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From:   Doug Anderson <dianders@chromium.org>
Date:   Mon, 25 Apr 2022 14:18:39 -0700
Message-ID: <CAD=FV=WmVK3wTQf_EAxSi0WPXedSFGCsKdyqRnHsskmMYTHDQA@mail.gmail.com>
Subject: Re: [PATCH 1/2] dt-bindings: msm/dp: List supplies in the bindings
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Rob Clark <robdclark@chromium.org>,
        Rob Herring <robh+dt@kernel.org>,
        Vinod Koul <vkoul@kernel.org>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        linux-phy@lists.infradead.org,
        dri-devel <dri-devel@lists.freedesktop.org>,
        freedreno <freedreno@lists.freedesktop.org>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        Sankeerth Billakanti <quic_sbillaka@quicinc.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        quic_kalyant <quic_kalyant@quicinc.com>,
        Kuogee Hsieh <quic_khsieh@quicinc.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>,
        Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
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Hi,

On Mon, Apr 25, 2022 at 2:14 PM Stephen Boyd <swboyd@chromium.org> wrote:
>
> Quoting Douglas Anderson (2022-04-25 14:06:42)
> > We're supposed to list the supplies in the dt bindings but there are
> > none in the DP controller bindings. Looking at the Linux driver and
> > existing device trees, we can see that two supplies are expected:
> > - vdda-0p9-supply
> > - vdda-1p2-supply
> >
> > Let's list them both in the bindings. Note that the datasheet for
> > sc7280 doesn't describe these supplies very verbosely. For the 0p9
> > supply, for instance, it says "Power for eDP 0.9 V circuits". This
> > this is obvious from the property name, we don't bother cluttering the
> > bindings with a description.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> >  .../devicetree/bindings/display/msm/dp-controller.yaml      | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
> > index cd05cfd76536..dba31108db51 100644
> > --- a/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
> > +++ b/Documentation/devicetree/bindings/display/msm/dp-controller.yaml
> > @@ -76,6 +76,9 @@ properties:
> >    "#sound-dai-cells":
> >      const: 0
> >
> > +  vdda-0p9-supply: true
> > +  vdda-1p2-supply: true
> > +
> >    ports:
> >      $ref: /schemas/graph.yaml#/properties/ports
> >      properties:
> > @@ -137,6 +140,9 @@ examples:
> >
> >          power-domains = <&rpmhpd SC7180_CX>;
> >
> > +        vdda-0p9-supply = <&vdda_usb_ss_dp_core>;
>
> Having 'a' in 'vdda' typically means 'analog' for 'analog' circuits, so
> I'd expect this to only matter for the phy that contains the analog
> circuitry. It would be great to remove the regulator code from
> drivers/gpu/drm/msm/dp/dp_power.c and move the regulator_set_load() call
> to the phy driver if possible. Hopefully qcom folks can help clarify
> here.

Interesting. Oddly enough, the sc7280 datasheet doesn't list the "_A".
It calls these "VDD_VREF_0P9" and "VDD_VREF_1P2". However, on the
schematic in front of me someone labeled these pins on the sc7280 with
the "A". ...and the driver looks for a supply with the "a". :-/

It would be good to get clarification from someone with better information.

-Doug