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From:   Stephen Boyd <swboyd@chromium.org>
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Date:   Wed, 13 Oct 2021 15:14:20 -0500
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Subject: Re: [PATCH v2] arm64: dts: qcom: sc7280: Add bluetooth node on SC7280
To:     bgodavar@codeaurora.org
Cc:     bjorn.andersson@linaro.org, johan.hedberg@gmail.com,
        marcel@holtmann.org, mka@chromium.org,
        linux-kernel@vger.kernel.org, linux-bluetooth@vger.kernel.org,
        hemantg@codeaurora.org, linux-arm-msm@vger.kernel.org,
        pharish@codeaurora.org, rjliao@codeaurora.org,
        hbandi@codeaurora.org, saluvala@codeaurora.org,
        abhishekpandit@chromium.org
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Quoting bgodavar@codeaurora.org (2021-10-12 22:30:50)
> On 2021-10-12 22:54, Stephen Boyd wrote:
> > Quoting Balakrishna Godavarthi (2021-10-12 06:01:38)
> >> diff --git a/arch/arm64/boot/dts/qcom/sc7280-idp.dtsi
> >> b/arch/arm64/boot/dts/qcom/sc7280-idp.dtsi
> >> index 272d5ca..09adc802 100644
> >> --- a/arch/arm64/boot/dts/qcom/sc7280-idp.dtsi
> >> +++ b/arch/arm64/boot/dts/qcom/sc7280-idp.dtsi
> >> +               compatible = "qcom,wcn6750-bt";
> >> +               pinctrl-names = "default";
> >> +               pinctrl-0 = <&bt_en_default>;
> >> +               enable-gpios = <&tlmm 85 GPIO_ACTIVE_HIGH>;
> >> +               swctrl-gpios = <&tlmm 86 GPIO_ACTIVE_HIGH>;
> >
> > Is there any pinctrl config for gpio 86?
> >
> [Bala]: This is input GPIO to apps, BT SOC will handle configurations.

Ok. So there should be some pinctrl stating that the function is "gpio"
and the biasing is probably bias-disable. The BT SOC will handle setting
any pull, either up or down?

>
> >> +               vddaon-supply = <&vreg_s7b_0p9>;
> >> +               vddbtcxmx-supply = <&vreg_s7b_0p9>;
> >> +               vddrfacmn-supply = <&vreg_s7b_0p9>;
> >> +               vddrfa0p8-supply = <&vreg_s7b_0p9>;
> >> +               vddrfa1p7-supply = <&vreg_s1b_1p8>;
> >> +               vddrfa1p2-supply = <&vreg_s8b_1p2>;
> >> +               vddrfa2p2-supply = <&vreg_s1c_2p2>;
> >> +               vddasd-supply = <&vreg_l11c_2p8>;
> >> +               max-speed = <3200000>;
> >> +       };
> >>  };
> >>
> >>  /* PINCTRL - additions to nodes defined in sc7280.dtsi */
> >> @@ -504,6 +521,14 @@
> >>                  */
> >>                 bias-pull-up;
> >>         };
> >> +
> >> +       bt_en_default: bt_en_default {
> >
> > bt_en: bt-en {
> >
> > Node names shouldn't have underscores and 'default' is redundant.
> >
> [Bala]: will update in next patch.
>
> >> +               pins = "gpio85";
> >> +               function = "gpio";
> >> +               drive-strength = <2>;
> >> +               output-low;
> >> +               bias-pull-down;
> >
> > Why is there a pull down on an output gpio? Shouldn't this be
> > bias-disable?
> >
>
> [Bala]: BT_EN pin is OP of apps and input to BT SoC.
> by default we want the state of BT_EN to be low. so used pull down
> instead of bias-disable

The pin state will be low because of the 'output-low' property.

> as AFAIK bias-disable may trigger a tristate on BT_EN pin, which may
> trigger BT SoC enable
> if it is not actually triggered.

Is the pin ever "turned around" and made an input? If not then it will
be output and be driving low until the enable-gpios is set to output
active. The pull down is probably wasting power when the pin is being
driven either high or low.