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

Paller, Kim Seer
2024-06-25T15:42:19Z

> -----Original Message-----
> From: David Lechner <dlechner@baylibre.com>
> Sent: Tuesday, June 25, 2024 12:49 AM
> To: Paller, Kim Seer <KimSeer.Paller@analog.com>; Conor Dooley
> <conor@kernel.org>
> Cc: linux-kernel@vger.kernel.org; linux-iio@vger.kernel.org;
> devicetree@vger.kernel.org; Jonathan Cameron <jic23@kernel.org>; Lars-Peter
> Clausen <lars@metafoo.de>; Liam Girdwood <lgirdwood@gmail.com>; Mark
> Brown <broonie@kernel.org>; Dimitri Fedrau <dima.fedrau@gmail.com>;
> Krzysztof Kozlowski <krzk+dt@kernel.org>; Rob Herring <robh@kernel.org>;
> Conor Dooley <conor+dt@kernel.org>; Hennerich, Michael
> <Michael.Hennerich@analog.com>; Nuno Sá <noname.nuno@gmail.com>
> 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.