linux-kernel - Re: [PATCH] arm64: dts: sc7180: Add board regulators for MIPI camera trogdor boards

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Date:   Wed, 15 Dec 2021 20:43:21 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH] arm64: dts: sc7180: Add board regulators for MIPI camera
 trogdor boards

Quoting Matthias Kaehlcke (2021-12-15 18:31:41)
> On Tue, Dec 14, 2021 at 04:36:38PM -0800, Stephen Boyd wrote:
> > diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> > index d4f4441179fc..1dd8e35093a8 100644
> > --- a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> > @@ -113,6 +113,40 @@ src_vph_pwr: src-vph-pwr-regulator {
> >               vin-supply = <&ppvar_sys>;
> >       };
> >
> > +     pp1800_uf_cam: pp1800-uf-cam-regulator {
> > +             compatible = "regulator-fixed";
> > +             regulator-name = "pp1800_uf_cam";
> > +             status = "disabled";
> > +
> > +             regulator-min-microvolt = <1800000>;
> > +             regulator-max-microvolt = <1800000>;
> > +
> > +             gpio = <&tlmm 6 GPIO_ACTIVE_HIGH>;
> > +             enable-active-high;
> > +             pinctrl-names = "default";
> > +             pinctrl-0 = <&uf_cam_en>;
> > +
> > +             vin-supply = <&pp1800_ldo>;
> > +             regulator-enable-ramp-delay = <1000>;
> > +     };
> > +
> > +     pp1800_wf_cam: pp1800-wf-cam-regulator {
> > +             compatible = "regulator-fixed";
> > +             regulator-name = "pp1800_wf_cam";
> > +             status = "disabled";
> > +
> > +             regulator-min-microvolt = <1800000>;
> > +             regulator-max-microvolt = <1800000>;
> > +
> > +             gpio = <&tlmm 7 GPIO_ACTIVE_HIGH>;
> > +             enable-active-high;
> > +             pinctrl-names = "default";
> > +             pinctrl-0 = <&wf_cam_en>;
> > +
> > +             vin-supply = <&pp1800_ldo>;
> > +             regulator-enable-ramp-delay = <1000>;
> > +     };
> > +
>
> Shouldn't 'pp1800_ldo' be defined before these ("FIXED REGULATORS
> - parents above children")?

Good catch! Fixed it.

>
> I suggest to move these two below the top level regulators, i.e.
> somwhere after pp3300_a (probably pp3300_a and pp5000_a should be
> swapped, but that's beyond the scope of this patch).
>
> >       pp5000_a: pp5000-a-regulator {
> >               compatible = "regulator-fixed";
> >               regulator-name = "pp5000_a";
> > @@ -1517,4 +1611,32 @@ pinconf-sd-cd {
> >                       drive-strength = <2>;
> >               };
> >       };
> > +
> > +     uf_cam_en: uf-cam-en {
> > +             pinmux {
> > +                     pins = "gpio6";
> > +                     function = "gpio";
> > +             };
> > +
> > +             pinconf {
> > +                     pins = "gpio6";
> > +                     drive-strength = <2>;
> > +                     /* External pull down */
>
> Is there actually an external pull down?

My understanding is that there's an internal pull down in the LDO so
while it isn't exactly "external" in the sense there's a pull down on
the net via a resistor, there's still a pull down that you can't see in
the schematic in the IC.