linux-kernel - RE: Re: [PATCH 1/2] ASoC: dt-bindings: fsl_rpmsg: List DAPM endpoints ignoring suspend

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Date:   Mon, 25 Sep 2023 08:20:22 +0000
From:   Chancel Liu <chancel.liu@....com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "conor+dt@...nel.org" <conor+dt@...nel.org>,
        "shengjiu.wang@...il.com" <shengjiu.wang@...il.com>,
        "Xiubo.Lee@...il.com" <Xiubo.Lee@...il.com>,
        "festevam@...il.com" <festevam@...il.com>,
        "nicoleotsuka@...il.com" <nicoleotsuka@...il.com>,
        "perex@...ex.cz" <perex@...ex.cz>,
        "tiwai@...e.com" <tiwai@...e.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: Re: [PATCH 1/2] ASoC: dt-bindings: fsl_rpmsg: List DAPM endpoints
 ignoring suspend

> > Add a property to list DAPM endpoints which mark paths between these
> > endpoints ignoring suspend. These DAPM paths can still be power on
> > when system enters into suspend.
> >
> > Signed-off-by: Chancel Liu <chancel.liu@....com>
> > ---
> >  Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml
> > b/Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml
> > index 188f38baddec..ec6e09eab427 100644
> > --- a/Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml
> > +++ b/Documentation/devicetree/bindings/sound/fsl,rpmsg.yaml
> > @@ -91,6 +91,12 @@ properties:
> >        - rpmsg-audio-channel
> >        - rpmsg-micfil-channel
> >
> > +  fsl,lpa-widgets:
> 
> What is LPA? It's not explained in property description.
> 

On asymmetric multiprocessor, there are Cortex-A core and Cortex-M core, Linux
is running on Cortex-A core, RTOS or other OS is running on Cortex-M core. The
audio hardware devices can be controlled by Cortex-M. LPA means low power audio
case. The mechanism can be explained that Cortex-A allocates a large buffer and
fill audio data, then Cortex-A can enter into suspend for the purpose of power
saving. Cortex-M continues to play the sound during suspend phase of Cortex-A.
When the data in buffer is consumed, Cortex-M will trigger the Cortex-A to
wakeup to fill data.

I can add above explanation to LPA in patch v2.

> > +    $ref: /schemas/types.yaml#/definitions/non-unique-string-array
> > +    description: |
> > +      A list of DAPM endpoints which mark paths between these endpoints
> > +      ignoring suspend.
> 
> And how does it differ from audio-routing? Also, you need to explain what is
> "suspend" in this context. Bindings are independent of Linux.
> 

Normally audio paths will be disabled by ASoC dynamic audio power management if
Linux enters into suspend. LPA requires some audio paths enabled when Cortex-A
enters into suspend. We can read DAPM endpoints from the "fsl,lpa-widgets"
property and keep the paths between these endpoints enabled during suspend
phase of Cortex-A. Property "audio-routing" just declares the connection
between widgets and doesn't have such feature.

I will modify the description as following:
"A list of DAPM endpoints which mark paths between these endpoints still enabled
when system enters into suspend."

> Best regards,
> Krzysztof

Regards, 
Chancel Liu