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 18:08:18 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.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 Mon, Nov 14, 2022 at 05:56:21PM +0100, Krzysztof Kozlowski wrote:
> On 14/11/2022 17:48, Johan Hovold wrote:
> > On Mon, Nov 14, 2022 at 05:39:26PM +0100, Krzysztof Kozlowski wrote:
> >> On 14/11/2022 17:32, Johan Hovold wrote:
> > 
> >>> 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.
> > 
> > Ok, we have three now, but USB4 will bump this to ten or so.
> 
> Then probably header file is the way to go.
> 
> >  
> >>> 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?
> > 
> > We don't know what kind of clock outputs later revisions of these PHYs
> > will have. The only way to guarantee 0-based consecutive indexes appears
> > to be to use per-SoC defines (e.g. as for the GCC bindings).
> 
> Which is also fine. I don't understand still why it is a problem - even
> if you have multiple files, one for each SoC/phy. If USB4 brings here 10
> more clocks and other SoCs/phys might bring many more options, then what
> else can you do? Grow the binding file with big text-based mapping of
> IDs? It's not a viable solution. Header or headers is the only
> maintainable way for such cases.

So then we must add per-SoC (and PHY type) headers even if we can
possibly reuse defines from one platform for another as long as they
appear to be similar enough? For example, using a "SC7180_USB3_DP" infix
for the current platforms and add a new series of indexes for SC8280XP:

	QMP_SC7180_USB3_DP_USB3_PIPE			0
	QMP_SC7180_USB3_DP_DP_LINK			1
	QMP_SC7180_USB3_DP_DP_VCO_DIV			2

	QMP_SC8280XP_USB4_USB3_DP_USB3_PIPE		0
	QMP_SC8280XP_USB4_USB3_DP_DP_LINK		1
	QMP_SC8280XP_USB4_USB3_DP_DP_VCO_DIV		2
	QMP_SC8280XP_USB4_USB3_DP_USB4_PCIE_PIPE	3
	...
	QMP_SC8280XP_USB4_USB3_DP_USB4_RX1		9

Johan