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

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Message-ID: <Y3Jv4ePkPiKiG8wj@hovoldconsulting.com>
Date:   Mon, 14 Nov 2022 17:42:09 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.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 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.

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).

Johan