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

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Date:   Tue, 15 Nov 2022 15:22:56 +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 Tue, Nov 15, 2022 at 09:12:54AM +0100, Krzysztof Kozlowski wrote:
> On 14/11/2022 18:08, Johan Hovold wrote:
> >>
> >> 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?
> 
> No, you don't have to. I just got impression that future devices will
> bring so many changes that anyway you will end up with per-SoC defines.
> 
> > 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
> 
> The names are just a names, you can even use QMP_SC7180_* on SC8280XP.
> You can skip the SoC part and have something shared. We already have
> such patterns - although maybe more often for outside components (like
> PMICs). The differences are:
> 1. For per-SoC name it's quite obvious which clock is supported on fiven
> SoC,
> 2. With shared names, you should document somewhere mapping between
> supported clocks and SoCs. Also what to do if new device comes with 10
> new clocks entirely different - re-use/map existing defines or add
> completely new set of 10 of them?

Ok, thanks. I'll go with a common prefix per PHY type for now, and we
can worry about hypothetical hardware revisions later.

I'll use a "QMP_USB43DP_" prefix for the new SC8280XP binding, which can
be reused also for the older SoCs with USB3-DP PHYs if/when we convert
them as their indexes will be a subset of the SC8280XP ones:

	/* QMP USB4-USB3-DP clocks */
	#define QMP_USB43DP_USB3_PIPE_CLK	0
	#define QMP_USB43DP_DP_LINK_CLK		1
	#define QMP_USB43DP_DP_VCO_DIV_CLK	2

Since I'm adding a new header anyway, I decided to go with dedicated
indexes also for the PHY selection (instead of using the PHY_TYPE
defines):

	/* QMP USB4-USB3-DP PHYs */
	#define QMP_USB43DP_USB3_PHY		0
	#define QMP_USB43DP_DP_PHY		1

I'll add these to a common dt-bindings/phy/phy-qcom-qmp.h header so that
it can be used also for the UFS clocks (with a "QMP_UFS_" prefix).

Johan