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

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Date:   Tue, 30 Aug 2022 13:08:40 +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 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.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? 
> 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://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml#L38

Best regards,
Krzysztof