Re: [PATCH 2/4] ASoC: dt-bindings: Add support for the GPIOs driven amplifier

[Rob Herring <robh@kernel.org>]

On Mon, Mar 30, 2026 at 12:16:06PM +0200, Herve Codina wrote:
> Some amplifiers based on analog switches and op-amps can be present in
> the audio path and can be driven by GPIOs in order to control their gain
> value, their mute and/or bypass functions.
> 
> Those components needs to be viewed as audio components in order to be
> fully integrated in the audio path.
> 
> audio-gpio-amplifier allows to consider these GPIO driven amplifiers as
> auxiliary audio devices.
> 
> Signed-off-by: Herve Codina <herve.codina@bootlin.com>
> ---
>  .../bindings/sound/audio-gpio-amp.yaml        | 309 ++++++++++++++++++
>  1 file changed, 309 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/sound/audio-gpio-amp.yaml
> 
> diff --git a/Documentation/devicetree/bindings/sound/audio-gpio-amp.yaml b/Documentation/devicetree/bindings/sound/audio-gpio-amp.yaml
> new file mode 100644
> index 000000000000..15dc898f8574
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/sound/audio-gpio-amp.yaml
> @@ -0,0 +1,309 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/sound/audio-gpio-amp.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Audio amplifier driven by GPIOs
> +
> +maintainers:
> +  - Herve Codina <herve.codina@bootlin.com>
> +
> +description: |
> +  Audio GPIO amplifiers are driven by GPIO in order to control the gain value
> +  of the amplifier, its mute function and/or its bypass function.
> +
> +  Those amplifiers are based on discrete components (analog switches, op-amps
> +  and more) where some of them, mostly analog switches, are controlled by GPIOs
> +  to adjust the gain value of the whole amplifier and/or to control
> +  the mute and/or bypass function.
> +
> +  For instance, the following piece of hardware is a GPIO amplifier
> +
> +                                         +5VA
> +                                           ^
> +                                        |\ |
> +                                        | \
> +        Vin >---------------------------|+ \
> +                                        |   +-------+-----> Vout
> +                .--\/\/\/--+------------|- /        |
> +                |          |            | /         |
> +                v          |            |/ |        |
> +               GND         o               v        |
> +                            \             GND       |
> +       gpio >----------->    \                      |
> +                         o    o                     |
> +                         |    |                     |
> +                         |    '--\/\/\/--.          |
> +                         |               +--\/\/\/--'
> +                         '---------------'
> +
> +  A GPIO driven amplifier can work in several mode depending on the electronic
> +  design.
> +    - points defined:
> +        The values of GPIOs used to control gain set a specific gain value
> +        without any specific relationship between each value. For instance,
> +        using 2 GPIOS:
> +          0b00 <-> -10.0 dB
> +          0b01 <-> +3.0 dB
> +          0b10 <-> 0 dB
> +          0b11 <-> +6.0 dB
> +
> +        This can be described using the gain-points property.
> +
> +    - range defined:
> +        The values of GPIOs used to control gain set a specific gain value
> +        following a linear dB range from a minimum dB value to a maximum dB
> +        value. For instance, using 2 GPIOS:
> +          0b00 <-> -3.0 dB
> +          0b01 <-> 0 db
> +          0b10 <-> +3.0 dB
> +          0b11 <-> +6.0 dB
> +
> +        This can be described using the gain-range property.
> +
> +    - labels defined:
> +        Some electronic design are not meant to a specific dB gain value. In
> +        that case it is relevant to use labels to describe them. For instance,
> +        using 2 GPIOS:
> +          0b00 <-> Low boost
> +          0b01 <-> Middle boost
> +          0b10 <-> High boost
> +          0b11 <-> Max boost
> +
> +        This can be described using the gain-labels property
> +
> +properties:
> +  compatible:
> +    const: audio-gpio-amp

To be consistent with other GPIO controlled devices: gpio-audio-amp

> +
> +  vdd-supply:
> +    description: Main power supply of the amplifier
> +
> +  vddio-supply:
> +    description: Power supply related to the control path
> +
> +  vdda1-supply:
> +    description: Analog power supply
> +
> +  vdda2-supply:
> +    description: Additional analog power supply
> +
> +  mute-gpios:
> +    description: GPIO to control the mute function
> +    maxItems: 1
> +
> +  bypass-gpios:
> +    description: GPIO to control the bypass function
> +    maxItems: 1
> +
> +  gain-gpios:
> +    description: |
> +      GPIOs to control the amplifier gain
> +
> +      The gain value is computed from GPIOs value from 0 to 2^N-1 with N the
> +      number of GPIO described. The first GPIO described is the lsb of the gain
> +      value.
> +
> +      For instance assuming 2 gpios
> +         gain-gpios = <&gpio1 GPIO_ACTIVE_HIGH> <&gpio2 GPIO_ACTIVE_HIGH>;
> +      The gain value will be the following:
> +
> +          gpio1 | gpio2 | gain
> +          ------+-------+-----
> +            0   |    0  | 0b00 -> 0
> +            1   |    0  | 0b01 -> 1
> +            0   |    1  | 0b10 -> 2
> +            1   |    1  | 0b11 -> 3
> +          ------+-------+-----
> +
> +      Note: The gain value, bits set to 1 or 0, indicate the state active (bit
> +            set) or the state inactive (bit unset) of the related GPIO. The
> +            physical voltage corresponding to this active/inactive state is
> +            given by the GPIO_ACTIVE_HIGH and GPIO_ACTIVE_LOW flags.
> +
> +    minItems: 1
> +    maxItems: 32

2^32 levels? Seems like a bit much. Also, unless you can change the 
values of all the GPIOs atomically, aren't you going to get some 
artifacts while the gain is being changed? Unless you mute I guess.

> +
> +  gain-points:
> +    $ref: /schemas/types.yaml#/definitions/int32-matrix
> +    items:
> +      items:
> +        - description: The GPIOs value

Can't this just be the index?

If not, then gain-range could be expressed using gain-points instead.

> +        - description: The related amplifier gain in 0.01 dB unit
> +    minItems: 2
> +    description: |
> +      List of the GPIOs value / Gain value in dB pair defining the gain
> +      set on each GPIOs value.
> +
> +      With 2 GPIOs controlling the gain, GPIOs value can be 0, 1, 2 and 3.
> +      Assuming that GPIOs values set the hardware gains according to the
> +      following table:
> +
> +         GPIOs | Hardware
> +         value | amplification
> +         ------+--------------
> +           0   | -10.0 dB
> +           1   | +3.0 dB
> +           2   | 0 dB
> +           3   | +6.0 dB
> +         ------+--------------
> +
> +      The description using gain points can be:
> +        gain-points = <0 (-1000)>, <1 300>, <2 0>, <3 600>;
> +
> +  gain-range:
> +    $ref: /schemas/types.yaml#/definitions/int32-array
> +    items:
> +      - description: Gain in 0.01 dB unit when all GPIOs are inactive
> +      - description: Gain in 0.01 dB unit when all GPIOs are active
> +    description: |
> +      Gains (in 0.01 dB unit) set by the extremum (minimal and maximum) value
> +      of GPIOs. The following formula must be satisfied.
> +
> +               gain-range[1] - gain-range[0]
> +      Gain  = ------------------------------- x GPIO_value + gain-range[0]
> +                        2^N - 1
> +
> +      With N, the number of GPIOs used to control the gain and Gain computed in
> +      0.01 dB unit.
> +
> +      With 2 GPIOs controlling the gain, GPIOs value can be 0, 1, 2 and 3.
> +      Assuming that gain value set the hardware according to the following
> +      table:
> +
> +         GPIOs | Hardware 1    | Hardware 2
> +         value | amplification | amplification
> +         ------+---------------+---------------
> +           0   | -3.0 dB       |  +10.0 dB
> +           1   | 0 dB          |  +5.0 dB
> +           2   | +3.0 dB       |  0 dB
> +           3   | +6.0 dB       |  -5.0 dB
> +         ------+---------------+---------------
> +
> +      The description for hardware 1 using a gain range can be:
> +        gain-range = <(-300) 600>;
> +
> +      The description for hardware 2 using a gain range can be:
> +        gain-range = <1000 (-500)>;
> +
> +  gain-labels:
> +    $ref: /schemas/types.yaml#/definitions/string-array

minItems: 2
maxItems: 0x100000000

> +    description: |
> +      List of the gain labels attached to the combination of GPIOs controlling
> +      the gain. The first label is related to the gain value 0, the second label
> +      is related to the gain value 1 and so on.
> +
> +      With 2 GPIOs controlling the gain, GPIOs value can be 0, 1, 2 and 3.
> +      Assuming that gain value set the hardware according to the following
> +      table:
> +
> +         GPIOs | Hardware
> +         value | amplification
> +         ------+--------------
> +           0   | Low
> +           1   | Middle
> +           2   | High
> +           3   | Max
> +         ------+--------------
> +
> +      The description using gain labels can be:
> +        gain-labels = "Low", "Middle", "High", "Max";

Do we need to allow these to be anything? It's going to get hard to come 
up with 2^32 names. 

> +
> +dependencies:
> +  gain-points: [ gain-gpios ]
> +  gain-range: [ gain-gpios ]
> +  gain-labels: [ gain-gpios ]

gain-gpios is really optional?

> +
> +required:
> +  - compatible
> +  - vdd-supply
> +
> +anyOf:
> +  - required:
> +      - gain-gpios
> +  - required:
> +      - mute-gpios
> +  - required:
> +      - bypass-gpios
> +
> +allOf:
> +  - $ref: dai-common.yaml#
> +  - if:
> +      required:
> +        - gain-points
> +    then:
> +      properties:
> +        gain-range: false
> +        gain-labels: false
> +  - if:
> +      required:
> +        - gain-range
> +    then:
> +      properties:
> +        gain-points: false
> +        gain-labels: false
> +  - if:
> +      required:
> +        - gain-labels
> +    then:
> +      properties:
> +        gain-points: false
> +        gain-range: false
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    /* Gain controlled by gpios */
> +    amplifier0 {

amplifier-0

> +        compatible = "audio-gpio-amp";
> +        vdd-supply = <&regulator>;
> +        gain-gpios = <&gpio 0 GPIO_ACTIVE_HIGH>, <&gpio 1 GPIO_ACTIVE_HIGH>;
> +    };
> +
> +    /* Gain controlled by gpio using range */
> +    amplifier1 {
> +        compatible = "audio-gpio-amp";
> +        vdd-supply = <&regulator>;
> +        gain-gpios = <&gpio 0 GPIO_ACTIVE_HIGH>, <&gpio 1 GPIO_ACTIVE_HIGH>;
> +        gain-range = <(-300) 600>;
> +    };
> +
> +    /* Gain controlled by gpio using points */
> +    amplifier2 {
> +        compatible = "audio-gpio-amp";
> +        vdd-supply = <&regulator>;
> +        gain-gpios = <&gpio 0 GPIO_ACTIVE_HIGH>, <&gpio 1 GPIO_ACTIVE_HIGH>;
> +        gain-points = <0 (-1000)>, <1 300>, <2 0>, <3 600>;
> +    };
> +
> +    /* Gain controlled by gpio with labels */
> +    amplifier3 {
> +        compatible = "audio-gpio-amp";
> +        vdd-supply = <&regulator>;
> +        gain-gpios = <&gpio 0 GPIO_ACTIVE_HIGH>;
> +        gain-labels = "Low", "High";
> +    };
> +
> +    /* A mutable amplifier without any gain control */
> +    amplifier4 {
> +        compatible = "audio-gpio-amp";
> +        vdd-supply = <&regulator>;
> +        mute-gpios = <&gpio 0 GPIO_ACTIVE_HIGH>;

This case is just simple-amplifier...

> +    };
> +
> +    /*  Several supplies, gain controlled using range, mute and bypass */
> +    amplifier5 {
> +        compatible = "audio-gpio-amp";
> +        vdd-supply = <&regulator>;
> +        vddio-supply = <&regulator1>;
> +        vdda1-supply = <&regulator2>;
> +        gain-gpios = <&gpio 0 GPIO_ACTIVE_HIGH>, <&gpio 1 GPIO_ACTIVE_HIGH>;
> +        gain-range = <(-300) 600>;
> +        mute-gpios = <&gpio 2 GPIO_ACTIVE_HIGH>;
> +        bypass-gpios = <&gpio 3 GPIO_ACTIVE_HIGH>;
> +    };
> +...
> -- 
> 2.53.0
>