linux-kernel - Re: [PATCH v18 20/41] ALSA: usb-audio: qcom: Introduce QC USB SND offloading support

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Date: Thu, 14 Mar 2024 18:29:47 +0800
From: Albert Wang <albertccwang@...gle.com>
To: Wesley Cheng <quic_wcheng@...cinc.com>
Cc: srinivas.kandagatla@...aro.org, mathias.nyman@...el.com, perex@...ex.cz, 
	conor+dt@...nel.org, corbet@....net, lgirdwood@...il.com, 
	andersson@...nel.org, krzysztof.kozlowski+dt@...aro.org, 
	gregkh@...uxfoundation.org, Thinh.Nguyen@...opsys.com, broonie@...nel.org, 
	bgoswami@...cinc.com, tiwai@...e.com, robh+dt@...nel.org, 
	konrad.dybcio@...aro.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-sound@...r.kernel.org, 
	linux-usb@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-doc@...r.kernel.org, alsa-devel@...a-project.org
Subject: Re: [PATCH v18 20/41] ALSA: usb-audio: qcom: Introduce QC USB SND
 offloading support

On Thu, Mar 14, 2024 at 3:18 AM Wesley Cheng <quic_wcheng@...cinc.com> wrote:
>
> Hi Albert,
>
> On 3/13/2024 1:03 AM, Albert Wang wrote:
> > Hi Wesley,
> >
> > The suspend function `qc_usb_audio_offload_suspend()` looks to stop
> > the traffic on the bus, so that the bus can be suspended. That allows
> > the application processor(AP) to enter suspend. There is a subtle
> > difference with our feature, which is to allow AP suspend with the
> > Host and USB controller active to continue the audio offloading. We
> > call this feature `allow AP suspend in playback`. So, I have some
> > points to clarify with you:
>
> Yes, I'm aware of that feature also.
>
> > 1. Will the suspend flow `usb_audio_suspend() -->
> > platform_ops->suspend_cb() --> qc_usb_audio_offload_suspend()` be
> > called when offloading is active?
>
> It can be.  This is why in our case, we are going to issue the
> disconnect event to the audio DSP to stop the session if it is currently
> in one.
>
> > 2. As my understanding, the suspend function is to allow AP suspend
> > when the offloading is IDLE, but it won't allow AP suspend when in
> > playback or capture. Please correct me if anything is wrong.
>
> As mentioned above, it will let apps go into PM suspend after forcing
> the audio stream to be idle.  We won't block PM suspend entry.
>
Right. Your design is to force the audio stream idle, or say, inform
the audio DSP
to stop the current offloading session first, then AP can go into PM
suspend as usual.
Then I can say the current design did not support the `allow AP
suspend in playback`
feature, right?

> Yes, I saw that patch as well.  I'll take a look once this series lands
> upstream.

That patch is rejected and archived now. So we need to find another
approach to do
that, even based on your framework.

Thanks,
Albert


> > 3. We would like to integrate the `allow AP suspend in playback`
> > feature with your framework to become one upstream offload solution.
> > Here is the patch:
> > https://patchwork.kernel.org/project/linux-pm/patch/20240223143833.1509961-1-guanyulin@google.com/
> > .
>
> Yes, I saw that patch as well.  I'll take a look once this series lands
> upstream.
>
> Thanks
> Wesley Cheng