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

[Johan Hovold <johan@kernel.org>]

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@kernel.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