Date:   Wed, 18 Aug 2021 15:59:39 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Peter Chen <peter.chen@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-spi@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-mmc@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v8 06/34] dt-bindings: clock: tegra-car: Document new
 tegra-clocks sub-node

On Tue, Aug 17, 2021 at 04:27:26AM +0300, Dmitry Osipenko wrote:
> Document tegra-clocks sub-node which describes Tegra SoC clocks that
> require a higher voltage of the core power domain in order to operate
> properly on a higher clock rates.  Each node contains a phandle to OPP
> table and power domain.
> 
> The root PLLs and system clocks don't have any specific device dedicated
> to them, clock controller is in charge of managing power for them.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  .../bindings/clock/nvidia,tegra20-car.yaml    | 51 +++++++++++++++++++
>  1 file changed, 51 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/clock/nvidia,tegra20-car.yaml b/Documentation/devicetree/bindings/clock/nvidia,tegra20-car.yaml
> index 459d2a525393..7f5cd27e4ce0 100644
> --- a/Documentation/devicetree/bindings/clock/nvidia,tegra20-car.yaml
> +++ b/Documentation/devicetree/bindings/clock/nvidia,tegra20-car.yaml
> @@ -42,6 +42,48 @@ properties:
>    "#reset-cells":
>      const: 1
>  
> +  tegra-clocks:
> +    description: child nodes are the output clocks from the CAR
> +    type: object
> +
> +    patternProperties:
> +      "^[a-z]+[0-9]+$":
> +        type: object
> +        properties:
> +          compatible:
> +            allOf:
> +              - items:
> +                  - enum:
> +                      - nvidia,tegra20-sclk
> +                      - nvidia,tegra30-sclk
> +                      - nvidia,tegra30-pllc
> +                      - nvidia,tegra30-plle
> +                      - nvidia,tegra30-pllm
> +              - const: nvidia,tegra-clock
> +
> +          operating-points-v2:
> +            $ref: /schemas/types.yaml#/definitions/phandle
> +            description:
> +              Phandle to OPP table that contains frequencies, voltages and
> +              opp-supported-hw property, which is a bitfield indicating
> +              SoC process or speedo ID mask.
> +
> +          clocks:
> +            items:
> +              - description: node's clock
> +
> +          power-domains:
> +            maxItems: 1
> +            description: phandle to the core SoC power domain
> +
> +        required:
> +          - compatible
> +          - operating-points-v2
> +          - clocks
> +          - power-domains
> +
> +        additionalProperties: false
> +
>  required:
>    - compatible
>    - reg
> @@ -59,6 +101,15 @@ examples:
>          reg = <0x60006000 0x1000>;
>          #clock-cells = <1>;
>          #reset-cells = <1>;
> +
> +        tegra-clocks {
> +            sclk {
> +                compatible = "nvidia,tegra20-sclk", "nvidia,tegra-clock";
> +                operating-points-v2 = <&opp_table>;
> +                clocks = <&tegra_car TEGRA20_CLK_SCLK>;
> +                power-domains = <&domain>;
> +            };
> +        };

I wonder if it'd be better to match on the name of the node rather than
add an artificial compatible string. We usually use the compatible
string to match a device, but here you're really trying to add
information about a resource provided by the CAR controller.

We do similar things for example in PMIC bindings where the individual
regulators are represented in the device tree via nodes named after the
regulator.

You could then also leave out the clocks property, which is weird as it
is because it's basically a self-reference. But you don't really need
the reference here in the first place because the CAR is already the
parent of SCLK.

Also, I don't think the tegra- prefix is necessary here. The parent node
is already identified as Tegra via the compatible string.

In the case of CAR, I'd imagine something like:

	clocks {
		sclk {
			operating-points-v2 = <&opp_table>;
			power-domains = <&domain>;
		};
	};

Now you've only got the bare minimum in here that you actually add. All
the other data that you used to have is simply derived from the parent.

Thierry

>      };
>  
>      usb-controller@...04000 {
> -- 
> 2.32.0
> 

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