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

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Date:   Mon, 14 Nov 2022 19:51:31 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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>,
        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 19:42, Johan Hovold wrote:
> On Mon, Nov 14, 2022 at 07:14:48PM +0300, Dmitry Baryshkov wrote:
>> On 14/11/2022 18:38, Johan Hovold wrote:
>>> On Mon, Nov 14, 2022 at 06:19:25PM +0300, Dmitry Baryshkov wrote:
>>>> On 14/11/2022 17:18, 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:
>>>
>>>>>>> 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.
>>>
>>>>>>> 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
>>>>
>>>> Maybe QMP_COMBO_USB3_PIPE_CLK, QMP_COMBO_DP_LINK_CLK,
>>>> QMP_COMBO_DP_VCO_DIV_CLK?
>>>
>>> "COMBO" is just the name of the Linux driver and does not belong in the
>>> binding.
>>
>> We do not have any standard (iow, coming from the docs) name, so we can
>> invent it on our own.
> 
> I still think the naming should reflect the hardware and not the Linux
> implementation if this is going into the binding.

Well, I always viewed docs as

> 
> And the USB4_USB3_DP defines are going to be a superset of USB3_DP (as
> far we know know).
> 
>>>> I'll then extend this header with QMP_UFS_RX_SYMBOL_0_CLK
>>>> QMP_UFS_RX_SYMBOL_1_CLK and QMP_UFS_TX_SYMBOL_0_CLK.
>>>
>>> Yeah, I had those in mind when creating the header and using a generic
>>> QMP prefix (even if I didn't end up using the header in v1).
>>>
>>> This could just be mapping of (arbitrary) QMP indexes to clocks and we
>>> use it for USB3, DP, UFS and later also USB4.
>>>
>>> This will however mean that the indexes are not necessarily zero-based
>>> and consecutive for a specific SoC and PHY. But that's perhaps a
>>> non-issue (cf. the PHY_TYPE defines).
>>
>> Ugh. Please, no. We have symbol clocks for UFS PHY, USB+DP clocks for
>> USB+DP PHY, but let's not go for the unified clocks index definition.
> 
> Yeah, this is the kind of issues I wanted to avoid by not using a per
> SoC header for three clocks which will almost always use the same
> indexes.
> 
> Because how can you be sure that your unified per-PHY type defines will
> never have to be amended? Or some index left out?
> 
> The only way then is to have per-SoC defines which is a pain to
> maintain (just consider that driver mapping table when some odd SoC
> shows up).

My vote is definitely against a per-SoC defines.

> 
> Johan

-- 
With best wishes
Dmitry