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

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Date: Tue, 19 Mar 2024 10:26:08 +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

> We can discuss that offline and come up with an approach that is
> reviewable by maintainers and the community.

Sure, looking forward to working together with you!

Thanks,
Albert Wang

On Fri, Mar 15, 2024 at 4:57 AM Wesley Cheng <quic_wcheng@...cinc.com> wrote:
>
> Hi Albert
>
> On 3/14/2024 3:29 AM, Albert Wang wrote:
> > 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?
> >
>
> Correct, this series does not cover this mechanism.
>
> >> 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.
> >
>
> We can discuss that offline and come up with an approach that is
> reviewable by maintainers and the community.
>
> Thanks
> Wesley Cheng
>
> > 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