RE: [PATCH v4 3/5] dt-bindings: iio: dac: Add adi,ltc2664.yaml

["Paller, Kim Seer" <KimSeer.Paller@xxxxxxxxxx>]

> -----Original Message-----
> From: David Lechner <dlechner@xxxxxxxxxxxx>
> Sent: Tuesday, June 25, 2024 12:49 AM
> To: Paller, Kim Seer <KimSeer.Paller@xxxxxxxxxx>; Conor Dooley
> <conor@xxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-iio@xxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; Jonathan Cameron <jic23@xxxxxxxxxx>; Lars-Peter
> Clausen <lars@xxxxxxxxxx>; Liam Girdwood <lgirdwood@xxxxxxxxx>; Mark
> Brown <broonie@xxxxxxxxxx>; Dimitri Fedrau <dima.fedrau@xxxxxxxxx>;
> Krzysztof Kozlowski <krzk+dt@xxxxxxxxxx>; Rob Herring <robh@xxxxxxxxxx>;
> Conor Dooley <conor+dt@xxxxxxxxxx>; Hennerich, Michael
> <Michael.Hennerich@xxxxxxxxxx>; Nuno Sá <noname.nuno@xxxxxxxxx>
> Subject: Re: [PATCH v4 3/5] dt-bindings: iio: dac: Add adi,ltc2664.yaml
> 
> [External]
> 
> 
> >>> +  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]
> >>
> >> Can you explain why this property is required, when below there's one that
> sets
> >> the ranges in microvolts? Isn't the only new information that this provides
> the
> >> reset values (in a few cases that it is not 0).
> >> What am I missing?
> >
> > For specifying output range and reset options without relying on software
> initialization
> > routines, and also for enabling the softspan feature, I think this property
> seems essential.
> 
> So in other words, this describes how the MSP pins are hardwired and
> the per-channel adi,output-range-microvolt is only permissible if
> 
> 	 adi,manual-span-operation-config = <7>;
> 
> (or omitted since 7 is the default)
> 
> because in that case each individual pin could have a different
> required range based on what is wire up to it?
> 
> But if adi,manual-span-operation-config is anything other than 7,
> then adi,output-range-microvolt should be not allowed since all
> channels will have the same range because of the hard-wired pins.
> 
> correct?

That's correct.
 
> The description could probably just be simplified to say that
> this describes how the 3 pins are hardwired and to see Table 4
> in the datasheet to understand the actual implications rather
> than reproducing that table here.
> 
> But I do agree that we need both properties. I think we are
> just missing:
> 
> - if:
>     properties:
>       adi,manual-span-operation-config:
>         const: 7
>   then:
>     patternProperties:
>       "^channel@[0-3]$":
>        adi,output-range-microvolt: false
> 
> (not tested - may need two ifs, one with
> 
> - if:
>     required:
>       - adi,manual-span-operation-config
>     properties:
>       adi,manual-span-operation-config:
>         const: 7
> 
> and one with
> 
> - if:
>     not:
>       required:
>         - adi,manual-span-operation-config
> 
> to make it work properly)
> 
> >
> >>> +    default: 7
> >>> +
> >>> +  io-channels:
> >>> +    description:
> >>> +      ADC channel to monitor voltages and temperature at the MUXOUT
> pin.
> >>> +    maxItems: 1
> >>> +
> >>> +  '#address-cells':
> >>> +    const: 1
> >>> +
> >>> +  '#size-cells':
> >>> +    const: 0
> >>> +
> >>> +patternProperties:
> >>> +  "^channel@[0-3]$":
> >>> +    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
> >>> +
> >>> +      adi,output-range-microvolt:
> >>> +        description: Specify the channel output full scale range.
> >>> +        oneOf:
> >>> +          - items:
> >>> +              - const: 0
> >>> +              - enum: [5000000, 10000000]
> >>> +          - items:
> >>> +              - const: -5000000
> >>> +              - const: 5000000
> >>> +          - items:
> >>> +              - const: -10000000
> >>> +              - const: 10000000
> >>> +          - items:
> >>> +              - const: -2500000
> >>> +              - const: 2500000
> >>> +
> >>> +    required:
> >>> +      - reg
> >>> +      - adi,output-range-microvolt
> 
> And adi,output-range-microvolt should not be required. When SoftSpan
> is not available (because MSP != 0x7), then the range is determined
> by adi,manual-span-operation-config.
> 
> And even when adi,manual-span-operation-config = <7>, there is still
> a default range, so adi,output-range-microvolt should still not be
> required in that case.

This makes sense how this operates. Appreciate the detailed feedback.