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

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Message-ID: <010101747810c24f-a169785b-0866-4932-a24e-80ff53393de2-000000@us-west-2.amazonses.com>
Date:   Thu, 10 Sep 2020 12:49:58 +0000
From:   skakit@...eaurora.org
To:     Doug Anderson <dianders@...omium.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 Doug,

On 2020-09-10 02:58, Doug Anderson wrote:
> 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?
> 

Okay, will keep the pull-down back for CTS.

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