linux-kernel - Re: [PATCH V2 2/3] arm64: dts: qcom: sc7180: Add sleep pin ctrl for BT uart

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Date:   Mon, 17 Aug 2020 11:01:58 -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 V2 2/3] arm64: dts: qcom: sc7180: Add sleep pin ctrl for
 BT uart

On Fri, Jul 24, 2020 at 09:28:01AM +0530, satya priya wrote:
> Add sleep pin ctrl for BT uart, and also change the bias
> configuration to match Bluetooth module.
> 
> Signed-off-by: satya priya <skakit@...eaurora.org>
> ---
> Changes in V2:
>  - This patch adds sleep state for BT UART. Newly added in V2.
> 
>  arch/arm64/boot/dts/qcom/sc7180-idp.dts | 42 ++++++++++++++++++++++++++++-----
>  1 file changed, 36 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sc7180-idp.dts b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> index 26cc491..bc919f2 100644
> --- a/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> +++ b/arch/arm64/boot/dts/qcom/sc7180-idp.dts
> @@ -469,20 +469,50 @@
>  
>  &qup_uart3_default {
>  	pinconf-cts {
> -		/*
> -		 * Configure a pull-down on 38 (CTS) to match the pull of
> -		 * the Bluetooth module.
> -		 */
> +		/* Configure no pull on 38 (CTS) to match Bluetooth module */

Has the pull from the Bluetooth module been removed or did the previous config
incorrectly claim that the Bluetooth module has a pull-down?

>  		pins = "gpio38";
> +		bias-disable;
> +	};
> +
> +	pinconf-rts {
> +		/* We'll drive 39 (RTS), so configure pull-down */
> +		pins = "gpio39";
> +		drive-strength = <2>;
>  		bias-pull-down;
> +	};
> +
> +	pinconf-tx {
> +		/* We'll drive 40 (TX), so no pull */

The rationales for RTS and TX contradict each other. According to the comment
the reason to configure a pull-down on RTS is that it is driven by the host.
Then for TX the reason to configure no pull is that it is driven by the host.

Please make sure the comments *really* describe the rationale, otherwise they
are just confusing.