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

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Date:   Tue, 26 Apr 2022 16:26:54 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        <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 Mon, 2022-04-25 at 12:52 +0200, Krzysztof Kozlowski wrote:
> 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://urldefense.com/v3/__https://elixir.bootlin.com/linux/latest/source/drivers/regulator/core.c*L3815__;Iw!!CTRNKA9wMg0ARbw!35L9ISPWDpbGPsLEc0935D2nWTLtaLSNfPipvteddPaxwO2i_KaN0wfWegpkyaPjjagW$
> >  
> 
> 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

Hello Krzysztof,

Thanks for your review!
I will send next version to modify the description of mediatek,cci when
the driver part is explained clear.

BRs,
Rex