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

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Date: Thu, 11 Jan 2024 18:21:29 +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 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

Best regards,
Krzysztof