linux-kernel - Re: [PATCH] arm64: dts: qcom: sdm845-mtp: Add WCN3990 BT node

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Date:   Thu, 17 Jan 2019 13:55:59 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Balakrishna Godavarthi <bgodavar@...eaurora.org>
Subject: Re: [PATCH] arm64: dts: qcom: sdm845-mtp: Add WCN3990 BT node

On Thu 17 Jan 11:28 PST 2019, Matthias Kaehlcke wrote:

> On Wed, Jan 16, 2019 at 08:40:06PM -0800, Bjorn Andersson wrote:
[..]
> > +&qup_uart6_default {
> > +	pinmux {
> > +		pins = "gpio45", "gpio46", "gpio47", "gpio48";
> > +		function = "qup6";
> > +	};
> > +
> > +	ctsrx {
> > +		pins = "gpio45", "gpio48";
> > +		drive-strength = <2>;
> 
> CTS and RX are input signals, no need to configure drive strength in
> this case IIUC.
> 

Right, didn't think that far when I hacked this up.

> > +		bias-no-pull;
> 
> On another SDM845 based device we observe garbage on RX at
> initialization time, unless we enable a pull-up.
> 
> > +	};
> > +
> > +	rts {
> > +		pins = "gpio46";
> > +		drive-strength = <2>;
> > +		bias-pull-down;
> > +	};
> 
> On our device we don't configure a pull on the lines driven by the
> AP. I think a pull-down on RTS should be fine though since it matches
> the pull (during reset) on CTS of the BT module.
> 
> > +	tx {
> > +		pins = "gpio47";
> > +		drive-strength = <2>;
> > +		bias-pull-up;
> > +	};
> > +};
> 
> Similar to RTS, the pull matches the one on RXD of the BT module.
> 
> For reference, this is what we currently use on our device:
> 
> https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/1391888/3/arch/arm64/boot/dts/qcom/sdm845-cheza.dtsi
> 

Thanks, I will update the patch.

Regards,
Bjorn