechner <dlechner@...libre.com>
Cc:     linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Michael Hennerich <michael.hennerich@...log.com>,
        Nuno Sá <nuno.sa@...log.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: iio: adc: Add binding for AD7380 ADCs

On Fri,  8 Dec 2023 09:51:40 -0600
David Lechner <dlechner@...libre.com> wrote:

> This adds a binding specification for the Analog Devices Inc. AD7380
> family of ADCs.
> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
Hi David,

Comments inline.  A question for Mark Brown on the 2-wire bit..
Do we have existing DT bindings for devices with parallel spi data
outputs?

> ---
>  .../devicetree/bindings/iio/adc/adi,ad7380.yaml    | 102 +++++++++++++++++++++
>  MAINTAINERS                                        |   9 ++
>  2 files changed, 111 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml
> new file mode 100644
> index 000000000000..e9a0b72cd9d3
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml
...


> +  * https://www.analog.com/en/products/ad7380.html
> +  * https://www.analog.com/en/products/ad7381.html
> +  * https://www.analog.com/en/products/ad7383.html
> +  * https://www.analog.com/en/products/ad7384.html

> +  adi,sdo-mode:
> +    $ref: /schemas/types.yaml#/definitions/string
> +    enum: [ 1-wire, 2-wire ]
> +    description:
> +      In 1-wire mode, the SDOA pin acts as the sole data line and the SDOB/ALERT
> +      pin acts as the ALERT interrupt signal. In 2-wire mode, data for input A
> +      is read from SDOA and data for input B is read from SDOB/ALERT (and the
> +      ALERT interrupt signal is not available).

This is fun...  If I understand correctly 2-wire requires two SPI buses (or a complex
spi controller that does parallel serial channels).  What would description for that
look like in DT and can we not establish what is wanted here from that bus description
rather than an adi specific property?

Seems a bit like parallel-memories.

Mark, any insights into what we should do to describe this?

> +
> +  vcc-supply:
> +    description: A 3V to 3.6V supply that powers the chip.
> +
> +  vlogic-supply:
> +    description:
> +      A 1.65V to 3.6V supply for the logic pins.
> +
> +  refio-supply:
> +    description:
> +      A 2.5V to 3.3V supply for the external reference voltage. When omitted,
> +      the internal 2.5V reference is used.
> +
> +  interrupts:
> +    description:
> +      When the device is using 1-wire mode, this property is used to optionally
> +      specify the ALERT interrupt.
> +    maxItems: 1
> +
> +required:
> +  - compatible
> +  - reg
> +  - adi,sdo-mode

Could define a default of 1-wire?  Simplifies things a little in the bindings.

> +  - vcc-supply
> +  - vlogic-supply