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Message-ID: <9da01fb1-9bab-436b-af49-783e44821b26@nokia.com>
Date: Thu, 1 Feb 2024 16:03:59 +0100
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH RESEND] arm: topology: Fix missing clock-frequency
 property warning
Content-Language: en-US
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
 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>
From: Stefan Wiehler <stefan.wiehler@nokia.com>
Organization: Nokia
In-Reply-To: <dfccb849-67b6-489b-8e83-3df1f9b29877@linaro.org>
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> 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.

Kind regards,

Stefan

[1] 
https://devicetree-specification.readthedocs.io/en/latest/chapter3-devicenodes.html#cpus-node-properties
[2] 
https://devicetree-specification.readthedocs.io/en/latest/chapter3-devicenodes.html#cpus-cpu-node-properties
[3] 
https://devicetree-specification.readthedocs.io/en/latest/chapter3-devicenodes.html#general-properties-of-cpus-cpu-nodes