linux-kernel - Re: [PATCH v2 2/4] dt-bindings: arm: mediatek: Add new bindings of MediaTek frequency hopping

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Message-ID: <47ad92dfc593681508fcf09df1303cdfe86c4202.camel@mediatek.com>
Date:   Thu, 15 Sep 2022 12:00:40 +0800
From:   Johnson Wang <johnson.wang@...iatek.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <sboyd@...nel.org>
CC:     <linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        Edward-JW Yang <edward-jw.yang@...iatek.com>
Subject: Re: [PATCH v2 2/4] dt-bindings: arm: mediatek: Add new bindings of
 MediaTek frequency hopping

Hi Angelo,

Thanks for your review.

On Wed, 2022-09-14 at 15:46 +0200, AngeloGioacchino Del Regno wrote:
> Il 14/09/22 14:45, Johnson Wang ha scritto:
> > Add the new binding documentation for MediaTek frequency hopping
> > and spread spectrum clocking control.
> > 
> > Co-developed-by: Edward-JW Yang <edward-jw.yang@...iatek.com>
> > Signed-off-by: Edward-JW Yang <edward-jw.yang@...iatek.com>
> > Signed-off-by: Johnson Wang <johnson.wang@...iatek.com>
> > ---
> >   .../bindings/arm/mediatek/mediatek,fhctl.yaml | 47
> > +++++++++++++++++++
> >   1 file changed, 47 insertions(+)
> >   create mode 100644
> > Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yaml
> > 
> > diff --git
> > a/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yam
> > l
> > b/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yam
> > l
> > new file mode 100644
> > index 000000000000..7b0fd0889bb6
> > --- /dev/null
> > +++
> > b/Documentation/devicetree/bindings/arm/mediatek/mediatek,fhctl.yam
> > l
> > @@ -0,0 +1,47 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: 
> > https://urldefense.com/v3/__http://devicetree.org/schemas/arm/mediatek/mediatek,fhctl.yaml*__;Iw!!CTRNKA9wMg0ARbw!3sumdhtrK5Ah5_rfIilgm4UUmnwkkqMpc3r_ZfkLfsXsLn-_AKm9ZokhJGD1Fl-gJpckAKHZh-jNVW64KRU8Duv1kg$
> >  
> > +$schema: 
> > https://urldefense.com/v3/__http://devicetree.org/meta-schemas/core.yaml*__;Iw!!CTRNKA9wMg0ARbw!3sumdhtrK5Ah5_rfIilgm4UUmnwkkqMpc3r_ZfkLfsXsLn-_AKm9ZokhJGD1Fl-gJpckAKHZh-jNVW64KRWMb8jIsw$
> >  
> > +
> > +title: MediaTek frequency hopping and spread spectrum clocking
> > control
> > +
> > +maintainers:
> > +  - Edward-JW Yang <edward-jw.yang@...iatek.com>
> > +
> > +description: |
> > +  Frequency hopping control (FHCTL) is a piece of hardware that
> > control
> > +  some PLLs to adopt "hopping" mechanism to adjust their
> > frequency.
> > +  Spread spectrum clocking (SSC) is another function provided by
> > this hardware.
> > +
> > +properties:
> > +  compatible:
> > +    const: mediatek,mt8186-fhctl
> > +
> > +  reg:
> > +    maxItems: 1
> 
> There are still a few issues in this binding that I can immediately
> see...
> 
> > +
> > +  clocks:
> 
> MT8195 has 23 PLLs, MT8186 has 14, but perhaps in the future we may
> see
> something more than that on some newer SoC, so...
> 
>    clocks:
>      maxItems: 30

May I add "minItems: 1" to clocks property?

Without this, dt_binding_check will fail because we don't have enough
clocks in the example. (Both MT8195 and MT8186 don't have 30 PLLs)

> 
> > +    description: Phandles of the PLL with FHCTL hardware
> > capability.
> > +
> > +  mediatek,hopping-ssc-percents:
> > +    description: The percentage of spread spectrum clocking for
> > one PLL.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> 
> This is an array, so...
> $ref: /schemas/types.yaml#/definitions/uint32-array
> 
> ...also, maxItems?

As you know, mediatek,hopping-ssc-percents property is used to specify
ssc rate for matching clocks.

If we have to add maxItems, I think we should specify the same value
as clocks property. Is my understanding wrong?


Thanks!

BRs,
Johnson Wang
> 
> and you should also specify:
> 
> default: 0   <- because, by default, SSC is disabled
> minimum: 0   <- because this is the minimum accepted value
> 
> 
> Regards,
> Angelo
> 
> > +    maximum: 8
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - clocks
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/clock/mt8186-clk.h>
> > +    fhctl: fhctl@...0ce00 {
> > +        compatible = "mediatek,mt8186-fhctl";
> > +        reg = <0x1000c000 0xe00>;
> > +        clocks = <&apmixedsys CLK_APMIXED_MSDCPLL>;
> > +        mediatek,hopping-ssc-percents = <3>;
> > +    };
> 
>