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: <20200903161434.GI3419728@google.com>
Date:   Thu, 3 Sep 2020 09:14:34 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     satya priya <skakit@...eaurora.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        gregkh@...uxfoundation.org, Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, akashast@...eaurora.org,
        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

On Thu, Sep 03, 2020 at 08:34:56PM +0530, satya priya wrote:
> Configure no-pull for CTS, as this is driven by BT do not specify any pull
> in order to not conflict with BT pulls.
> 
> Remove output-high from CTS and TX as this is not really required. During
> bringup to fix transfer failures this was added to match with console uart
> settings. Probably some boot loader config was missing then. As it is
> working fine now, remove it.

You might want to revisit the 'output-high' settings for the IDP console
uart too. I still think this shouldn't do anything on an input pin that
isn't configured as GPIO. Specifically this combination seems silly:

  bias-pull-down;
  output-high;

> Signed-off-by: satya priya <skakit@...eaurora.org>
> Reviewed-by: Akash Asthana <akashast@...eaurora.org>
> ---
> Changes in V4:
>  - This is newly added in V4 to separate the improvements in pin settings
>    and wakeup related changes.
> 
>  arch/arm64/boot/dts/qcom/sc7180-idp.dts | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> index d8b5507..cecac3e 100644
> --- 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;
> +		bias-disable;
>  	};
>  
>  	pinconf-rts {
> -		/* We'll drive 39 (RTS), so no pull */
> +		/* We'll drive RTS, so no pull */
>  		pins = "gpio39";
>  		drive-strength = <2>;
>  		bias-disable;
>  	};
>  
>  	pinconf-tx {
> -		/* We'll drive 40 (TX), so no pull */
> +		/* We'll drive TX, so no pull */
>  		pins = "gpio40";
>  		drive-strength = <2>;
>  		bias-disable;
> -		output-high;
>  	};
>  
>  	pinconf-rx {
>  		/*
> -		 * Configure a pull-up on 41 (RX). This is needed to avoid
> +		 * Configure a pull-up on RX. This is needed to avoid
>  		 * garbage data when the TX pin of the Bluetooth module is
>  		 * in tri-state (module powered off or not driving the
>  		 * signal yet).

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>