linux-kernel - Re: [PATCH v12 4/4] arm64: dts: qcom: sc7280-herobrine: Add lpi pinmux properties for CRD 3.0/3.1

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Date:   Fri, 29 Apr 2022 09:10:06 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Matthias Kaehlcke <mka@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Srinivasa Rao Mandadapu <quic_srivasam@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        quic_rohkumar@...cinc.com,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Judy Hsiao <judyhsiao@...omium.org>,
        Venkata Prasad Potturu <quic_potturu@...cinc.com>
Subject: Re: [PATCH v12 4/4] arm64: dts: qcom: sc7280-herobrine: Add lpi
 pinmux properties for CRD 3.0/3.1

Hi,

On Thu, Apr 28, 2022 at 5:02 PM Matthias Kaehlcke <mka@...omium.org> wrote:
>
> On Wed, Apr 27, 2022 at 10:39:43PM +0530, Srinivasa Rao Mandadapu wrote:
> > Add LPASS LPI pinctrl properties, which are required for Audio
> > functionality on herobrine based platforms of rev5+
> > (aka CRD 3.0/3.1) boards.
> >
> > Signed-off-by: Srinivasa Rao Mandadapu <quic_srivasam@...cinc.com>
> > Co-developed-by: Venkata Prasad Potturu <quic_potturu@...cinc.com>
> > Signed-off-by: Venkata Prasad Potturu <quic_potturu@...cinc.com>
>
> I'm not super firm in pinctrl territory, a few maybe silly questions
> below.
>
> >  arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts | 84 +++++++++++++++++++++++
> >  1 file changed, 84 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts b/arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts
> > index deaea3a..dfc42df 100644
> > --- a/arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts
> > +++ b/arch/arm64/boot/dts/qcom/sc7280-herobrine-crd.dts
> > @@ -111,6 +111,90 @@ ap_ts_pen_1v8: &i2c13 {
> >   * - If a pin is not hooked up on Qcard, it gets no name.
> >   */
> >
> > +&lpass_dmic01 {
> > +     clk {
> > +             drive-strength = <8>;
> > +     };

Ugh, I've been distracted and I hadn't realized we were back to the
two-level syntax. Definitely not my favorite for all the reasons I
talked about [1]. I guess you took Bjorn's silence to my response to
mean that you should switch back to this way? :(

Bjorn: can you clarify?

[1] https://lore.kernel.org/r/CAD=FV=VicFiX6QkBksZs1KLwJ5x4eCte6j5RWOBPN+WwiXm2Cw@mail.gmail.com/

> > +};
> > +
> > +&lpass_dmic01_sleep {
> > +     clk {
> > +             drive-strength = <2>;
>
> Does the drive strength really matter in the sleep state, is the SoC actively
> driving the pin?

My understanding is that if a pin is left as an output in sleep state
that there is a slight benefit to switching it to drive-strength 2.


> > +             bias-disable;
>
> What should this be in active/default state? If I understand correctly
> after a transition from 'sleep' to 'default' this setting will remain,
> since the default config doesn't specify a setting for bias.

Your understanding matches mine but I haven't tested it and I remember
sometimes being surprised in this corner of pinmux before. I think
it's better to put the bias in the default state if it should be that
way all the time, or have a bias in both the default and sleep state
if they need to be different.