linux-kernel - Re: [PATCH v2 1/2] dt-bindings: devfreq: mediatek: Add mtk cci devfreq dt-bindings

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Message-ID: <fe7d2b878c18a42ff36ebd9911ecb562fe29c953.camel@mediatek.com>
Date:   Mon, 11 Apr 2022 20:10:42 +0800
From:   Johnson Wang <johnson.wang@...iatek.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        <cw00.choi@...sung.com>, <krzk+dt@...nel.org>,
        <robh+dt@...nel.org>, <kyungmin.park@...sung.com>
CC:     <khilman@...nel.org>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <jia-wei.chang@...iatek.com>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH v2 1/2] dt-bindings: devfreq: mediatek: Add mtk cci
 devfreq dt-bindings

Hi Krzysztof,
On Fri, 2022-04-08 at 10:17 +0200, Krzysztof Kozlowski wrote:
> On 08/04/2022 07:21, Johnson Wang wrote:
> > Add devicetree binding of mtk cci devfreq on MediaTek SoC.
> > 
> 
> Thank you for your patch. There is something to discuss/improve.
> 
> > Signed-off-by: Johnson Wang <johnson.wang@...iatek.com>
> > Signed-off-by: Jia-Wei Chang <jia-wei.chang@...iatek.com>
> > ---
> >  .../devicetree/bindings/devfreq/mtk-cci.yaml  | 72
> > +++++++++++++++++++
> >  1 file changed, 72 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/devfreq/mtk-
> > cci.yaml
> 
> Filename with vendor prefix, so something like:
> 
> mediatek,cci.yaml

Thank you for your review.
I will take your advice in the next version.
> 
> Also please put it in the "interconnect" directory.
> 

I don't really know about "interconnect".
However, it looks like a Linux framework about data transfer and "NoC".

While this cci driver is more like a power managment which is
responsible for adjusting voltages and frequencies.
In my opinion, "devfreq" should be more suitable.

Please correct me if my understanding is wrong.

> > diff --git a/Documentation/devicetree/bindings/devfreq/mtk-cci.yaml 
> > b/Documentation/devicetree/bindings/devfreq/mtk-cci.yaml
> > new file mode 100644
> > index 000000000000..ef4ea951025c
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/devfreq/mtk-cci.yaml
> > @@ -0,0 +1,72 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: 
> > https://urldefense.com/v3/__http://devicetree.org/schemas/devfreq/mtk-cci.yaml*__;Iw!!CTRNKA9wMg0ARbw!yd_wfLu2nSv0GsJZOGP1S8McsGD9A2SC4Qe0Xg1wEb_yEMVcqHRqdvs-M8YKOGckaagO$
> >  
> > +$schema: 
> > https://urldefense.com/v3/__http://devicetree.org/meta-schemas/core.yaml*__;Iw!!CTRNKA9wMg0ARbw!yd_wfLu2nSv0GsJZOGP1S8McsGD9A2SC4Qe0Xg1wEb_yEMVcqHRqdvs-M8YKOERouJvA$
> >  
> > +
> > +title: MediaTek Cache Coherent Interconnect (CCI) frequency and
> > voltage scaling
> > +
> > +maintainers:
> > +  - Jia-Wei Chang <jia-wei.chang@...iatek.com>
> > +
> > +description: |
> > +  MediaTek Cache Coherent Interconnect (CCI) uses the software
> > devfreq module
> 
> Do not reference software implementation (devfreq).

I will modify it in the next version.

> 
> > +  to scale the clock frequency and adjust the voltage. MediaTek
> > CCI shares
> > +  the same power supplies with CPU, so the scheduling involves
> > with CPUfreq.
> 
> The same - cpufreq.
> 
> Instead, focus on the hardware, what do you describe here?

I will focus on hardware description in the next version.

> 
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - mediatek,mt8183-cci
> > +      - mediatek,mt8186-cci
> > +
> > +  clocks:
> > +    items:
> > +      - description:
> > +          The multiplexer for clock input of CPU cluster.
> > +      - description:
> > +          A parent of "cpu" clock which is used as an intermediate
> > clock source
> > +          when the original CPU is under transition and not stable
> > yet.
> > +
> > +  clock-names:
> > +    items:
> > +      - const: cci
> > +      - const: intermediate
> > +
> > +  operating-points-v2:
> > +    description:
> > +      For details, please refer to
> > +      Documentation/devicetree/bindings/opp/opp-v2.yaml
> 
> No need for description. Just "operating-points-v2: true".
> 
> "opp-table:true" could stay. My previous comment about its removal
> was a
> wrong advice, because opp-table is used for a table being a children
> of
> this device node.
> 
> Best regards,
> Krzysztof


I will remove it and add "opp-table:true"(also example) in the next
version.

Thanks.

BRs,
Johnson Wang