linux-kernel - Re: [PATCH 1/2] dt-bindings: phy: imx8mq-usb: add phy tuning properties

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Date:   Tue, 18 Apr 2023 11:42:58 +0200
From:   Johannes Zink <j.zink@...gutronix.de>
To:     Rob Herring <robh@...nel.org>
Cc:     kishon@...nel.org, devicetree@...r.kernel.org,
        krzysztof.kozlowski+dt@...aro.org, festevam@...il.com,
        s.hauer@...gutronix.de, vkoul@...nel.org, haibo.chen@....com,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        linux-imx@....com, kernel@...gutronix.de,
        linux-phy@...ts.infradead.org, shawnguo@...nel.org,
        linux-arm-kernel@...ts.infradead.org, jun.li@....com
Subject: Re: [PATCH 1/2] dt-bindings: phy: imx8mq-usb: add phy tuning
 properties

Hi Rob, hi Krzysztof,

On 4/12/23 16:32, Johannes Zink wrote:
> Hi Rob,
> 
> On 4/12/23 15:39, Rob Herring wrote:
>> On Tue, Apr 11, 2023 at 04:22:37PM +0200, Johannes Zink wrote:
>>> Hi Krzystof,
>>>
>>> thank you for your explanations. As I'm still quite new to writing
>>> bindings, I still have some questions:
>>>
>>> On Fri, 2023-04-07 at 11:03 +0200, Krzysztof Kozlowski wrote:
>>>> On 05/04/2023 14:14, Johannes Zink wrote:
>>>>> Hi Krysztof,
>>>>>
>>>>> thanks for your review, please find my questions below.
>>>>>
>>>>> On Wed, 2023-04-05 at 13:51 +0200, Krzysztof Kozlowski wrote:
>>>>>> [snip]
>>>>>>>         A phandle to the regulator for USB VBUS.
>>>>>>> +  fsl,phy-tx-vref-tune:
>>>>>>> +    description:
>>>>>>> +      HS DC Voltage level adjustment
>>>>>>
>>>>>> "Level" in what units?
>>>>>>
>>>>>
>>>>> The datasheet just shows percent, ranging from -6 to +24%, in 2%
>>>>> increments. What unit would you suggest?
>>>>
>>>> percent
>>>> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml
>>>
>>> I am still a bit confused how to use this properly. How can I restrict
>>> the values to multiples of 2 in order to avoid illegal values?
>>>
>>> At the moment the only thing I could come up with is something like
>>>
>>> fsl,phy-tx-vref-tune-percent:
>>>    description: |
>>>      Adjusts the high-speed DC level voltage
>>>    $ref: /schemas/types.yaml#/definitions/int32
>>
>> Note that with standard unit suffixes, you don't need a type.
>>
>>>    minimum: -6
>>>    maximum: 24
>>>    default: 0
>>>
>>> Does something like this work? I am not quite sure if I am on the right
>>> track here, especially as this requires a signed int, of which I have
>>> not seen many examples so far.
>>
>> We'd have to change the type for -percent to signed. That's possible,
>> but for vendor specific properties there's not much advantage to use
>> standard units instead of just using the register values directly.
>>
> 
> I don't have any objections to that, this is pretty much what I sent in 
> my v1 patch <20230405112118.1256151-2-j.zink@...gutronix.de>, but 
> Krzysztof requested to change the vendor specific properties to use 
> property-units.
> 
> Would something along the lines of the st,trim-hs-current on 
> Documentation/devicetree/bindings/phy/phy-stm32-usbphyc.yaml be 
> acceptable (i.e. use an enum and annotate the meaning of the values in 
> the description)?
> 
> I will, nevertheless, try to make the descriptions a bit more verbose in 
> my v2 (wherever the datasheet gives me proper informations), as 
> Krzysztof requested.

gentle ping - any opinions on this? Shall I just send a V2 along the 
lines of the phy-stm32-usbphy.c?

Best regards
Johannes

> 
> Best regards
> Johannes
> 
>> Rob
>>
> 

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