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Message-ID: <e337bfdb-34dd-428f-b0c5-defd93b24822@linaro.org>
Date: Fri, 2 Feb 2024 11:58:50 +0100
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Subject: Re: [PATCH RESEND] arm: topology: Fix missing clock-frequency
 property warning
Content-Language: en-US
To: Stefan Wiehler <stefan.wiehler@nokia.com>,
 Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
 devicetree@vger.kernel.org
References: <20240201123605.3037829-2-stefan.wiehler@nokia.com>
 <dfccb849-67b6-489b-8e83-3df1f9b29877@linaro.org>
 <9da01fb1-9bab-436b-af49-783e44821b26@nokia.com>
From: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
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In-Reply-To: <9da01fb1-9bab-436b-af49-783e44821b26@nokia.com>
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On 01/02/2024 16:03, Stefan Wiehler wrote:
>> Does this mean the /cpus property is like a default for when a CPU node
>> doesn't specify the clock frequency, or does it mean that the /cpus
>> property should only exist when all the values for each CPU are
>> identical and thus the individual CPU node clock frequency should
>> not be specified.
> 
> Good question, the device tree specification in Section 3.7 [1] says:
> 
>  > The /cpus node may contain properties that are common across cpu
> nodes. See Section 3.8 for details.
> 
> And in Section 3.8 [2]:
> 
>  > Properties that have identical values across cpu nodes may be placed
>  > in the /cpus node instead. A client program must first examine a
>  > specific cpu node, but if an expected property is not found then it
>  > should look at the parent /cpus node. This results in a less verbose
>  > representation of properties which are identical across all CPUs.
> 
> So I think it is pretty clear that it should only be used for 
> common/identical values.
> 
>> Aren't you adding new property? Is it already documented in the
>> bindings? After a quick look I think this is not documented.
> 
> You are right, clock-frequency is not mentioned neither in arm/cpus.yaml 
> nor in any other <arch>/cpus.yaml binding, but the DT spec has it as a 
> required property [3]. Should I add clock-frequency to all 
> <arch>/cpus.yaml bindings? Only the ARM one explicitly mentions 
> following the DT spec.

It should go to dtschema. dtschema cpu.yaml has it, so you need to
propose such to cpus.yaml, probably you could experiment with:
not:
  - required:
      - clock-frequency
  - patternProperties:
      cpu@....
        - required:
            - clock-frequency

Anyway, you cannot just keep adding some OF properties to the code
without documenting them.

Best regards,
Krzysztof