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

[Chancel Liu]

> > 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@xxxxxxx>
> > ---
> >  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