Re: [PATCH v4 02/10] dt-bindings: iio: adc: support the TI ADS126x ADC family

["Kurt Borja" <kuurtb@gmail.com>]

On Sat Aug 29, 2026 at 10:53 PM -03, Jonathan Cameron wrote:
> On Fri, 28 Aug 2026 01:38:17 -0500
> Kurt Borja <kuurtb@gmail.com> wrote:
>
>> The ADS1262 and ADS1263 are 32-bit, 38.4-kSPS delta-sigma ADCs with an
>> integrated PGA, internal reference, excitation and burn-out current
>> sources for sensor biasing and diagnostics. The ADS1263 is compatible
>> with ADS1262, but includes a second auxiliary ADC (ADC2) to perform main
>> channel (ADC1) cross-checking measurements, system background
>> measurements, or temperature compensation of the primary sensor.
>> 
>> Both parts can configure per-channel voltage reference source,
>> excitation current sources (IDAC), plus input and IDAC chopping for
>> offset and IDAC mismatch cancellation. This lets the device drive and
>> ratiometrically measure RTDs and other resistive sensors.
>> 
>> Signed-off-by: Kurt Borja <kuurtb@gmail.com>
> A few queries in here from me.
>
> Jonathan
>
>> ---
>>  .../devicetree/bindings/iio/adc/ti,ads1262.yaml    | 376 +++++++++++++++++++++
>>  MAINTAINERS                                        |   6 +
>>  2 files changed, 382 insertions(+)
>> 
>> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1262.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1262.yaml
>> new file mode 100644
>> index 000000000000..7e26572388e4
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1262.yaml
>
>> +  '#io-channel-cells':
>> +    minimum: 1
>> +    maximum: 2
>> +    description: |
>> +      The first cell selects the channel by its reg. The second cell selects
>> +      between the main ADC (ADC1) and the auxiliary ADC (ADC2) as follows:
>> +        0: ADC1
>> +        1: ADC2
>
> This one is odd enough I wonder if we just say it is always 2 and that
> for the parts with out an ADC2 the value of the selector cell can only be
> 0. Also, does this ordering make sense?  Maybe pick the ADC with first
> parameter is more natural?

I agree. I think its simpler to just 'const: 2' and validate its value.

>
>> +
>> +  '#gpio-cells':
>> +    const: 2
>
>> +patternProperties:
>
> ...
>
>> +      reference-sources:
>> +        minItems: 2
>> +        description:
>> +          Indicates the reference sources for this channel. The first and second
>> +          items are the positive (REFP) and negative (REFN) sources of the main
>> +          ADC (ADC1). The third item is the reference source of the secondary
>> +          ADC (ADC2) and must always have a positive differential voltage.
>
> I think it would be good to illustrate the 2 only case in the first example.
>
>> +        items:
>> +          - enum: [internal-p, refp1, refp2, refp3, avdd]
>> +          - enum: [internal-n, refn1, refn2, refn3, avss]
>> +          - enum: [internal, refp1-refn1, refp2-refn2, refp3-refn3, avdd-avss]
>> +
>> +      ti,reference-reversal:
>> +        $ref: /schemas/types.yaml#/definitions/flag
>> +        description:
>> +          Indicates that the ADC1 (this has no effect on ADC2) reference voltage
>> +          for this channel has negative polarity and thus should be internally
>> +          reversed.
>> +
>> +      excitation-channels:
>> +        minItems: 1
>> +        maxItems: 2
>> +        description:
>> +          Selects the pins for the IDAC sources from 0 (AIN0) to 10 (AINCOM).
>> +          The first value corresponds to IDAC1 and the second to IDAC2.
>> +        items:
>> +          minimum: 0
>> +          maximum: 10
>
> Why do we allow configurations with just IADC1 (minItems: 1) but not those
> with just IADC2?

Hmm I think we can get way with this for simplicity. Both IDACs are
electrically equivalent so if only one is provided there shouldn't be a
problem? I'll try to think about potential issues with this reasoning
before v5.

>
>> +
>> +      excitation-current-nanoamp:
>> +        minItems: 1
>> +        maxItems: 2
>> +        description:
>> +          The first value corresponds to IDAC1 and the second to IDAC2.
>> +        items:
>> +          enum: [50000, 100000, 250000, 500000, 750000, 1000000, 1500000,
>> +                 2000000, 2500000, 3000000]
>> +
>> +      excitation-current-chopping: true
>
>> +allOf:
>> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
>> +  - if:
>> +      properties:
>> +        compatible:
>> +          contains:
>> +            const: ti,ads1263
>> +    then:
>> +      properties:
>> +        '#io-channel-cells':
>> +          minimum: 1
>> +          maximum: 2
>> +      patternProperties:
>> +        "^channel@[0-9]+$":
>> +          properties:
>> +            reference-sources:
>> +              minItems: 3
>> +              maxItems: 3
>> +              default: [internal-p, internal-n, internal]
>> +    else:
>> +      properties:
>> +        '#io-channel-cells':
>> +          const: 1
>> +      patternProperties:
>> +        "^channel@[0-9]+$":
>> +          properties:
>> +            reference-sources:
>> +              minItems: 2
>> +              maxItems: 2
>> +              default: [internal-p, internal-n]
>> +
>> +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 = "ti,ads1262";
>> +            reg = <0>;
>> +            spi-max-frequency = <8000000>;
>> +            spi-cpha;
>> +            avdd-supply = <&avdd>;
>> +            dvdd-supply = <&dvdd>;
>> +            #address-cells = <1>;
>> +            #size-cells = <0>;
>> +
>> +            interrupts-extended = <&gpio 0 IRQ_TYPE_EDGE_FALLING>;
>> +            interrupt-names = "drdy";
>> +
>> +            /* Typical common mode voltage configuration */
>> +            aincom-supply = <&ads1262_vbias>;
>> +
>> +            regulators {
>> +                ads1262_vbias: vbias { };
>> +            };
>> +
>> +            channel@0 {
>> +                reg = <0>;
>> +                single-channel = <0>;
>> +                /* The VBIAS is enabled on pin 10 (AINCOM) */
>> +                common-mode-channel = <10>;
>
> As above, I'd like a dual reference source example usage on
> a channel here.

Sure!

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

-- 
Thanks,
 ~ Kurt