linux-kernel - Re: [PATCH 1/2] dtbindings: clock: Add bindings for Renesas PhiClock

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Message-ID: <6dc67c30-d9c3-5906-a2bc-263ac83df051@linaro.org>
Date:   Thu, 17 Nov 2022 08:39:01 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Alex Helms <alexander.helms.jy@...esas.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org
Cc:     krzysztof.kozlowski+dt@...aro.org, robh+dt@...nel.org,
        sboyd@...nel.org, mturquette@...libre.com, geert+renesas@...der.be
Subject: Re: [PATCH 1/2] dtbindings: clock: Add bindings for Renesas PhiClock

On 16/11/2022 21:11, Alex Helms wrote:
>>> +  clocks:
>>> +    const: 1
>>> +
>>> +  compatible:
>>> +    enum:
>>> +      - renesas,9fgv1006
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  renesas,ss-amount-percent:
>>> +    description: Spread spectrum absolute amount as hundredths of a percent, e.g. 150 is 1.50%.
>>
>> What? If this is percent then it cannot be hundreds of percent. Percent
>> is percent. Use appropriate units.
>> https://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fdevicetree-org%2Fdt-schema%2Fblob%2Fmain%2Fdtschema%2Fschemas%2Fproperty-units.yaml&amp;data=05%7C01%7Calexander.helms.jy%40renesas.com%7C9c13a32848f3434e217108dac7ab69f6%7C53d82571da1947e49cb4625a166a4a2a%7C0%7C0%7C638041836281252737%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=6MULpJhPyyjWSo1SvPCrz6KidE1VEtiiNYk1O5wS1vI%3D&amp;reserved=0
>>
> 
> Values like 0.5% or 2.5% must be representable which is why this
> property is an integer of hundredths of percent. How else would you
> represent a non-integer percent?

With an appropriate unit.

> 
>>> +    minimum: 0
>>> +    maximum: 500
>>> +
>>> +  renesas,ss-modulation-hz:
>>> +    description: Spread spectrum modulation rate in Hz
>>> +    minimum: 30000
>>> +    maximum: 63000
>>> +
>>> +  renesas,ss-direction:
>>> +    $ref: /schemas/types.yaml#/definitions/string
>>> +    description: Spread spectrum direction
>>> +    enum: [ down, center ]
>>> +
>>> +required:
>>> +  - clock-names
>>> +  - '#clock-cells'
>>> +  - compatible
>>> +  - reg
>>> +
>>> +additionalProperties: false
>>> +
>>> +examples:
>>> +  - |
>>> +    ref25: ref25m {
>>> +      compatible = "fixed-clock";
>>> +      #clock-cells = <0>;
>>> +      clock-frequency = <25000000>;
>>> +    };
>>
>> Drop, it's obvious, isn't it?
>>
> 
> I disagree, this may be obvious to someone familiar with how clocks in
> the device tree works but not long ago it was entirely new to me and
> examples like these in the dt schemas were very helpful in getting the
> device up and running. There are several other bindings that define
> external crystals and reference clocks in this way.

It is obvious because it is the same for every device being a consumer
of external clock. There is no point to duplicate non-device related
examples in every device binding.

Best regards,
Krzysztof