netdev - Re: [PATCH 1/3] dt-bindings: net: dp83826: add ti,cfg-dac-minus binding

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Message-ID: <a8d9e78b-12ac-49df-91ff-09d066e8444a@linaro.org>
Date: Fri, 12 Jan 2024 14:47:29 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: POPESCU Catalin <catalin.popescu@...ca-geosystems.com>,
 "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, "davem@...emloft.net"
 <davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
 "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>,
 "hkallweit1@...il.com" <hkallweit1@...il.com>,
 "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>
Subject: Re: [PATCH 1/3] dt-bindings: net: dp83826: add ti,cfg-dac-minus
 binding

On 12/01/2024 14:41, POPESCU Catalin wrote:
> On 11.01.24 18:21, 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 11/01/2024 17:59, POPESCU Catalin wrote:
>>> On 11.01.24 17:52, Russell King (Oracle) 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 Thu, Jan 11, 2024 at 04:45:26PM +0000, POPESCU Catalin wrote:
>>>>> On 11.01.24 17:35, Andrew Lunn wrote:
>>>>>> [You don't often get email from andrew@...n.ch. 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 Thu, Jan 11, 2024 at 05:19:25PM +0100, Catalin Popescu wrote:
>>>>>>> Add property ti,cfg-dac-minus to allow for voltage tuning
>>>>>>> of logical level -1 of the MLT-3 encoded data.
>>>>>>>
>>>>>>> Signed-off-by: Catalin Popescu <catalin.popescu@...ca-geosystems.com>
>>>>>>> ---
>>>>>>>     Documentation/devicetree/bindings/net/ti,dp83822.yaml | 9 +++++++++
>>>>>>>     1 file changed, 9 insertions(+)
>>>>>>>
>>>>>>> diff --git a/Documentation/devicetree/bindings/net/ti,dp83822.yaml b/Documentation/devicetree/bindings/net/ti,dp83822.yaml
>>>>>>> index db74474207ed..2f010333be49 100644
>>>>>>> --- a/Documentation/devicetree/bindings/net/ti,dp83822.yaml
>>>>>>> +++ b/Documentation/devicetree/bindings/net/ti,dp83822.yaml
>>>>>>> @@ -62,6 +62,15 @@ properties:
>>>>>>>            for the PHY.  The internal delay for the PHY is fixed to 3.5ns relative
>>>>>>>            to transmit data.
>>>>>>>
>>>>>>> +  ti,cfg-dac-minus:
>>>>>>> +    description: |
>>>>>>> +       DP83826 PHY only.
>>>>>>> +       Sets the voltage ratio of the logical level -1 for the MLT-3 encoded data.
>>>>>>> +       0 = 50%, 1 = 56.25%, 2 = 62.50%, 3 = 68.75%, 4 = 75%, 5 = 81.25%, 6 = 87.50%,
>>>>>>> +       7 = 93.75%, 8 = 100%, 9 = 106.25%, 10 = 112.50%, 11 = 118.75%, 12 = 125%,
>>>>>>> +       13 = 131.25%, 14 = 137.50%, 15 = 143.75%, 16 = 150%.
>>>>>>> +    enum: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]
>>>>>> We try to avoid register values in DT. We use real units. This is a
>>>>>> voltage you are configuring, so can you change the unit to millivolts?
>>>>>> Have the driver do the conversion of volts to register value.
>>>>>>
>>>>>> Is it possible to configure any of the other logical levels?
>>>>> Hi Andrew,
>>>>> These are not raw register values and these are not voltage values but
>>>>> voltage ratios. I'm mapping the voltage ratios to enum values [0-16]
>>>>> which are converted to register raw values by the driver. I don't see a
>>>>> better way to do this.
>>>>           enum: [ 5000, 5625, 6250, 6875, 7500, 8125, 8750, 9375, 10000,
>>>>                   10625, 11250, 11875, 12500 13125, 13750, 14375, 15000 ]
>>>>
>>>> ?
>>> I'm okay with that approach if there's no better one. I would need to
>>> remove the register raw values tables from the driver and use a switch
>>> statement to map those values to raw values.
>> You can also use -bp or -percent:
>> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml
> 
>    ti,cfg-dac-minus-percent:
>      description: |
>         DP83826 PHY only.
>         Sets the voltage ratio of the logical level -1 relative to the
> nominal level for the MLT-3 encoded TX data.
>      enum: [50, 56, 62, 68, 75, 81, 87, 93, 100, 106, 112, 118, 125,
> 131, 137, 143, 150]
>      default: 100

Yes, which would also solve your problem of binding errors. But does not
remove the need of testing it before sending to the lists.

Best regards,
Krzysztof