linux-kernel - RE: [PATCH 1/2] dt-bindings: msm/dp: List supplies in the bindings

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Date:   Thu, 5 May 2022 18:02:36 +0000
From:   Sankeerth Billakanti <sbillaka@....qualcomm.com>
To:     Doug Anderson <dianders@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>
CC:     "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        Rob Clark <robdclark@...omium.org>,
        Rob Herring <robh+dt@...nel.org>,
        Vinod Koul <vkoul@...nel.org>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "linux-phy@...ts.infradead.org" <linux-phy@...ts.infradead.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "Kalyan Thota (QUIC)" <quic_kalyant@...cinc.com>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] dt-bindings: msm/dp: List supplies in the bindings

Hi Doug,

>>
>> 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@...omium.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.ya
>> > +++ ml
>> > @@ -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

Our internal power grid documents list the regulators as VDD_A_*_1P2 and VDD_A_*_0P9
for all the platforms.

So, as a practice, we put the same name in the DT files. Hence,

Reviewed-by: Sankeerth Billakanti <quic_sbillaka@...cinc.com>

Thank you,
Sankeerth