linux-kernel - Re: [PATCH 2/7] dt-bindings: phy: mediatek,tphy: add property to set pre-emphasis

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Date:   Wed, 31 Aug 2022 11:00:57 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Vinod Koul <vkoul@...nel.org>, Rob Herring <robh+dt@...nel.org>
CC:     Kishon Vijay Abraham I <kishon@...com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-phy@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Eddie Hung <eddie.hung@...iatek.com>
Subject: Re: [PATCH 2/7] dt-bindings: phy: mediatek,tphy: add property to
 set pre-emphasis

On Tue, 2022-08-30 at 13:08 +0300, Krzysztof Kozlowski wrote:
> On 29/08/2022 05:37, Chunfeng Yun wrote:
> > On Fri, 2022-08-26 at 09:36 +0300, Krzysztof Kozlowski wrote:
> > > On 26/08/2022 08:36, Chunfeng Yun wrote:
> > > > On Tue, 2022-08-23 at 13:24 +0300, Krzysztof Kozlowski wrote:
> > > > > On 22/08/2022 10:07, Chunfeng Yun wrote:
> > > > > > On Fri, 2022-08-19 at 15:15 +0300, Krzysztof Kozlowski
> > > > > > wrote:
> > > > > > > On 19/08/2022 12:13, Chunfeng Yun wrote:
> > > > > > > > Add a property to set usb2 phy's pre-emphasis.
> > > > > > > > 
> > > > > > > > Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>
> > > > > > > > ---
> > > > > > > >  Documentation/devicetree/bindings/phy/mediatek,tphy.ya
> > > > > > > > ml |
> > > > > > > > 7
> > > > > > > > +++++++
> > > > > > > >  1 file changed, 7 insertions(+)
> > > > > > > > 
> > > > > > > > diff --git
> > > > > > > > a/Documentation/devicetree/bindings/phy/mediatek,tphy.y
> > > > > > > > aml
> > > > > > > > b/Documentation/devicetree/bindings/phy/mediatek,tphy.y
> > > > > > > > aml
> > > > > > > > index 848edfb1f677..aee2f3027371 100644
> > > > > > > > ---
> > > > > > > > a/Documentation/devicetree/bindings/phy/mediatek,tphy.y
> > > > > > > > aml
> > > > > > > > +++
> > > > > > > > b/Documentation/devicetree/bindings/phy/mediatek,tphy.y
> > > > > > > > aml
> > > > > > > > @@ -219,6 +219,13 @@ patternProperties:
> > > > > > > >          minimum: 1
> > > > > > > >          maximum: 15
> > > > > > > >  
> > > > > > > > +      mediatek,pre-emphasis:
> > > > > > > > +        description:
> > > > > > > > +          The selection of pre-emphasis (U2 phy)
> > > > > > > > +        $ref: /schemas/types.yaml#/definitions/uint32
> > > > > > > > +        minimum: 1
> > > > > > > > +        maximum: 3
> > > > > > > 
> > > > > > > Instead of hard-coding register values in bindings, you
> > > > > > > should
> > > > > > > rather
> > > > > > > describe here feature/effect. If it is in units, use unit
> > > > > > > suffixes.
> > > > > > > If
> > > > > > > it is some choice, usually string enum is appropriate.
> > > > > > 
> > > > > > How about changing description as bellow:
> > > > > > 
> > > > > > "The level of pre-emphasis, increases one level, boosts the
> > > > > > relative
> > > > > > amplitudes of signal's higher frequencies components about
> > > > > > 4.16%
> > > > > > (U2
> > > > > > phy)"
> > > > > > 
> > > > > 
> > > > > Still the question is what is the unit. 4.16%?
> > > > 
> > > > No unit, it's a level value, like an index of array.
> > > > 
> > > 
> > > So a value from register/device programming? 
> > 
> > Yes
> > > Rather a regular units
> > > should be used if that's possible. If not, this should be clearly
> > > described here, not some magical number which you encode into
> > > DTS...
> > 
> > Ok, I'll add more descriptions.
> 
> Better use logical value, e.g.
> 
https://urldefense.com/v3/__https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml*L38__;Iw!!CTRNKA9wMg0ARbw!1e-h0R_uwcaHKfKC9qYfaRWYeuWRq1sLCGy3yupNmkFyuW5s1nmRotL7Y0vFG9ETLLTA$
>  
Optional unit may be -percent or -bp, but the value 4.16% * X
(X=1,2,3...)is not an exact value, they are variable in a range and
dependent more factors.
So I think use level value is simple enough.

> 
> Best regards,
> Krzysztof