linux-kernel - Re: [PATCH v5 4/6] dt-bindings: iio: dac: Add adi,ltc2664.yaml

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Date: Tue, 2 Jul 2024 10:36:29 -0500
From: David Lechner <dlechner@...libre.com>
To: Kim Seer Paller <kimseer.paller@...log.com>,
 linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org
Cc: Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen
 <lars@...afoo.de>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, Dimitri Fedrau <dima.fedrau@...il.com>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Rob Herring <robh@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Michael Hennerich <michael.hennerich@...log.com>,
 Nuno Sá <noname.nuno@...il.com>
Subject: Re: [PATCH v5 4/6] dt-bindings: iio: dac: Add adi,ltc2664.yaml

On 7/1/24 10:00 PM, Kim Seer Paller wrote:
> Add documentation for ltc2664.
> 

...

> +  adi,manual-span-operation-config:
> +    description:
> +      This property must mimic the MSPAN pin configurations. By tying the MSPAN
> +      pins (MSP2, MSP1 and MSP0) to GND and/or VCC, any output range can be
> +      hardware-configured with different mid-scale or zero-scale reset options.
> +      The hardware configuration is latched during power on reset for proper
> +      operation.
> +        0 - MPS2=GND, MPS1=GND, MSP0=GND (+-10V, reset to 0V)
> +        1 - MPS2=GND, MPS1=GND, MSP0=VCC (+-5V, reset to 0V)
> +        2 - MPS2=GND, MPS1=VCC, MSP0=GND (+-2.5V, reset to 0V)
> +        3 - MPS2=GND, MPS1=VCC, MSP0=VCC (0V to 10, reset to 0V)
> +        4 - MPS2=VCC, MPS1=GND, MSP0=GND (0V to 10V, reset to 5V)
> +        5 - MPS2=VCC, MPS1=GND, MSP0=VCC (0V to 5V, reset to 0V)
> +        6 - MPS2=VCC, MPS1=VCC, MSP0=GND (0V to 5V, reset to 2.5V)
> +        7 - MPS2=VCC, MPS1=VCC, MSP0=VCC (0V to 5V, reset to 0V, enables SoftSpan)
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [0, 1, 2, 3, 4, 5, 6, 7]
> +    default: 7
> +
> +  io-channels:
> +    description:
> +      ADC channel to monitor voltages and temperature at the MUXOUT pin.
> +    maxItems: 1
> +
> +  '#address-cells':
> +    const: 1
> +
> +  '#size-cells':
> +    const: 0
> +
> +patternProperties:
> +  "^channel@[0-3]$":
> +    $ref: dac.yaml
> +    type: object
> +    additionalProperties: false
> +
> +    properties:
> +      reg:
> +        description: The channel number representing the DAC output channel.
> +        maximum: 3
> +
> +      adi,toggle-mode:
> +        description:
> +          Set the channel as a toggle enabled channel. Toggle operation enables
> +          fast switching of a DAC output between two different DAC codes without
> +          any SPI transaction.
> +        type: boolean
> +
> +      output-range-microvolt:

Could be helpful to add a description that says this property is only allowed when
SoftSpan is enabled rather than requiring people to reason through the logic.

> +        oneOf:
> +          - items:
> +              - const: 0
> +              - enum: [5000000, 10000000]
> +          - items:
> +              - const: -5000000
> +              - const: 5000000
> +          - items:
> +              - const: -10000000
> +              - const: 10000000
> +          - items:
> +              - const: -2500000
> +              - const: 2500000

           default: [0, 5000000]

> +
> +    required:
> +      - reg
> +
> +    allOf:
> +      - if:
> +          properties:
> +            adi,manual-span-operation-config:
> +              const: 7
> +        then:
> +          patternProperties:
> +            "^channel@[0-3]$":
> +              required: [output-range-microvolt]


This logic doesn't look right to me. If adi,manual-span-operation-config
is not 7, then SoftSpan is disabled, so we should have:

    output-range-microvolt: false

In that case since individual channels can't have a per-channel
configuration because SoftSpan is not enabled (unless I am misunderstanding
the datasheet?).

Also, output-range-microvolt should never be required, even when
adi,manual-span-operation-config is 7 because there is already a default
value range (0V to 5V) specified by the adi,manual-span-operation-config
property.

I think the correct logic would be:

    - if:
        not:
          properties:
            adi,manual-span-operation-config:
              const: 7
        then:
          patternProperties:
            "^channel@[0-3]$":
              properties:
                output-range-microvolt: false