linux-kernel - RE: Re: [PATCH v2 1/2] ASoC: dt-bindings: fsl_rpmsg: List DAPM endpoints ignoring system suspend

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Date:   Wed, 27 Sep 2023 03:07:49 +0000
From:   Chancel Liu <chancel.liu@....com>
To:     Mark Brown <broonie@...nel.org>
CC:     "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
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Subject: RE: Re: [PATCH v2 1/2] ASoC: dt-bindings: fsl_rpmsg: List DAPM
 endpoints ignoring system suspend

> > +  fsl,lpa-widgets:
> > +    $ref: /schemas/types.yaml#/definitions/non-unique-string-array
> > +    description: |
> > +      A list of DAPM endpoints which mark paths between these
> endpoints should
> > +      not be disabled when system enters in suspend state. LPA means low
power
> > +      audio case. 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 can be explained as a mechanism 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. LPA
> requires
> > +      some audio paths still enabled when Cortex-A enters into suspend.
> 
> This is a fairly standard DSP playback case as far as I can see so it
> should work with DAPM without needing this obviously use case specific
> stuff peering into the Linux implementation.  Generally this is done by
> tagging endpoint widgets and DAIs as ignore_suspend, DAPM will then
> figure out the rest of the widgets in the path.

Yes, indeed I meant to let driver get DAPM endpoints from the "fsl,lpa-widgets"
property and then set these endpoints as ignore_suspend if the sound card is
running in this use case. Do you think the description for the use case can be
simplified since it's a common use case?

Regards, 
Chancel Liu