linux-kernel - Re: [TEGRA194_CPUFREQ Patch v3 1/4] dt-bindings: arm: Add t194 ccplex compatible and bpmp property

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Date:   Tue, 23 Jun 2020 11:35:27 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     <rjw@...ysocki.net>, <catalin.marinas@....com>, <will@...nel.org>,
        <thierry.reding@...il.com>, <robh+dt@...nel.org>,
        <devicetree@...r.kernel.org>, <jonathanh@...dia.com>,
        <talho@...dia.com>, <linux-pm@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <bbasu@...dia.com>,
        <mperttunen@...dia.com>, Sumit Gupta <sumitg@...dia.com>
Subject: Re: [TEGRA194_CPUFREQ Patch v3 1/4] dt-bindings: arm: Add t194 ccplex
 compatible and bpmp property



On 22/06/20 12:52 PM, Viresh Kumar wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 22-06-20, 03:04, 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.
> 
> You shouldn't be putting how linux is going to use this information and entries
> shouldn't be made just so cpufreq can bind to a driver.
> 
> Though I see that this is a real hardware register which you can use to interact
> with the firmware ? And so it makes sense to have it, maybe in different form
> though.
> 
CPUFREQ driver doesn't communicate directly with BPMP firmware. It uses 
BPMP node's reference to call api's exported by BPMP driver which 
communicates with BPMP firmware.

> I will let Rob explain what would be the right way of doing this though.
> 
This is already discussed by Thierry with Rob.
Please refer https://marc.info/?l=linux-arm-kernel&m=158999171528418&w=2

>>
>> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
>> ---
>>   Documentation/devicetree/bindings/arm/cpus.yaml | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/arm/cpus.yaml b/Documentation/devicetree/bindings/arm/cpus.yaml
>> index a018147..737b55e 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
>>         - qcom,krait
>>         - qcom,kryo
>>         - qcom,kryo260
>> @@ -255,6 +256,14 @@ properties:
>>
>>         where voltage is in V, frequency is in MHz.
>>
>> +  nvidia,bpmp:
>> +    $ref: '/schemas/types.yaml#/definitions/phandle'
>> +    descrption: |
>> +      Specifies the bpmp node that needs to be queried to get
>> +      operating point data for all CPUs.
>> +
>> +      Optional for NVIDIA Tegra194 Carmel CPUs
>> +
>>     power-domains:
>>       $ref: '/schemas/types.yaml#/definitions/phandle-array'
>>       description:
>> --
>> 2.7.4
> 
> --
> viresh
>