Re: [PATCH v4 1/2] Add binding for ti,adc1018. It allows selection of channel as a Device Tree property

Jonathan Cameron
2022-01-09T11:11:37Z

On Fri, 31 Dec 2021 13:19:15 +0000
Iain Hunter <drhunter95@gmail.com> wrote:

> New binding file uses the adc.yaml to define channel selection
>
> Signed-off-by: Iain Hunter <drhunter95@gmail.com>
Hi Iain,

A few comments in addition to those Rob sent.
It's worth noting that there is a lot of 'history' in IIO bindings so
sometimes copying stuff from an existing binding is no longer the way
things should be done.

Jonathan

> ---
> .../bindings/iio/adc/ti,ads1018.yaml | 126 ++++++++++++++++++
> 1 file changed, 126 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,ads1018.yaml
>
> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1018.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1018.yaml
> new file mode 100644
> index 000000000000..a65fee9d83dd
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1018.yaml
> @@ -0,0 +1,126 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/ti,ads1018.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: TI ADS1018 4 channel I2C analog to digital converter
> +
> +maintainers:
> + - Iain Hunter <iain@hunterembedded.co.uk>
> +
> +description: |
> + Datasheet at: https://www.ti.com/lit/gpn/ads1018
> + Supports both single ended and differential channels.
> +
> +properties:
> + compatible:
> + const: ti,ads1018
> +
> + reg:
> + maxItems: 1
> +
> + "#address-cells":
> + const: 1
> +
> + "#size-cells":
> + const: 0
> +
> + "#io-channel-cells":
> + const: 1
> +
> + spi-max-frequency: true
> + spi-cpol: true
> + spi-cpha: true
> +
> +required:
> + - compatible
> + - reg
> + - "#address-cells"
> + - "#size-cells"
> + - spi-cpha
> +
> +additionalProperties: false
> +
> +patternProperties:
> + "^channel@([0-3])$":
> + $ref: "adc.yaml"
> + type: object
> +
> + properties:
> + reg:
> + description: |
> + Must be 0, actual channel selected in ti,adc-channels for single ended
> + or ti-adc-channels-diff for differential
> + $ref: /schemas/types.yaml#/definitions/uint32
> + enum: [0]

No. Should be some sort of index value. If I recall correctly, existing use is reg == channel
number when single ended and more loosely defined for differential. In many cases first of the
pair, but that's not always guaranteed to be unique (e.g. 0-1 and 0-3 in this case).

> +
> + ti,adc-channels:
> + description: |
> + List of single-ended channels muxed for this ADC. It can have up to 4
> + channels numbered 0-3

This is a new binding, so how can we have deprecated properties?
Also seems very odd indeed to have a list of channels defined inside a per channel node.

> + $ref: /schemas/types.yaml#/definitions/uint32-array
> + deprecated: true
> +
> + ti,adc-diff-channels:

Can this use diff-channels in the standard adc binding:
Documentation/devicetree/bindings/iio/adc/adc.yaml

> + description: |
> + List of differential channels muxed for this ADC between the pins vinp
> + and vinn. The 4 possible options are:
> + vinp=0, vinn=1
> + vinp=0, vinn=3
> + vinp=1, vinn=3
> + vinp=2, vinn=3
> +
> + They are listed in a pair <vinp vinn>.
> +
> + Note: At least one of "ti,adc-channels" or "ti,adc-diff-channels" is
> + required.
> + $ref: /schemas/types.yaml#/definitions/uint32-matrix
> + items:
> + items:
> + - description: |
> + "vinp" indicates positive input number
> + minimum: 0
> + maximum: 2
> + - description: |
> + "vinn" indicates negative input number
> + minimum: 1
> + maximum: 3

This should be a pair based constraint as not all options possible. Something like
oneOf:
- items:
- const: 0
- const: 1
- items:
- enum: [0, 1, 2]
- const: 3

> +
> +
> + required:
> + - reg
> +
> +examples:
> + - |
> + // example on SPI1 with single ended channel 1
> + spi {
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + adc@1 {
> + compatible = "ti,ads1018";
> + reg = <0x0>;
> + #address-cells = <1>;
> + #size-cells = <0>;
> + spi-cpha;
> + ti,adc-channels = <1>;

More recent approach to this is the one you've used for differential channels
- 1 child node per channel.

> + };
> + };
> + - |
> + // example on SPI0 with differential between inputs 0 and 3

The SPI0 vs 1 is correctly not part of this example, so drop that from
the comment.

> + spi {
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + adc@0 {
> + compatible = "ti,ads1018";
> + reg = <0x0>;
> + #address-cells = <1>;
> + #size-cells = <0>;
> + spi-cpha;
> + ti,adc-diff-channels = <0 3>;

This doesn't obey the schema you have above at all. Would looks something like
channel@0 {
diff-channels = <0 3>;
}

> + };
> + };
> +
> +...