linux-kernel - Re: [PATCH v2 1/2] dt-bindings: pinctrl: qcom: sc7280: Add compatible string for adsp based platforms

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Date:   Fri, 3 Jun 2022 12:19:11 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Srinivasa Rao Mandadapu <quic_srivasam@...cinc.com>
Cc:     Stephen Boyd <swboyd@...omium.org>, agross@...nel.org,
        alsa-devel@...a-project.org, bgoswami@...cinc.com,
        bjorn.andersson@...aro.org, broonie@...nel.org,
        devicetree@...r.kernel.org, judyhsiao@...omium.org,
        lgirdwood@...il.com, linux-arm-msm@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        perex@...ex.cz, quic_plai@...cinc.com, quic_rohkumar@...cinc.com,
        robh+dt@...nel.org, srinivas.kandagatla@...aro.org, tiwai@...e.com,
        Venkata Prasad Potturu <quic_potturu@...cinc.com>
Subject: Re: [PATCH v2 1/2] dt-bindings: pinctrl: qcom: sc7280: Add compatible
 string for adsp based platforms

On Fri, Jun 3, 2022 at 8:09 AM Srinivasa Rao Mandadapu
<quic_srivasam@...cinc.com> wrote:
> On 6/2/2022 6:43 AM, Stephen Boyd wrote:

> >> +    enum:
> >> +      - qcom,sc7280-lpass-lpi-pinctrl
> >> +      - qcom,sc7280-lpass-adsp-lpi-pinctrl
> > Can you confirm that this is the same hardware (i.e. same reg property)
> > but just a different compatible string used to convey that the device is
> > using "adsp" mode or not? If so, this looks to be a common pattern for
> > the audio hardware here, where we have two "views" of the hardware, one
> > for adsp mode and one for not adsp mode. I guess the not adsp mode is
> > called "adsp bypass"?
>
> Yes Your understanding is correct. The same hardware in scenario not using ADSP,
>
> and in another enabling DSP.
> >
> > Is that right? Why are we conveying this information via the compatible
> > string?
>
> Could you please suggest better way!.  As pin control driver is the
> first one to probe, I am not getting better approach.
>
> While up-streaming these drivers, concluded to use this approach.

The device tree conveys hardware description and some configuration.

If this is configuration thing, either you could perhaps determine it from the
hardware (if set up in hardware or boot loader) and if that is not possible
it should just be a boolean property of the device
node:

{
    compatible = "...";
    qcom.adsp-mode;
}

If you are probing two different drivers depending on the mode, then there is a
problem of course, but it is a Linux problem not a device tree problem.

Yours,
Linus Walleij