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

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Message-ID: <3c180570-ecf9-3db4-c698-39c1b4679c6e@linaro.org>
Date:   Wed, 31 Aug 2022 09:03:45 +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 31/08/2022 06:00, Chunfeng Yun wrote:
> 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.

Then again explain exactly what are the levels. How you wrote it last
time, -bp would do the trick.

Best regards,
Krzysztof