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

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Message-ID: <2e5852b9e94b9a8d0261ce7ad79f4329.sboyd@kernel.org>
Date: Tue, 09 Jul 2024 14:45:20 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Heiko Stuebner <heiko@...ech.de>, mturquette@...libre.com
Cc: robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, heiko@...ech.de, quentin.schulz@...rry.de, linux-clk@...r.kernel.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH 1/6] dt-bindings: clocks: add binding for generic clock-generators

Quoting Heiko Stuebner (2024-07-09 05:31:16)
> 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.
> 
> This adds a binding for such clock generators that are not configurable
> themself, but need to handle supplies for them to work.

Sounds like vdd-supply is required?

> 
> 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@...ech.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@...ech.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

Drop the deprecated stuff from the fixed-clock binding?

> +
> +  compatible:
> +    oneOf:
> +      - const: clock-generator
> +      - items:
> +          - enum:
> +              - diodes,pi6c557-03b

I see this datasheet[1]. Can that link be included somewhere? That shows
there's a clock input pin, which means I expect a 'clocks' property.

Maybe instead of creating a generic binding just make a binding for
these diodes parts? It certainly looks like a generic binding could come
later when another vendor supports the same binding.

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

This is the same required properties as fixed rate clocks. I'd guess
that at least 'enable-gpios' or 'vdd-supply' should also be required, or
the node would simply use fixed-clock compatible.

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

[1] https://diodes.com/assets/Datasheets/PI6C557-03B.pdf