Message-ID: <ec790d2324f1bd53c4a53b58ad29040725d580f5.camel@mediatek.com>
Date:   Fri, 8 Apr 2022 11:14:33 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Jia-Wei Chang <jia-wei.chang@...iatek.com>,
        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 Fri, 2022-04-01 at 18:32 +0200, Krzysztof Kozlowski wrote:
> On 01/04/2022 15:26, Jia-Wei Chang wrote:
> > 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.
> 
> OK, that makes sense, thanks for explanation.
> 
> > 
> > > 
> > > > 
> > > > > 
> > > > > 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.
> 
> Probing and binding to compatible is correct, but there is no
> compatible
> here, so the schema is a no-op. Does nothing.
> 
> > 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?
> 
> One other way (proper) is to use cpufreq-dt and existing bindings. I
> understand that maybe you need some specific bindings here, but I
> fail
> to see how they would work. IOW, you don't have the compatible, no
> select, so nothing can use these bindings. Also bindings do not refer
> to
> any specific hardware, like SoC model.
> 
> It's good that you try to convert existing bindings to DT schema, but
> with that they should be probably fixed/updated to match proper
> bindings.
> 
> Best regards,
> Krzysztof
> 

Hello Krzysztof,

Thanks for your suggestion.
I have discussed with Jia-wei internally.
We want to push next version because we finish to prepare the driver
parts.

For binding part, we want to cancel the transformation to yaml first
and only add the mediatek cci property for cpufreq series in next
version.

I will help Jia-wei to push next version.
If you have any suggestion, we can discuss in the next version (v2) of
this series.

Thanks for your big support!

BRs,
Rex

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