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

From: David Lechner
Date: Tue Dec 12 2023 - 10:10:13 EST

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
>
>