Re: [PATCH v8 1/2] dt-bindings: adc: add AD7173

[David Lechner <dlechner@xxxxxxxxxxxx>]

On Tue, Dec 12, 2023 at 11:45 AM Dumitru Ceclan <mitrutzceclan@xxxxxxxxx> wrote:
>
> The AD7173 family offer a complete integrated Sigma-Delta ADC solution
> which can be used in high precision, low noise single channel applications
> or higher speed multiplexed applications. The Sigma-Delta ADC is intended
> primarily for measurement of signals close to DC but also delivers
> outstanding performance with input bandwidths out to ~10kHz.

As stated in [1], we should try to make complete bindings. I think
more could be done here to make this more complete. Most notably, the
gpio-controller binding is missing. Also maybe something is needed to
describe how the SYNC/ERROR pin is wired up since it can be an input
or an output with different functions?

[1]: https://www.kernel.org/doc/html/latest/devicetree/bindings/writing-bindings.html

>
> Signed-off-by: Dumitru Ceclan <mitrutzceclan@xxxxxxxxx>
> ---
> V7->V8
>  - include missing fix from V6

Including the cumulative changelog for all revisions would be helpful
to reviewers who haven't been following closely.

>
>  .../bindings/iio/adc/adi,ad7173.yaml          | 170 ++++++++++++++++++
>  1 file changed, 170 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,ad7173.yaml
>
> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7173.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7173.yaml
> new file mode 100644
> index 000000000000..25a5404ee353
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7173.yaml
> @@ -0,0 +1,170 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +# Copyright 2023 Analog Devices Inc.
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/adi,ad7173.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Analog Devices AD7173 ADC
> +
> +maintainers:
> +  - Ceclan Dumitru <dumitru.ceclan@xxxxxxxxxx>
> +
> +description: |
> +  Bindings for the Analog Devices AD717X ADC's. Datasheets for supported chips:
> +    https://www.analog.com/media/en/technical-documentation/data-sheets/AD7172-2.pdf
> +    https://www.analog.com/media/en/technical-documentation/data-sheets/AD7173-8.pdf
> +    https://www.analog.com/media/en/technical-documentation/data-sheets/AD7175-2.pdf
> +    https://www.analog.com/media/en/technical-documentation/data-sheets/AD7176-2.pdf
> +
> +properties:
> +  compatible:
> +    enum:
> +      - adi,ad7172-2
> +      - adi,ad7173-8
> +      - adi,ad7175-2
> +      - adi,ad7176-2
> +
> +  reg:
> +    maxItems: 1
> +
> +  interrupts:
> +    maxItems: 1

Shouldn't this be 2? The datasheet says there is a "Data Output Ready"
signal on the DOUT/RDY pin and an "Error Output" on the SYNC/ERROR
pin. Although I could see how RDY could be considered part of the SPI
bus. In any case, a description explaining what the interrupt is would
be useful.

> +
> +  '#address-cells':
> +    const: 1
> +
> +  '#size-cells':
> +    const: 0
> +
> +  spi-max-frequency:
> +    maximum: 20000000
> +
> +  refin-supply:
> +    description: external reference supply, can be used as reference for conversion.
> +
> +  refin2-supply:
> +    description: external reference supply, can be used as reference for conversion.
> +
> +  avdd-supply:
> +    description: avdd supply, can be used as reference for conversion.

What about other supplies? AVDD1, AVDD2, IOVDD.


> +
> +patternProperties:
> +  "^channel@[0-9a-f]$":
> +    type: object
> +    $ref: adc.yaml
> +    unevaluatedProperties: false
> +
> +    properties:
> +      reg:
> +        minimum: 0
> +        maximum: 15
> +
> +      diff-channels:
> +        items:
> +          minimum: 0
> +          maximum: 31

Do we need to add overrides to limit the maximums for each compatible string?

> +
> +      adi,reference-select:
> +        description: |
> +          Select the reference source to use when converting on
> +          the specific channel. Valid values are:
> +          refin      : REFIN(+)/REFIN(−).
> +          refin2     : REFIN2(+)/REFIN2(−)
> +          refout-avss: REFOUT/AVSS (Internal reference)
> +          avdd       : AVDD
> +
> +          External reference refin2 only available on ad7173-8.
> +          If not specified, internal reference used.
> +        enum:
> +          - refin
> +          - refin2
> +          - refout-avss
> +          - avdd
> +        default: refout-avss

Missing string type?

> +
> +    required:
> +      - reg
> +      - diff-channels

Individual analog inputs can be used as single-ended or in pairs as
differential, right? If so, diff-channels should not be required to
allow for single-ended use.

And we would need to add something like a single-ended-channel
property to adc.yaml to allow mapping analog input pins to channels
similar to how diff-channels works, I think (I don't see anything like
that there already)?

So maybe something like:

oneOf:
  - required:
      single-ended-channel
  - required:
      diff-channels

> +
> +required:
> +  - compatible
> +  - reg
> +  - interrupts
> +
> +allOf:
> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +  - if:
> +      properties:
> +        compatible:
> +          not:
> +            contains:
> +              const: adi,ad7173-8
> +    then:
> +      properties:
> +        refin2-supply: false
> +      patternProperties:
> +        "^channel@[0-9a-f]$":
> +          properties:
> +            adi,reference-select:
> +              enum:
> +                - refin
> +                - refout-avss
> +                - avdd
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +    #include <dt-bindings/interrupt-controller/irq.h>
> +
> +    spi {
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +
> +      adc@0 {
> +        compatible = "adi,ad7173-8";
> +        reg = <0>;
> +
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        interrupts = <25 IRQ_TYPE_EDGE_FALLING>;
> +        interrupt-parent = <&gpio>;
> +        spi-max-frequency = <5000000>;
> +
> +        refin-supply = <&dummy_regulator>;
> +
> +        channel@0 {
> +          reg = <0>;
> +          bipolar;
> +          diff-channels = <0 1>;
> +          adi,reference-select = "refin";
> +        };
> +
> +        channel@1 {
> +          reg = <1>;
> +          diff-channels = <2 3>;
> +        };
> +
> +        channel@2 {
> +          reg = <2>;
> +          bipolar;
> +          diff-channels = <4 5>;
> +        };
> +
> +        channel@3 {
> +          reg = <3>;
> +          bipolar;
> +          diff-channels = <6 7>;
> +        };
> +
> +        channel@4 {
> +          reg = <4>;
> +          diff-channels = <8 9>;
> +          adi,reference-select = "avdd";
> +        };
> +      };
> +    };
> --
> 2.42.0
>
>