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

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Message-ID: <20200819161311.GF2995789@google.com>
Date:   Wed, 19 Aug 2020 09:13:11 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     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 Wed, Aug 19, 2020 at 07:19:25PM +0530, skakit@...eaurora.org wrote:
> On 2020-08-17 23:31, Matthias Kaehlcke wrote:
> > 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?
> > 
> 
> The previous config was incorrect, so we corrected it to match the pull of
> BT.

The pull config of the BT controller varies depending on its state, could
you clarify which state you intend to match?

> 
> > >  		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.
> 
> The rationale for RTS is that we don't want it to be floating and want to
> make sure that it is pulled down, to receive bytes. Will modify the comment
> mentioning the same.

Could you clarify what you mean with "to receive bytes"?

Thanks

Matthias