linux-kernel - Re: [PATCH 1/4] dt-bindings: cpufreq: mediatek: transform cpufreq-mediatek into yaml

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Date:   Fri, 1 Apr 2022 21:26:00 +0800
From:   Jia-Wei Chang <jia-wei.chang@...iatek.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
CC:     <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>, <fan.chen@...iatek.com>,
        <louis.yu@...iatek.com>, <roger.lu@...iatek.com>,
        <Allen-yy.Lin@...iatek.com>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        <hsinyi@...gle.com>,
        Jia-Wei Chang <jia-wei.chang@...iatek.corp-partner.google.com>
Subject: Re: [PATCH 1/4] dt-bindings: cpufreq: mediatek: transform
 cpufreq-mediatek into yaml

On Thu, 2022-03-24 at 11:33 +0100, Krzysztof Kozlowski wrote:
> On 24/03/2022 10:38, Jia-Wei Chang wrote:
> > > 
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/cpufreq/cpufreq-
> > > > mediatek.yaml
> > > > b/Documentation/devicetree/bindings/cpufreq/cpufreq-
> > > > mediatek.yaml
> > > > new file mode 100644
> > > > index 000000000000..584946eb3790
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/cpufreq/cpufreq-
> > > > mediatek.yaml
> > > > @@ -0,0 +1,131 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: 
> > > > 
https://urldefense.com/v3/__http://devicetree.org/schemas/cpufreq/cpufreq-mediatek.yaml*__;Iw!!CTRNKA9wMg0ARbw!xbKG4TgD0MRpMLyGJVBZEGpZFrNOclrcxOCx_APKo5Nmg8nF2x5PcBdE0unvL2NdpChkMA$
> > > >  
> > > > +$schema: 
> > > > 
https://urldefense.com/v3/__http://devicetree.org/meta-schemas/core.yaml*__;Iw!!CTRNKA9wMg0ARbw!xbKG4TgD0MRpMLyGJVBZEGpZFrNOclrcxOCx_APKo5Nmg8nF2x5PcBdE0unvL2O8T_oxCQ$
> > > >  
> > > > +
> > > > +title: Mediatek CPUFREQ driver Device Tree Bindings
> > > 
> > > Please remove "driver Device Tree Bindings" because the title
> > > should
> > > describe the hardware. Therefore it could be something like
> > > "Mediatek
> > > SoC CPU frequency and voltage scaling".
> > 
> > Thanks for your suggestion of title.
> > Or should I use the origin title "Binding for MediaTek's CPUFreq
> > driver"?
> 
> Mediatek CPUFREQ
> or
> Mediatek CPU frequency scaling

Ok, I will choose one of it.

> 
> > 
> > > 
> > > How is it related to cpufreq-mediatek-hw.yaml? The names/title
> > > look
> > > unfortunately too similar.
> > 
> > No, mediatek-cpufreq is performing in kernel driver rather than on
> > hardware.
> > On the other hand, mediatek-cpufreq-hw is performing on hardware.
> > That's why "hw" is present in its name.
> 
> Unfortunately, I do not get it. The bindings are only about hardware,
> so
> how bindings could be about CPU frequency scaling not in hardware?

Sorry, let me correct my statements.

For mediatek-cpufreq here, the required hardware are clock and
regulator which have to be under control of mediatek-cpufreq. That's
the reason why it needs bindings.

mediatek-cpufreq scales up and down voltage and frequency via kernel
framework of clock and regulator, however, mediatek-cpufreq-hw delegate
the voltage and frequency control to a hardware agent instead.

> 
> > 
> > > 
> > > In general this does not look like proper bindings (see also
> > > below
> > > lack
> > > of compatible). Bindings describe the hardware, so what is
> > > exactly
> > > the
> > > hardware here?
> > 
> > Except for SoC, there's no requirement of hardware binding for
> > mediatek-cpufreq.
> > mediatek-cpufreq recognizes the compatible of Mediatek SoC while
> > probing.
> 
> What is the hardware here? If there is no requirement for bindings
> for
> mediate-cpufreq, why do we have this patch here?

Sorry, that's my mistake.
Clock and regulator are required hardware for mediatek-cpufreq.

> 
> > 
> > > 
> > > > +
> > > > +maintainers:
> > > > +  - Jia-Wei Chang <jia-wei.chang@...iatek.com>
> > > > +
> > > > +description: |
> > > > +  CPUFREQ is used for scaling clock frequency of CPUs.
> > > > +  The module cooperates with CCI DEVFREQ to manage frequency
> > > > for
> > > > some Mediatek
> > > > +  SoCs.
> > > > +
> > > > +properties:
> > > 
> > > How is this schema going to be applied? I don't see here select
> > > neither
> > > compatible.
> > 
> > As mentioned above, only compatible of SoC is required for
> > mediatek-
> > cpufreq.
> 
> It does not answer my questions. How the schema is going to be
> applied?

Currently, we do use compatible of SoC to probe mediatek-cpufreq.

If the better way is using clock and regulator opp, do you have a
suggestion to approach that?
I mean I can't find a good example from other vendors trying to do that
way. Or maybe I miss something?

> 
> 
> Best regards,
> Krzysztof