linux-kernel - Re: [PATCH v5 4/4] arm64: dts: qcom: thinkpad-x13s: Add bluetooth

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Message-ID: <ZArXx3g1oGb6GSVY@hovoldconsulting.com>
Date:   Fri, 10 Mar 2023 08:09:59 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Steev Klimaszewski <steev@...i.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Sven Peter <sven@...npeter.dev>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        Mark Pearson <markpearson@...ovo.com>
Subject: Re: [PATCH v5 4/4] arm64: dts: qcom: thinkpad-x13s: Add bluetooth

On Thu, Mar 09, 2023 at 02:07:58PM -0600, Steev Klimaszewski wrote:
> On Thu, Mar 9, 2023 at 11:24 AM Johan Hovold <johan@...nel.org> wrote:
> > On Wed, Feb 08, 2023 at 08:09:16PM -0600, Steev Klimaszewski wrote:

> > > +     uart2_state: uart2-state {
> >
> > Rename this one too:
> >
> >         uart2_default: uart2-default-state
> >
> > > +             cts-pins {
> > > +                     pins = "gpio122";
> >
> > This should be gpio121 (gpio122 is rts).
> >
> 
> You are right that it should be... however... if I actually set it to
> be 121.... bluetooth doesn't actually come up/work?

I'm running with this fixed locally and it's working here.

Not muxing the cts-pin should break flow control (e.g. the host will
send data regardless of if the device signals that it's ready to receive
it).

> > > +                     function = "qup2";
> > > +                     bias-disable;
> >
> > Don't we need a pull-down on this one to avoid a floating input when the
> > module is powered down?
>
> Maybe?  I don't have access to the schematics or anything so I was
> going with the best guess based on what worked by poking and prodding.
> Will try this.

There are no external resistors and most of the Qualcomm boards with
these Bluetooth modules appear to enable the internal pull-down on cts.

But there are also two boards that recently switched to bias-bus-hold:

	3d0e375bae55 ("arm64: dts: qcom: sc7280-qcard: Configure CTS pin to bias-bus-hold for bluetooth")

to avoid leakage. Perhaps that's what we want here too.

Johan