linux-kernel - Re: [PATCH v2 1/2] dt-bindings: net: dp83826: support TX data voltage tuning

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Message-ID: <cb7b7f91-5fcc-4efe-9066-2eb3de836361@linaro.org>
Date: Thu, 8 Feb 2024 10:12:28 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: POPESCU Catalin <catalin.popescu@...ca-geosystems.com>,
 "davem@...emloft.net" <davem@...emloft.net>,
 "kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com"
 <pabeni@...hat.com>, "robh+dt@...nel.org" <robh+dt@...nel.org>,
 "krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>,
 "conor+dt@...nel.org" <conor+dt@...nel.org>, "afd@...com" <afd@...com>,
 "andrew@...n.ch" <andrew@...n.ch>,
 "hkallweit1@...il.com" <hkallweit1@...il.com>,
 "linux@...linux.org.uk" <linux@...linux.org.uk>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 GEO-CHHER-bsp-development <bsp-development.geo@...ca-geosystems.com>,
 "m.felsch@...gutronix.de" <m.felsch@...gutronix.de>
Subject: Re: [PATCH v2 1/2] dt-bindings: net: dp83826: support TX data voltage
 tuning

On 08/02/2024 10:08, POPESCU Catalin wrote:
> On 08.02.24 09:50, Krzysztof Kozlowski wrote:
>> This email is not from Hexagon’s Office 365 instance. Please be careful while clicking links, opening attachments, or replying to this email.
>>
>>
>> On 08/02/2024 09:48, POPESCU Catalin wrote:
>>> On 08.02.24 08:35, Krzysztof Kozlowski wrote:
>>>> [You don't often get email from krzysztof.kozlowski@...aro.org. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>>>
>>>> This email is not from Hexagon’s Office 365 instance. Please be careful while clicking links, opening attachments, or replying to this email.
>>>>
>>>>
>>>> On 07/02/2024 18:58, Catalin Popescu wrote:
>>>>> Add properties ti,cfg-dac-minus-one-milli-percent and
>>>>> ti,cfg-dac-plus-one-milli-percent to support voltage tuning
>>>>> of logical levels -1/+1 of the MLT-3 encoded TX data.
>>>>>
>>>>> Signed-off-by: Catalin Popescu <catalin.popescu@...ca-geosystems.com>
>>>>> ---
>>>>> Changes in v2:
>>>>>    - squash the 2 DT bindings patches in one single patch
>>>>>    - drop redundant "binding" from the DT bindings patch title
>>>>>    - rename DT properties and define them as percentage
>>>>>    - add default value for each new DT property
>>>>> ---
>>>>>    .../devicetree/bindings/net/ti,dp83822.yaml    | 18 ++++++++++++++++++
>>>>>    1 file changed, 18 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/net/ti,dp83822.yaml b/Documentation/devicetree/bindings/net/ti,dp83822.yaml
>>>>> index db74474207ed..6bbd465e51d6 100644
>>>>> --- a/Documentation/devicetree/bindings/net/ti,dp83822.yaml
>>>>> +++ b/Documentation/devicetree/bindings/net/ti,dp83822.yaml
>>>>> @@ -62,6 +62,24 @@ properties:
>>>>>           for the PHY.  The internal delay for the PHY is fixed to 3.5ns relative
>>>>>           to transmit data.
>>>>>
>>>>> +  ti,cfg-dac-minus-one-milli-percent:
>>>>> +    description: |
>>>>> +       DP83826 PHY only.
>>>>> +       Sets the voltage ratio (with respect to the nominal value)
>>>>> +       of the logical level -1 for the MLT-3 encoded TX data.
>>>>> +    enum: [50000, 56250, 62500, 68750, 75000, 81250, 87500, 93750, 100000,
>>>>> +           106250, 112500, 118750, 125000, 131250, 137500, 143750, 150000]
>>>> I see all values being multiple of basis points, so why not using -bp
>>>> suffix?
>>> I can read :
>>>
>>>     "-bp$":
>>>       $ref: types.yaml#/definitions/int32-array
>>>       description: basis points (1/100 of a percent)
>>>
>>> In my case it's 1/1000 of a percent. As I'm not sure exactly what the
>>> author meant by "basis points", would this apply to my patch as well?
>> So please show me the value which does not fit in -bp.
> 
> "Basis points" doesn't mean anything to me, that's why I was asking for 
> confirmation :)
> I don't have any issue to use "-bp" at all, I'm not pusing against.

https://en.wikipedia.org/wiki/Basis_point

Looks like all your values fit there, at least for these devices. Maybe
you would need to be sure other devices do not require mpercent after all.

Best regards,
Krzysztof