Re: [PATCH 1/4] dt-bindings: sound: Add simple-iio-aux

Herve Codina
2023-04-26T07:36:32Z

Hi Rob,

On Tue, 25 Apr 2023 12:30:29 -0500
Rob Herring <robh@kernel.org> wrote:

> On Fri, Apr 21, 2023 at 02:41:19PM +0200, Herve Codina wrote:
> > Industrial I/O devices can be present in the audio path.
> > These devices needs to be viewed as audio components in order to be
> > fully integrated in the audio path.
> >
> > simple-iio-aux allows to consider these Industrial I/O devices as
> > auxliary audio devices.
>
> What makes it simple? Any binding called simple or generic is a trigger
> for me. Best to avoid those terms. :)

I choose simple-iio-aux because some simple-* already exists.
For instance simple-audio-amplifier or simple-audio-mux.

Do you prefer audio-iio-aux ?
Let me know if I should change.

>
> Examples of devices would be useful here.
>
> >
> > Signed-off-by: Herve Codina <herve.codina@bootlin.com>
> > ---
> > .../bindings/sound/simple-iio-aux.yaml | 65 +++++++++++++++++++
> > 1 file changed, 65 insertions(+)
> > create mode 100644 Documentation/devicetree/bindings/sound/simple-iio-aux.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/sound/simple-iio-aux.yaml b/Documentation/devicetree/bindings/sound/simple-iio-aux.yaml
> > new file mode 100644
> > index 000000000000..fab128fce4fc
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/sound/simple-iio-aux.yaml
> > @@ -0,0 +1,65 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/sound/simple-iio-aux.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Simple IIO auxiliary
> > +
> > +maintainers:
> > + - Herve Codina <herve.codina@bootlin.com>
> > +
> > +description: |
>
> Don't need '|'

Will be fixed.

>
> > + Auxiliary device based on Industrial I/O device channels
> > +
> > +allOf:
> > + - $ref: /schemas/iio/iio-consumer.yaml
>
> You don't need to reference consumer schemas.

Right, will be removed.

>
> > + - $ref: dai-common.yaml#
> > +
> > +properties:
> > + compatible:
> > + const: simple-iio-aux
> > +
> > + io-channels:
> > + description:
> > + Industrial I/O device channels used
> > +
> > + io-channel-names:
> > + description:
> > + Industrial I/O channel names related to io-channels.
> > + These names are used to provides sound controls, widgets and routes names.
> > +
> > + invert:
>
> Property names should globally only have 1 type definition. This is
> generic enough I'd be concerned that's not the case.

What do you mean ?

>
> > + $ref: /schemas/types.yaml#/definitions/uint32-array
> > + description: |
> > + A list of 0/1 flags defining whether or not the related channel is
> > + inverted
> > + items:
> > + enum: [0, 1]
> > + default: 0
> > + description: |
> > + Invert the sound control value compared to the IIO channel raw value.
> > + - 1: The related sound control value is inverted meaning that the
> > + minimum sound control value correspond to the maximum IIO channel
> > + raw value and the maximum sound control value correspond to the
> > + minimum IIO channel raw value.
> > + - 0: The related sound control value is not inverted meaning that the
> > + minimum (resp maximum) sound control value correspond to the
> > + minimum (resp maximum) IIO channel raw value.
> > +
> > +required:
> > + - compatible
> > + - io-channels
> > + - io-channel-names
> > +
> > +unevaluatedProperties: false
> > +
> > +examples:
> > + - |
> > + aux {
> > + compatible = "simple-iio-aux";
> > + io-channels = <&iio 0>, <&iio 1>, <&iio 2>, <&iio 3>;
> > + io-channel-names = "CH0", "CH1", "CH2", "CH3";
>
> Not really useful names. Do you have a real example?

As Mark said, for IIO channel, using CHx makes sense.
See below, I provide a full example.

>
> > + /* Invert CH1 and CH2 */
> > + invert = <0 1 1>;
>
> IMO, invert should be same length as io-channels.

I will update.

Related to this topic, when I wrote this binding, I wanted to add some
rules/constraints in order to:
- Have this property optional
- If present, force to have as many items in the invert array as the
number of items present in the io-channels array.

I never succeed in writing the constraint for the invert property.
It should be possible (it is done for some 'foo' 'foo-names' pair such
as clocks).
Can you tell me if possible in my case and give me some pointers ?

>
> > + };
>
> How do support multiple instances? Say you have 2 sound cards (or 1
> sound card with multiple audio paths) each with different sets of IIO
> channels associated with it. You'd need a link to each 'aux' node. Why
> not just add io-channels to the sound card nodes directly? That's
> already just a virtual, top-level container node grouping all the
> components. I don't see why we need another virtual node grouping a
> subset of them.

I don't see what you mean.
I use a simple-audio-card and here is a full example using several
instances:

spi {
#address-cells = <1>;
#size-cells = <0>;
/* potentiometers present in an input amplifier design */
pot_in: potentiometer@0 {
compatible = "foo,xxx";
reg = <0>;
#io-channel-cells = <1>;
};
/* potentiometers present in an output amplifier design */
pot_out: potentiometer@1 {
compatible = "foo,xxx";
reg = <1>;
#io-channel-cells = <1>;
};
/* A codec */
codec: codec@2 {
compatible = "bar,yyy";
reg = <2>;
sound-name-prefix = "CODEC";
};

};

amp_out: aux-out {
compatible = "simple-iio-aux";
io-channels = <&pot_out 0>, <&pot_out 1>,
io-channel-names = "CH0", "CH1";
invert = <1 1>;
sound-name-prefix = "AMP_OUT";
};

amp_in: aux-in {
compatible = "simple-iio-aux";
io-channels = <&pot_in 0>, <&pot_in 1>;
io-channel-names = "CH0", "CH1";
sound-name-prefix = "AMP_IN";
};

sound {
compatible = "simple-audio-card";
#address-cells = <1>;
#size-cells = <0>;
simple-audio-card,name = "My Sound Card";

simple-audio-card,aux-devs = <&amp_in>, <&amp_out>;
simple-audio-card,routing =
"CODEC IN0", "AMP_IN CH0 OUT",
"CODEC IN1", "AMP_IN CH1 OUT",
"AMP_OUT CH0 IN", "CODEC OUT0",
"AMP_OUT CH1 IN", "CODEC OUT1",

simple-audio-card,dai-link@0 {
...
};
};

Best regards,
Hervé

--
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering