linux-kernel - Re: [PATCH 02/14] dt-bindings: phy: qcom,qmp-usb3-dp: fix sc8280xp bindings

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Message-ID: <efd412d0-7411-8b0b-4700-9e183a592048@linaro.org>
Date:   Mon, 14 Nov 2022 17:39:26 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Vinod Koul <vkoul@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/14] dt-bindings: phy: qcom,qmp-usb3-dp: fix sc8280xp
 bindings

On 14/11/2022 17:32, Johan Hovold wrote:
> On Mon, Nov 14, 2022 at 04:49:37PM +0100, Krzysztof Kozlowski wrote:
>> On 14/11/2022 15:18, Johan Hovold wrote:
>>> On Mon, Nov 14, 2022 at 03:07:41PM +0100, Krzysztof Kozlowski wrote:
>>>> On 14/11/2022 14:27, Johan Hovold wrote:
>>>>> On Fri, Nov 11, 2022 at 04:17:29PM +0100, Krzysztof Kozlowski wrote:
>>>>>> On 11/11/2022 10:24, Johan Hovold wrote:
>>>>>>> The current QMP USB3-DP PHY bindings are based on the original MSM8996
>>>>>>> binding which provided multiple PHYs per IP block and these in turn were
>>>>>>> described by child nodes.
>>>
>>>>>>> +  "#clock-cells":
>>>>>>> +    const: 1
>>>>>>> +
>>>>>>> +  clock-output-names:
>>>>>>> +    items:
>>>>>>> +      - const: usb3_pipe
>>>>>>> +      - const: dp_link
>>>>>>> +      - const: dp_vco_div
>>>>>>
>>>>>> Why defining here fixed names? The purpose of this field is to actually
>>>>>> allow customizing these - at least in most cases. If these have to be
>>>>>> fixed, then driver should just instantiate these clocks with such names,
>>>>>> right?
>>>>>
>>>>> I'm only using these names as documentation of the indexes. The driver
>>>>
>>>> What do you mean by documentation of indexes? You require these specific
>>>> entries and do not allow anything else.
>>>
>>> I'm using this property as documentation of the valid indexes that can
>>> be used when referring to clocks provided by this device.
>>>
>>> There are currently three and the mapping is described by the
>>> 'clock-output-names' property.
>>
>> That's not the purpose of this property. Drop it then. The names do not
>> define the ABI and do not document it, actually. You require now that
>> every DTB, if providing clock-output-names, will have exactly such names
>> instead of having fixed IDs. DTBs are not for defining the ABI.
> 
> Fair enough, I'll drop it. But there doesn't seem to be a good way to
> describe the indexes currently and most bindings simply ignore to do so.
> 
> So what is the preference then? Just leave things undocumented, listing
> indexes in a free-text 'description', or adding a free-text reference to
> a binding header file and using those define names in a free-text
> 'description'?

Either 2 or 3. Several bindings for small number of constants choose
option 2.

> 
> And if going with the last option, does this mean that every SoC and PHY
> type needs its own header for those three clocks or so to avoid having
> a common dumping ground header file where indexes will not necessarily
> be 0-based and consecutive.

phy-qcom-qmp-combo.c has one qcom_qmp_dp_clks_hw_get(), so why would you
have many of header files?

Best regards,
Krzysztof