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

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Message-ID: <000babd8-5980-3d77-f156-324b3442cbe7@linaro.org>
Date:   Fri, 26 Aug 2022 09:36:57 +0300
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        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 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.yaml | 7
>>>>> +++++++
>>>>>  1 file changed, 7 insertions(+)
>>>>>
>>>>> diff --git
>>>>> a/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
>>>>> b/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
>>>>> index 848edfb1f677..aee2f3027371 100644
>>>>> --- a/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
>>>>> +++ b/Documentation/devicetree/bindings/phy/mediatek,tphy.yaml
>>>>> @@ -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? 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...

Best regards,
Krzysztof