linux-kernel - Re: [PATCH 03/15] dt-bindings: clock: qcom,dispcc-sm6125: Require GCC PLL0 DIV clock

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Message-ID: <dp2ucgmql2jff52nbxti2hwjchtgjkbrwcgpx3p7ruodz7adnj@635pcqr6fv4x>
Date:   Mon, 26 Jun 2023 16:26:24 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Krishna Manikandan <quic_mkrishn@...cinc.com>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-clk@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, Lux Aliaga <they@...t.lgbt>
Subject: Re: [PATCH 03/15] dt-bindings: clock: qcom,dispcc-sm6125: Require
 GCC PLL0 DIV clock

On 2023-06-26 11:43:39, Konrad Dybcio wrote:
> On 25.06.2023 21:48, Marijn Suijten wrote:
> > On 2023-06-24 03:45:02, Konrad Dybcio wrote:
> >> On 24.06.2023 02:41, Marijn Suijten wrote:
> >>> The "gcc_disp_gpll0_div_clk_src" clock is consumed by the driver, will
> >>> be passed from DT, and should be required by the bindings.
> >>>
> >>> Fixes: 8397c9c0c26b ("dt-bindings: clock: add QCOM SM6125 display clock bindings")
> >>> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> >>> ---
> >> Ideally, you'd stick it at the bottom of the list, as the items: order
> >> is part of the ABI
> > 
> > This isn't an ABI break, as this driver nor its bindings require/declare
> > a fixed order: they declare a relation between clocks and clock-names.
> Bindings describe the ABI, drivers implement compliant code flow.

That is how bindings are supposed to be...  However typically the driver
is written/ported first and then the bindings are simply created to
reflect this, and sometimes (as is the case with this patch)
incorrectly.

That, together with a lack of DTS and known-working device with it
(which is why I'm submitting driver+bindings+dts in one series now!)
makes us shoot ourselves in the foot by locking everyone into an ABI
that makes no sense.

> > This orders the GCC clock just like other dispccs.  And the previous
> > patch dropped the unused cfg_ahb_clk from the bindings, so all bets are
> > off anyway.
> Thinking about it again, the binding has not been consumed by any upstream
> DT to date, so it should (tm) be fine to let it slide..

Exactly, I hope/doubt anyone was already using these incomplete
bindings.  And again: the ABI here is the name->phandle mapping, the
order Does Not Matter™.  So I hope we can let it slide (otherwise the
previous patch shouldd have been NAK'ed as well??)

(Unless you are SM6115 which uses index-based mapping and does not
 define clock-names at all)

- Marijn

> Konrad
> > 
> > - Marijn
> > 
> >>
> >> Konrad
> >>>  Documentation/devicetree/bindings/clock/qcom,dispcc-sm6125.yaml | 4 ++++
> >>>  1 file changed, 4 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/clock/qcom,dispcc-sm6125.yaml b/Documentation/devicetree/bindings/clock/qcom,dispcc-sm6125.yaml
> >>> index 2acf487d8a2f..11ec154503a3 100644
> >>> --- a/Documentation/devicetree/bindings/clock/qcom,dispcc-sm6125.yaml
> >>> +++ b/Documentation/devicetree/bindings/clock/qcom,dispcc-sm6125.yaml
> >>> @@ -23,6 +23,7 @@ properties:
> >>>    clocks:
> >>>      items:
> >>>        - description: Board XO source
> >>> +      - description: GPLL0 div source from GCC
> >>>        - description: Byte clock from DSI PHY0
> >>>        - description: Pixel clock from DSI PHY0
> >>>        - description: Pixel clock from DSI PHY1
> >>> @@ -32,6 +33,7 @@ properties:
> >>>    clock-names:
> >>>      items:
> >>>        - const: bi_tcxo
> >>> +      - const: gcc_disp_gpll0_div_clk_src
> >>>        - const: dsi0_phy_pll_out_byteclk
> >>>        - const: dsi0_phy_pll_out_dsiclk
> >>>        - const: dsi1_phy_pll_out_dsiclk
> >>> @@ -65,12 +67,14 @@ examples:
> >>>        compatible = "qcom,sm6125-dispcc";
> >>>        reg = <0x5f00000 0x20000>;
> >>>        clocks = <&rpmcc RPM_SMD_XO_CLK_SRC>,
> >>> +               <&gcc GCC_DISP_GPLL0_DIV_CLK_SRC>,
> >>>                 <&dsi0_phy 0>,
> >>>                 <&dsi0_phy 1>,
> >>>                 <&dsi1_phy 1>,
> >>>                 <&dp_phy 0>,
> >>>                 <&dp_phy 1>;
> >>>        clock-names = "bi_tcxo",
> >>> +                    "gcc_disp_gpll0_div_clk_src",
> >>>                      "dsi0_phy_pll_out_byteclk",
> >>>                      "dsi0_phy_pll_out_dsiclk",
> >>>                      "dsi1_phy_pll_out_dsiclk",
> >>>