linux-kernel - Re: [PATCH] arm64: dts: qcom: sc8280xp-x13s: Use the correct DP PHY compatible

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Message-ID: <CAA8EJpr=HQOs8Ho_s_34y0-krCHwq3MThMkUzhOkPVdOSMQ62A@mail.gmail.com>
Date:   Mon, 16 Oct 2023 12:10:18 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        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>,
        Johan Hovold <johan+linaro@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: qcom: sc8280xp-x13s: Use the correct DP PHY compatible

On Mon, 16 Oct 2023 at 12:01, Johan Hovold <johan@...nel.org> wrote:
>
> On Mon, Oct 16, 2023 at 11:51:33AM +0300, Dmitry Baryshkov wrote:
> > On Fri, 29 Sept 2023 at 19:03, Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
> > >
> > > The DP PHY needs different settings when an eDP display is used.
> > > Make sure these apply on the X13s.
> >
> > Could you please clarify, is it the same PHY type, just being
> > repurposed for eDP or is it a different PHY type?
>
> Same PHY, just different settings AFAIK.
>
> > If the former is the case (and the same PHY can be used for both DP
> > and eDP), it should carry the same compatible string and use software
> > mechanisms (e.g. phy_set_mode_ext()) to be programmed for the correct
> > operation mode.
>
> Possibly, but that's not how the current binding and implementation
> works:
>
>         6993c079cd58 ("dt-bindings: phy: qcom-edp: Add SC8280XP PHY compatibles")
>         2300d1cb24b3 ("phy: qcom: edp: Introduce support for DisplayPort")
>         3b7267dec445 ("phy: qcom: edp: Add SC8280XP eDP and DP PHYs")
>
>         https://lore.kernel.org/lkml/20220810040745.3582985-1-bjorn.andersson@linaro.org/
>
> And you'd still need to infer the mode from DT somehow.

If it is the same hardware block, it seems incorrect to have two
different compat entries. For example, for PCIe RC vs PCIe EP we
specify the PHY mode from the host controller driver.
I'd say, we need to fix the bindings for both DP/eDP controller and
the PHY.  See the `phy-mode` DT property for example.


-- 
With best wishes
Dmitry