linux-kernel - Re: [PATCH V4 2/4] arm64: dts: qcom: sc7180: Improve the pin config settings for CTS and TX

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Date:   Wed, 9 Sep 2020 14:28:01 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     satya priya <skakit@...eaurora.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Akash Asthana <akashast@...eaurora.org>,
        Roja Rani Yarubandi <rojay@...eaurora.org>,
        msavaliy@....qualcomm.com
Subject: Re: [PATCH V4 2/4] arm64: dts: qcom: sc7180: Improve the pin config
 settings for CTS and TX

Hi,

On Thu, Sep 3, 2020 at 8:07 AM satya priya <skakit@...eaurora.org> wrote:
>
> --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> @@ -474,32 +474,30 @@
>  &qup_uart3_default {
>         pinconf-cts {
>                 /*
> -                * Configure a pull-down on 38 (CTS) to match the pull of
> -                * the Bluetooth module.
> +                * Configure no-pull on CTS. As this is driven by BT, do not
> +                * specify any pull in order to not conflict with BT pulls.
>                  */
>                 pins = "gpio38";
> -               bias-pull-down;
> -               output-high;

Weird, how did that output-high sneak in there?  Glad it's going away.


> +               bias-disable;

I'm not convinced that the removal of the pul is the correct thing
here.  Specifically for the rx line the comment makes the argument
that if we power off the Bluetooth module then it will stop driving
this pin.  In that case if we remove the pull here then the line will
be floating and that can cause some extra power consumption as the
line floats between different logic levels.  Do you really need to
remove this pull?

Same comment for the next patch where you add the sleep settings.


-Doug