RE: [PATCH v2 3/3] dt-bindings: iio: Add ltc2688 documentation

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> -----Original Message-----
> From: Jonathan Cameron <jic23@xxxxxxxxxx>
> Sent: Sunday, January 16, 2022 1:02 PM
> To: Sa, Nuno <Nuno.Sa@xxxxxxxxxx>
> Cc: linux-iio@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; Rob
> Herring <robh+dt@xxxxxxxxxx>; Lars-Peter Clausen
> <lars@xxxxxxxxxx>; Hennerich, Michael
> <Michael.Hennerich@xxxxxxxxxx>
> Subject: Re: [PATCH v2 3/3] dt-bindings: iio: Add ltc2688
> documentation
> 
> [External]
> 
> On Sat, 15 Jan 2022 10:27:05 +0100
> Nuno Sá <nuno.sa@xxxxxxxxxx> wrote:
> 
> > Document the LTC2688 devicetree properties.
> >
> > Signed-off-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
> Hi Nuno,
> 
> A few minor comments inline.  I've reviewed this first so might
> find answers to some of them when reading the driver code.
> 
> Thanks,
> 
> Jonathan
> 
> > ---
> >  .../bindings/iio/dac/adi,ltc2688.yaml         | 147
> ++++++++++++++++++
> >  MAINTAINERS                                   |   1 +
> >  2 files changed, 148 insertions(+)
> >  create mode 100644
> Documentation/devicetree/bindings/iio/dac/adi,ltc2688.yaml
> >
> > diff --git
> a/Documentation/devicetree/bindings/iio/dac/adi,ltc2688.yaml
> b/Documentation/devicetree/bindings/iio/dac/adi,ltc2688.yaml
> > new file mode 100644
> > index 000000000000..ecd0943fb813
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iio/dac/adi,ltc2688.yaml
> > @@ -0,0 +1,147 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id:
> https://urldefense.com/v3/__http://devicetree.org/schemas/iio/dac/
> adi,ltc2688.yaml*__;Iw!!A3Ni8CS0y2Y!qhcjFFDY939hv3Lo2iT1fAIbSObt
> YscKoXjAnLgWZRNG6_WE2WXgZ8AdE4FUwg$
> > +$schema:
> https://urldefense.com/v3/__http://devicetree.org/meta-
> schemas/core.yaml*__;Iw!!A3Ni8CS0y2Y!qhcjFFDY939hv3Lo2iT1fAIbS
> ObtYscKoXjAnLgWZRNG6_WE2WXgZ8BOzIvN9g$
> > +
> > +title: Analog Devices LTC2688 DAC
> > +
> > +maintainers:
> > +  - Nuno Sá <nuno.sa@xxxxxxxxxx>
> > +
> > +description: |
> > +  Analog Devices LTC2688 16 channel, 16 bit, +-15V DAC
> > +  https://www.analog.com/media/en/technical-
> documentation/data-sheets/ltc2688.pdf
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - adi,ltc2688
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  vcc-supply:
> > +    description: Analog Supply Voltage Input.
> > +
> > +  iovcc-supply:
> > +    description: Digital Input/Output Supply Voltage.
> > +
> > +  vref-supply:
> > +    description:
> > +      Reference Input/Output. The voltage at the REF pin sets the full-
> scale
> > +      range of all channels. By default, the internal reference is routed
> to
> > +      this pin.
> 
> Perhaps "If not provided the internal reference is used and also
> provided on the
> VREF pin".

Sure...

> > +
> > +  clr-gpios:
> > +    description:
> > +      If specified, it will be asserted during driver probe. As the line is
> > +      active low, it should be marked GPIO_ACTIVE_LOW.
> > +    maxItems: 1
> > +
> > +  '#address-cells':
> > +    const: 1
> > +
> > +  '#size-cells':
> > +    const: 0
> > +
> > +patternProperties:
> > +  "^channel@([0-9]|1[0-5])$":
> > +    type: object
> > +
> > +    properties:
> > +      reg:
> > +        description: The channel number representing the DAC output
> channel.
> > +        maximum: 15
> > +
> > +      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. It will result in a different ABI for the
> > +          channel.
> 
> The ABI bit is a linux specific part so shouldn't be in the binding.  Just
> leave
> it unsaid.

Makes sense...
> > +        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: -15000000
> > +              - const: 15000000
> 
> Not necessarily a thing to do now, but this is common enough we
> should
> make it a standard DAC channel property.
> 
> > +
> > +      adi,overrange:
> > +        description: Enable 5% overrange over the selected full scale
> range.
> > +        type: boolean
> > +
> > +      clocks:
> > +        maxItems: 1
> > +
> > +      adi,toggle-dither-input:
> > +        description:
> > +          Selects the TGPx pin to be associated with this channel. This
> setting
> > +          only makes sense for toggle or dither enabled channels. If
> > +          @adi,toggle-mode is not set and this property is given, the
> channel is
> > +          assumed to be a dither capable channel. Note that multiple
> channels
> > +          can be mapped to the same pin. If this setting is given, the
> > +          respective @clock must also be provided. Mappings between
> this and
> > +          clocks
> 
> That's not clear, mapping between this an input pin is probably more
> accurate?

Yeah, you're right. When I added this, I had the clock-names properties with 
these exact names. So, in the first version it was more acceptable but since
I removed clock-names, this is not clear anymore...

> > +            0 - TGP1
> > +            1 - TGP2
> > +            2 - TGP3
> > +        $ref: /schemas/types.yaml#/definitions/uint32
> > +        enum: [0, 1, 2]
> > +
> > +    dependencies:
> > +      adi,toggle-dither-input: [ clocks ]
> > +
> > +    required:
> > +      - reg
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +
> > +    spi {
> > +          #address-cells = <1>;
> > +          #size-cells = <0>;
> > +          ltc2688: ltc2688@0 {
> > +                  compatible = "adi,ltc2688";
> > +                  reg = <0>;
> > +
> > +                  vcc-supply = <&vcc>;
> > +                  iovcc-supply = <&vcc>;
> > +                  vref-supply = <&vref>;
> > +
> > +                  #address-cells = <1>;
> > +                  #size-cells = <0>;
> > +                  channel@0 {
> > +                          reg = <0>;
> > +                          adi,toggle-mode;
> 
> Can do this without adi,toggle-dither-input?

Yes, In this case it will assume SW toggle and expose the _symbol
interface...

- Nuno Sá




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