Re: [PATCH v2 1/2] dt-bindings: iio: temperature: add support for MCP998X

[Conor Dooley <conor@kernel.org>]

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On Thu, May 29, 2025 at 01:13:38PM -0500, David Lechner wrote:
> On 5/29/25 4:36 AM, victor.duicu@microchip.com wrote:
> > From: Victor Duicu <victor.duicu@microchip.com>
> > 
> > This is the devicetree schema for Microchip MCP998X/33 and
> > MCP998XD/33D Multichannel Automotive Temperature Monitor Family.
> > 
> > Signed-off-by: Victor Duicu <victor.duicu@microchip.com>
> > ---
> >  .../iio/temperature/microchip,mcp9982.yaml    | 174 ++++++++++++++++++
> >  1 file changed, 174 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/iio/temperature/microchip,mcp9982.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9982.yaml b/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9982.yaml
> > new file mode 100644
> > index 000000000000..249470c8953b
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iio/temperature/microchip,mcp9982.yaml
> > @@ -0,0 +1,174 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/iio/temperature/microchip,mcp9982.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Microchip MCP998X/33 and MCP998XD/33D Multichannel Automotive
> > +       Temperature Monitor Family
> > +
> > +maintainers:
> > +  - Victor Duicu <victor.duicu@microchip.com>
> > +
> > +description: |
> > +  The MCP998X/33 and MCP998XD/33D family is a high-accuracy 2-wire multichannel
> > +  automotive temperature monitor.
> > +  The datasheet can be found here:
> > +    https://ww1.microchip.com/downloads/aemDocuments/documents/MSLD/ProductDocuments/DataSheets/MCP998X-Family-Data-Sheet-DS20006827.pdf
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - microchip,mcp9933
> > +      - microchip,mcp9933d
> > +      - microchip,mcp9982
> > +      - microchip,mcp9982d
> > +      - microchip,mcp9983
> > +      - microchip,mcp9983d
> > +      - microchip,mcp9984
> > +      - microchip,mcp9984d
> > +      - microchip,mcp9985
> > +      - microchip,mcp9985d
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +    maxItems: 2
> > +
> > +  interrupt-names:
> > +    description:
> > +      alert1 indicates a HIGH or LOW limit was exceeded.
> > +      alert2 indicates a THERM limit was exceeded.
> 
> I think we need minItems: 1 here.
> 
> > +    items:
> > +      - const: alert1
> > +      - const: alert2
> 
> Typically, interrupts are named after the pin they are wired to, not
> the signal. This is especially true when a single pin can be configured
> for different signals as is the case here.
> 
> There is a /ALERT//THERM pin on all chips and a /THERM//ADDR pin on some
> chips.
> 
> So I would expect the names to match that:
> 
>     items:
>       - const: alert-therm
>       - const: therm-addr
> 
> And then extra descriptions probably aren't needed.
> 
> If we want to be extra careful, we could also add an -if: below to set
> maxItems: 1 for interrupts and interrupt-names on chips that only have
> the one pin.
> 
> And I assume that the /SYS_SHDN pin would never be wired up as an interrupt?
> 
> > +
> > +  "#address-cells":
> > +    const: 1
> > +
> > +  "#size-cells":
> > +    const: 0
> > +
> > +  microchip,apdd-state:
> > +    description:
> > +      Enable anti-parallel diode mode operation.
> > +      MCP9984/84D/85/85D and MCP9933/33D support reading two external diodes
> > +      in anti-parallel connection on the same set of pins.
> > +      Omit this tag to disable anti-parallel diode mode.
> > +    type: boolean
> > +
> > +  microchip,recd12:
> > +    description:
> > +      Enable resistance error correction for external channels 1 and 2.
> > +      Omit this tag to disable REC for channels 1 and 2.
> > +    type: boolean
> > +
> > +  microchip,recd34:
> > +    description:
> > +      Enable resistance error correction for external channels 3 and 4.
> > +      Omit this tag to disable REC for channels 3 and 4.

Why are these two devicetree properties, rather than runtime controls?

> > +    type: boolean
> > +
> > +  label:
> > +    description: Unique name to identify which device this is.
> > +
> > +  vdd-supply: true
> > +
> > +patternProperties:
> > +  "^channel@[1-4]$":
> > +    description:
> > +      Represents the external temperature channels to which
> > +      a remote diode is connected.
> > +    type: object
> > +
> > +    properties:
> > +      reg:
> > +        items:
> > +          minimum: 1
> > +          maximum: 4
> > +
> > +      microchip,ideality-factor:
> > +        description:
> > +          Each channel has an ideality factor.
> > +          Beta compensation and resistance error correction automatically
> > +          correct for most ideality errors. So ideality factor does not need
> > +          to be adjusted in general.
> > +          Omit this tag in order to set the default value.
> > +        $ref: /schemas/types.yaml#/definitions/uint32
> > +        default: 18
> > +
> > +      label:
> > +        description: Unique name to identify which channel this is.
> > +
> > +    required:
> > +      - reg
> > +
> > +    additionalProperties: false
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - vdd-supply
> > +
> > +allOf:
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            enum:
> > +              - microchip,mcp9982
> > +              - microchip,mcp9982d
> > +              - microchip,mcp9983
> > +              - microchip,mcp9983d
> > +    then:
> > +      properties:
> > +        microchip,apdd-state: false
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            enum:
> > +              - microchip,mcp9982
> > +              - microchip,mcp9982d
> > +              - microchip,mcp9933
> > +              - microchip,mcp9933d
> > +    then:
> > +      properties:
> > +        microchip,recd34: false
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    i2c {
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        temperature-sensor@4c {
> > +            compatible = "microchip,mcp9985";
> > +            reg = <0x4c>;
> > +
> > +            #address-cells = <1>;
> > +            #size-cells = <0>;
> > +
> > +            label = "temperature-sensor";
> 
> This is the same as the node name, so probably not the best
> example of a label.

Ye, I'm not convinced this property has any value, when the channels
themselves can have labels.

> 
> > +
> > +            microchip,apdd-state;
> > +            microchip,recd12;
> > +            microchip,recd34;
> > +            vdd-supply = <&vdd>;
> > +
> > +            channel@1 {
> > +                reg = <0x1>;
> 
> Why 0x here?
> 
> > +                label = "CPU Temperature";
> > +            };
> > +
> > +            channel@2 {
> > +                reg = <0x2>;
> > +                label = "GPU Temperature";
> > +            };
> > +        };
> > +    };
> > +
> > +...
> 

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