Re: [PATCH v2 1/3] dt-bindings: clocks: add binding for voltage-controlled-oscillators

[Conor Dooley <conor@xxxxxxxxxx>]

On Mon, Jul 15, 2024 at 01:02:49PM +0200, Heiko Stuebner wrote:
> In contrast to fixed clocks that are described as ungateable, boards
> sometimes use additional oscillators for things like PCIe reference
> clocks, that need actual supplies to get enabled and enable-gpios to be
> toggled for them to work.
> 
> This adds a binding for such oscillators that are not configurable
> themself, but need to handle supplies for them to work.
> 
> In schematics they often can be seen as
> 
>          ----------------
> Enable - | 100MHz,3.3V, | - VDD
>          |    3225      |
>    GND - |              | - OUT
>          ----------------
> 
> or similar. The enable pin might be separate but can also just be tied
> to the vdd supply, hence it is optional in the binding.
> 
> Signed-off-by: Heiko Stuebner <heiko@xxxxxxxxx>
> ---
>  .../bindings/clock/voltage-oscillator.yaml    | 49 +++++++++++++++++++
>  1 file changed, 49 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/clock/voltage-oscillator.yaml
> 
> diff --git a/Documentation/devicetree/bindings/clock/voltage-oscillator.yaml b/Documentation/devicetree/bindings/clock/voltage-oscillator.yaml
> new file mode 100644
> index 0000000000000..8bff6b0fd582e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/voltage-oscillator.yaml
> @@ -0,0 +1,49 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/clock/voltage-oscillator.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Voltage controlled oscillator

Voltage controlled oscillator? Really? That sounds far too similar to a
VCO to me, and the input voltage here (according to the description at
least) does not affect the frequency of oscillation.

Why the dedicated binding, rather than adding a supply and enable-gpio
to the existing "fixed-clock" binding? I suspect that a large portion of
"fixed-clock"s actually require a supply that is (effectively)
always-on.

Cheers,
Conor.

> +
> +maintainers:
> +  - Heiko Stuebner <heiko@xxxxxxxxx>
> +
> +properties:
> +  compatible:
> +    const: voltage-oscillator
> +
> +  "#clock-cells":
> +    const: 0
> +
> +  clock-frequency: true
> +
> +  clock-output-names:
> +    maxItems: 1
> +
> +  enable-gpios:
> +    description:
> +      Contains a single GPIO specifier for the GPIO that enables and disables
> +      the oscillator.
> +    maxItems: 1
> +
> +  vdd-supply:
> +    description: handle of the regulator that provides the supply voltage
> +
> +required:
> +  - compatible
> +  - "#clock-cells"
> +  - clock-frequency
> +  - vdd-supply
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    voltage-oscillator {
> +      compatible = "voltage-oscillator";
> +      #clock-cells = <0>;
> +      clock-frequency = <1000000000>;
> +      vdd-supply = <&reg_vdd>;
> +    };
> +...
> -- 
> 2.39.2
>

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