linux-kernel - Re: [PATCH v2 2/7] dt-bindings: phy: mediatek,tphy: add property to set pre-emphasis

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Date:   Wed, 31 Aug 2022 11:14:19 +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>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski@...onical.com>,
        Eddie Hung <eddie.hung@...iatek.com>
Subject: Re: [PATCH v2 2/7] dt-bindings: phy: mediatek,tphy: add property to
 set pre-emphasis

On Tue, 2022-08-30 at 20:38 +0300, Krzysztof Kozlowski wrote:
> On 29/08/2022 11:08, Chunfeng Yun wrote:
> > Add a property to set usb2 phy's pre-emphasis, which used to widen
> > eye
> > opening and boost eye swing.
> > 
> > Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>
> > ---
> > v2: Add more description suggested by Krzysztof
> > ---
> >  .../devicetree/bindings/phy/mediatek,tphy.yaml         | 10
> > ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git
> > a/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> > b/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> > index 848edfb1f677..e0754fb44451 100644
> > --- a/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> > +++ b/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
> > @@ -219,6 +219,16 @@ patternProperties:
> >          minimum: 1
> >          maximum: 15
> >  
> > +      mediatek,pre-emphasis:
> > +        description:
> > +          The level of pre-emphasis which used to widen the eye
> > opening and
> > +          boost eye swing, the unit step is about 4.16% increment;
> > e.g. the
> > +          level 1 means amplitude increases about 4.16%, the level
> > 2 is about
> > +          8.3% etc. (U2 phy)
> > +        $ref: /schemas/types.yaml#/definitions/uint32
> 
> As I proposed - use instead common units. 
As explained before, no units for these value.

> Since only three values are
> allowed - make it an enum. 
Ok,

> These bindings are expected to be
> usable/applicable on several devices, so units, not register values
> which can change between devices, are the proper and reliable way to
> describe a feature.
I prefer to use exact level values, but not the inexact values with
units (e.g. -percent, -microvolt).

Thanks a lot

> 
> 
> Best regards,
> Krzysztof