linux-kernel - Re: [Patch v2] ALSA: compress: allow to leave draining state when pausing in draining

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Date:   Fri, 9 Jul 2021 10:08:29 +0800
From:   Robert Lee <lerobert@...gle.com>
To:     Jaroslav Kysela <perex@...ex.cz>
Cc:     Takashi Iwai <tiwai@...e.de>, vkoul@...nel.org, tiwai@...e.com,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        carterhsu@...gle.com, zxinhui@...gle.com, bubblefang@...gle.com
Subject: Re: [Patch v2] ALSA: compress: allow to leave draining state when
 pausing in draining

Jaroslav Kysela <perex@...ex.cz> 於 2021年7月8日 週四 下午10:53寫道：
>
> On 08. 07. 21 15:47, Robert Lee wrote:
> > Hi Takashi,
> >
> > It is a little complex to describe the design in detail, but try to
> > explain simply
> > what issue we meet.
> >
> > If w/o the change,  after user resumes from the pause, our system would call
> > snd_compr_drain() or snd_compr_partial_drain() again after it returns from
> > previous drain (when EOF reaches). Then it will block in this drain and no one
> > wake it up because EOF has already reached. I add this change to return from
> > the previous drain.
>
> It looks like that the driver does not call snd_compr_drain_notify() so the
> state is not updated to SETUP on EOF.
>
We indeed call snd_compr_drain_notify() on EOF, but after return from
wait_for _drain there is another drain again immediately.
Looks like the system queue some states change on user space and need
to drain again after resume from pause.
I suppose there is different design on user space so I add the hook to
handle diffent usage.

> > Actually, I am wondering how the pause-during-drain can keep the state in
> > DRAINING. It should have a different design. :)
>
> I already proposed to add a new state (because it's a new state), but the
> conservative way was elected to avoid user space changes.
>
>                                 Jaroslav
>
> --
> Jaroslav Kysela <perex@...ex.cz>
> Linux Sound Maintainer; ALSA Project; Red Hat, Inc.