linux-kernel - Re: [PATCH v9 0/5] Support system sleep with offloaded usb transfers

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Message-ID: <CAOuDEK2u509kNjyL6qm27QgvtoCscRcsLixW=W8ABz2NF8A-tw@mail.gmail.com>
Date: Mon, 3 Feb 2025 10:57:00 +0800
From: Guan-Yu Lin <guanyulin@...gle.com>
To: Pierre-Louis Bossart <pierre-louis.bossart@...ux.dev>
Cc: gregkh@...uxfoundation.org, Thinh.Nguyen@...opsys.com, 
	mathias.nyman@...el.com, stern@...land.harvard.edu, perex@...ex.cz, 
	tiwai@...e.com, sumit.garg@...aro.org, kekrby@...il.com, oneukum@...e.com, 
	ricardo@...liere.net, lijiayi@...inos.cn, quic_jjohnson@...cinc.com, 
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-sound@...r.kernel.org
Subject: Re: [PATCH v9 0/5] Support system sleep with offloaded usb transfers

On Tue, Jan 28, 2025 at 11:22 PM Pierre-Louis Bossart
<pierre-louis.bossart@...ux.dev> wrote:
>
> I am not following, sorry.
>
> Is the desired outcome to
>
> a) prevent the system from entering S3 if there is an active USB audio offloaded stream?
>
> or b) allow offloaded transactions even when the system is in S3?
>
>
> which is it?
>
> a) would be rather interesting, but currently we don't have any such behavior supported. When the system enters S3 all audio stops. The stream will resume when the system goes back to S0. Do we really want the battery to drain in S3?
>
> b) seems rather complicated, once the on-going DMA transfers complete then who's going to refill buffers for the USB offloaded streams? Allowing the lowest level to operate even in S3 is only a small part of the puzzle, someone's got to provide data at some point. Unless the data is generated also by a side DSP having access to mass storage or wireless interfaces?

Thanks for the question, the intent of our proposal should be (b), to
allow offloaded transactions even when the system is in S3.
In our design, the DSP wakes the system before the buffers are fully
drained. This patchset enables the USB controller for offloaded
transfers during system suspend (S3). To be precise, this patchset
focuses solely on enabling the USB controller in S3 and does not
include other necessary components for continuous offloaded USB
transfers. I'll revise the commit message/cover letter to reflect
this.Thanks for highlighting the potential ambiguity.

Regards,
Guan-Yu