linux-kernel - Re: [PATCH V4 01/14] dt-bindings: cpufreq: mediatek: Add MediaTek CCI property

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Date:   Mon, 25 Apr 2022 12:52:55 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Rex-BC Chen <rex-bc.chen@...iatek.com>, rafael@...nel.org,
        viresh.kumar@...aro.org, robh+dt@...nel.org, krzk+dt@...nel.org,
        matthias.bgg@...il.com
Cc:     jia-wei.chang@...iatek.com, roger.lu@...iatek.com,
        hsinyi@...gle.com, khilman@...libre.com,
        angelogioacchino.delregno@...labora.com, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH V4 01/14] dt-bindings: cpufreq: mediatek: Add MediaTek CCI
 property

On 25/04/2022 12:20, Rex-BC Chen wrote:
>> However I am not sure if you solved your problem... see below:
>>
>>> For example:
>>> mediatek cci set 1.2V originally. When cpufreq want to adjust lower
>>> frequency adn set voltage to 1.0V.
>>> The framework will remain using 1.2V to prevent crash of mediatek
>>> cci.
>>
>> No, regulator_set_voltage() for proc_reg says:
>> "NOTE: If the regulator is shared between several devices then the
>> lowest
>>  request voltage that meets the system constraints will be used."
>>
>> Not the highest. So when your devfreq and cpufreq boots, calling
>> regulator_set_voltage will still cause high frequency and low
>> voltage.
>>
> 
> From the driver comment, I think it still needs to match "meets the
> system constraints".
> 
> From drivers, we can trace the driver and it finally to
> regulator_get_optimal_voltage().
> In [1], the framework will get max voltage while finding each device's
> voltage.
> 
> [1]: 
> https://elixir.bootlin.com/linux/latest/source/drivers/regulator/core.c#L3815

Right, actually in your case it's the regulator_check_consumers() above
that line, because you

I think it's quite generic problem, so would be worth solving for more
regulator consumers, but your approach is fine. At least I do not have
anything smarter, at the moment.

Best regards,
Krzysztof