Re: [PATCH v2 6/7] dt-bindings: iio: temperature: Add ADT7604 support to adi,ltc2983

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 14 May 2026 17:46:53 +0300
Liviu Stan <liviu.stan@analog.com> wrote:

> The ADT7604 shares the same die as the LTC2984. It repurposes the
> custom RTD sensor type (18) as a copper trace resistance sensor
> and the custom thermistor type (27) as a leak detector, and
> removes thermocouple, diode and direct ADC sensor types.
> 
> Add adi,adt7604 to the compatible list and introduce two new
> sensor node types specific to this device:
> 
> - copper-trace@: maps to the custom RTD sensor type (18). Two

Mixed back from Sashiko on this one...  But does point out that these
values are the hardware ones - binding shouldn't care as this
is using virtual ids to avoid reuse of existing ones.

Ignore it getting fussy about not matching hardware. We want them
to not match!


> variants: sub-ohm (< 1 ohm, adi,copper-trace-sub-ohm boolean,
> no custom table and excitation current) and standard (> 1 ohm,
> optional adi,custom-rtd table, optional excitation current
> defaulting to the datasheet recommended value). Primary output
> is resistance in ohms. When a custom table is provided, the
> chip also outputs temperature in millidegrees Celsius.
> 
> - leak-detector@: maps to the custom thermistor sensor type (27).
> Takes an optional adi,custom-leak-detector lookup table encoding
> resistance (uOhm) against coverage data. Primary output is
> resistance in ohms. When a custom table is provided, the chip
> also outputs coverage in percent.
> 
> Separate node types are used rather than extending the existing
> rtd@ and thermistor@ nodes because adi,custom-rtd and
> adi,custom-thermistor are currently required for types 18 and 27,
> and several properties (adi,number-of-wires, adi,rtd-curve,
> adi,rsense-share) have no meaning for copper trace and would need
> to be explicitly forbidden or ignored in the driver.
> 
> allOf conditions are added to restrict thermocouple, diode, direct
> ADC and active temperature nodes to non-ADT7604 devices, and to
> restrict copper-trace and leak-detector nodes to the ADT7604
> (some parts only).
> 
> Signed-off-by: Liviu Stan <liviu.stan@analog.com>


> +  '^leak-detector@':
> +    $ref: '#/$defs/sensor-node'
> +    unevaluatedProperties: false
> +    description: |
> +      Leak detector sensor (some parts only). Outputs resistance in ohms and,
> +      when a custom table is provided, a coverage percentage via
> +      IIO_COVERAGE_PERCENT (raw/1024 = coverage %).
> +
> +    properties:
> +      reg:
> +        minimum: 2
> +        maximum: 20
> +
> +      adi,sensor-type:
> +        description: Sensor type for leak detector sensors.
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +        const: 33
> +
> +      adi,rsense-handle:
> +        description: Associated sense resistor sensor.
> +        $ref: /schemas/types.yaml#/definitions/phandle
> +
> +      adi,excitation-current-nanoamp:
> +        description:
> +          Excitation current applied to the leak detector. The correct value
> +          depends on the electrical characteristics of the liquid being sensed.
> +          For example, 10000 (10µA) is recommended for PG25 (see datasheet
> +          Table 39).
> +        enum: [250, 500, 1000, 5000, 10000, 25000, 50000, 100000, 250000,
> +               500000, 1000000]
> +
> +      adi,custom-leak-detector:
> +        description: |
> +          Lookup table mapping resistance to coverage data. Entries must be
> +          in ascending resistance order. The coverage data field encodes the
> +          coverage percentage P as (P + 273.15) expressed in uK, i.e.
> +          (P * 1000000 + 273150000).

I like sashiko's comment on this.  Why are we having the hardware / driver
offset encoded in DT?  Just put in the value without the offset and apply that
in the driver.

> +        $ref: /schemas/types.yaml#/definitions/uint64-matrix
> +        minItems: 3
> +        maxItems: 64
> +        items:
> +          items:
> +            - description: Resistance point in uOhms.
> +            - description: Coverage data point (P + 273150000) in uK.
> +
> +    required:
> +      - adi,rsense-handle
> +      - adi,excitation-current-nanoamp
> +