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Subject: Re: [TEGRA194_CPUFREQ PATCH v5 1/4] dt-bindings: arm: Add t194 ccplex
 compatible and bpmp property
To:     Rob Herring <robh@kernel.org>
CC:     <rjw@rjwysocki.net>, <viresh.kumar@linaro.org>,
        <catalin.marinas@arm.com>, <will@kernel.org>,
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        <mperttunen@nvidia.com>, Sumit Gupta <sumitg@nvidia.com>
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From:   Sumit Gupta <sumitg@nvidia.com>
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Date:   Tue, 14 Jul 2020 17:13:47 +0530
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> On Mon, Jul 13, 2020 at 07:36:46PM +0530, Sumit Gupta wrote:
>> To do frequency scaling on all CPUs within T194 CPU Complex, we need
>> to query BPMP for data on valid operating points. Document a compatible
>> string under 'cpus' node to represent the CPU Complex for binding drivers
>> like cpufreq which don't have their node or CPU Complex node to bind to.
>> Also, document a property to point to the BPMP device that can be queried
>> for all CPUs.
> 
> The cpus.yaml binding documents what's in 'cpu' nodes, not 'cpus'
> node. AIUI, the latter is what you want. You should do your own schema
> file here.
> 
Do you mean to change existing file name from 'cpus.yaml' to 'cpu.yaml' 
and create new 'cpus.yaml' file?
I think it's better to incorporate the change in existing 'cpus.yaml' 
file to keep both cpu@X and cpus node details together. Please suggest.

>>
>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>> ---
>>   Documentation/devicetree/bindings/arm/cpus.yaml | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/arm/cpus.yaml b/Documentation/devicetree/bindings/arm/cpus.yaml
>> index a018147..9b328e3 100644
>> --- a/Documentation/devicetree/bindings/arm/cpus.yaml
>> +++ b/Documentation/devicetree/bindings/arm/cpus.yaml
>> @@ -162,6 +162,7 @@ properties:
>>         - nvidia,tegra132-denver
>>         - nvidia,tegra186-denver
>>         - nvidia,tegra194-carmel
>> +      - nvidia,tegra194-ccplex
> 
> Tegra194 has 2 different CPUs?
> 
No, T194 SOC has homogeneous architecture with four clusters where each 
cluster has two symmetric cores. 'nvidia,tegra194-carmel' compatible 
string represents each cpu. 'nvidia,tegra194-ccplex' string represents 
the CPU Complex to bind cpufreq driver. The change was done as per 
discussion [1]

>>         - qcom,krait
>>         - qcom,kryo
>>         - qcom,kryo260
>> @@ -255,6 +256,15 @@ properties:
>>
>>         where voltage is in V, frequency is in MHz.
>>
>> +  nvidia,bpmp:
>> +    $ref: '/schemas/types.yaml#/definitions/phandle'
>> +    description: |
>> +      Specifies the bpmp node that needs to be queried to get
>> +      operating point data for all CPUs.
>> +
>> +      Optional for systems that have a "compatible"
>> +      property value of "nvidia,tegra194-ccplex".
>> +
>>     power-domains:
>>       $ref: '/schemas/types.yaml#/definitions/phandle-array'
>>       description:
>> @@ -340,6 +350,7 @@ required:
>>
>>   dependencies:
>>     rockchip,pmu: [enable-method]
>> +  nvidia,bpmp: [compatible]
>>
>>   examples:
>>     - |
>> --
>> 2.7.4
>>

[1] https://marc.info/?l=linux-arm-kernel&m=158999171528418&w=2