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

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Message-ID: <de3a426a-03e8-ed15-a9a1-bb300e776e5f@linaro.org>
Date:   Mon, 14 Nov 2022 15:07:41 +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 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.
>>>
>>
>> Thank you for your patch. There is something to discuss/improve.
>>
>>
>>> +
>>> +maintainers:
>>> +  - Vinod Koul <vkoul@...nel.org>
>>
>> Maybe you want to add also yourself?
> 
> Due to the lack of public documentation for these platforms and the
> amount of work involved in effectively reverse-engineering the
> corresponding details from random vendor-kernel trees, it's probably
> best to leave maintainence with Vinod who at least has access to some
> documentation.
> 
>>> +
>>> +description:
>>> +  The QMP PHY controller supports physical layer functionality for a number of
>>> +  controllers on Qualcomm chipsets, such as, PCIe, UFS and USB.
>>> +
>>> +  See also:
>>> +    - include/dt-bindings/dt-bindings/phy/phy.h
>>> +
>>> +properties:
>>> +  compatible:
>>> +    enum:
>>> +      - qcom,sc8280xp-qmp-usb43dp-phy
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  clocks:
>>> +    maxItems: 4
>>> +
>>> +  clock-names:
>>> +    items:
>>> +      - const: aux
>>> +      - const: ref
>>> +      - const: com_aux
>>> +      - const: usb3_pipe
>>> +
>>> +  power-domains:
>>> +    maxItems: 1
>>> +
>>> +  resets:
>>> +    maxItems: 2
>>> +
>>> +  reset-names:
>>> +    items:
>>> +      - const: phy
>>> +      - const: common
>>> +
>>> +  vdda-phy-supply: true
>>> +
>>> +  vdda-pll-supply: true
>>> +
>>> +  "#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.

> doesn't use these names, but that's a Linux-specific implementation
> detail.
> 
> I noticed that several bindings leave the clock indexes unspecified, or
> have header files defining some or all of them. I first added a QMP
> header but that seemed like overkill, especially if we'd end up with
> one header per SoC (cf. the GCC headers) due to (known and potential)
> platform differences.

Headers for the names? I do not recall such but that does not seem right.

> 
> On the other hand reproducing this list in each node is admittedly a bit
> redundant.
> 
> Shall I add back a shared header for all PHYs handled by this driver
> (another implementation detail) even if this could eventually lead to
> describing clocks not supported by a particular SoC (so such constraints
> would still need to be described by the binding somehow):
> 
> 	/* QMP clocks */
> 	#define QMP_USB3_PIPE_CLK	0
> 	#define QMP_DP_LINK_CLK		1
> 	#define QMP_DP_VCO_DIV_CLK	2

What are these about? To remind - we talk about names of clocks this
device creates. The output names. Whatever IDs you have are not related
to the names.


Best regards,
Krzysztof