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Message-ID: <0a82842d-283c-e266-84f4-6306f29b61da@linaro.org>
Date:   Tue, 30 Aug 2022 13:08:40 +0300
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Subject: Re: [PATCH 2/7] dt-bindings: phy: mediatek,tphy: add property to set
 pre-emphasis
Content-Language: en-US
To:     Chunfeng Yun <chunfeng.yun@mediatek.com>,
        Vinod Koul <vkoul@kernel.org>, Rob Herring <robh+dt@kernel.org>
Cc:     Kishon Vijay Abraham I <kishon@ti.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-phy@lists.infradead.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Eddie Hung <eddie.hung@mediatek.com>
References: <20220819091344.2274-1-chunfeng.yun@mediatek.com>
 <20220819091344.2274-2-chunfeng.yun@mediatek.com>
 <438da392-f419-ad76-7e91-aa4aab36e12c@linaro.org>
 <816ecf6287533137b750c8bde9de5830e4229c56.camel@mediatek.com>
 <bee8abe5-0299-d05e-643c-4810aa33f978@linaro.org>
 <1a16cce9fe164bafc06ae193310be71c6f645d75.camel@mediatek.com>
 <000babd8-5980-3d77-f156-324b3442cbe7@linaro.org>
 <114c357f8d7f049d21ede789a292a8e2d45f4c61.camel@mediatek.com>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <114c357f8d7f049d21ede789a292a8e2d45f4c61.camel@mediatek.com>
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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@mediatek.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