Re: [PATCH 1/6] dt-bindings: clocks: add binding for generic clock-generators

Alexander Stein
2024-07-10T07:02:45Z

Hello Heiko,

Am Dienstag, 9. Juli 2024, 14:31:16 CEST schrieb Heiko Stuebner:
> In contrast to fixed clocks that are described as ungateable, boards
> sometimes use additional clock generators for things like PCIe reference
> clocks, that need actual supplies to get enabled and enable-gpios to be
> toggled for them to work.

Fixed clocks are intended to be ungateable? Where does this come from?

> This adds a binding for such clock generators that are not configurable
> themself, but need to handle supplies for them to work.
>
> While in a lot of cases the type of the IC used is described in board
> schematics, in some cases just a generic type description like
> "100MHz, 3.3V" might also be used. The binding therefore allows both
> cases. Specifying the type is of course preferred.
>
> The clock-frequency is set in devicetree, because while some clock
> generators have pins to decide between multipls output rates, those
> are generally set statically on the board-layout-level.
>
> Signed-off-by: Heiko Stuebner <heiko@sntech.de>
> ---
> .../bindings/clock/clock-generator.yaml | 62 +++++++++++++++++++
> 1 file changed, 62 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/clock/clock-generator.yaml
>
> diff --git a/Documentation/devicetree/bindings/clock/clock-generator.yaml b/Documentation/devicetree/bindings/clock/clock-generator.yaml
> new file mode 100644
> index 0000000000000..f44e61e414e89
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/clock-generator.yaml
> @@ -0,0 +1,62 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/clock/clock-generator.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Simple clock generators
> +
> +maintainers:
> + - Heiko Stuebner <heiko@sntech.de>
> +
> +properties:
> + $nodename:
> + anyOf:
> + - description:
> + Preferred name is 'clock-<freq>' with <freq> being the output
> + frequency as defined in the 'clock-frequency' property.
> + pattern: "^clock-([0-9]+|[a-z0-9-]+)$"
> + - description: Any name allowed
> + deprecated: true
> +
> + compatible:
> + oneOf:
> + - const: clock-generator
> + - items:
> + - enum:
> + - diodes,pi6c557-03b
> + - diodes,pi6c557-05b
> + - const: clock-generator
> +
> + "#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 clock generator.
> + maxItems: 1
> +
> + vdd-supply:
> + description: handle of the regulator that provides the supply voltage

So essentially only enable-gpios and vdd-supply is added in comparison to
fixed-clock. Does it make sense to add that to the fixed-clocks instead?
Similar to fixed-regulator.

> +
> +required:
> + - compatible
> + - "#clock-cells"
> + - clock-frequency

With this list it's essentially the same as fixed-clock.

Best regards,
Alexander

> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + clock {
> + compatible = "clock-generator";
> + #clock-cells = <0>;
> + clock-frequency = <1000000000>;
> + };
> +...
>

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