Date:   Thu, 8 Jul 2021 21:47:24 +0800
From:   Robert Lee <lerobert@...gle.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     vkoul@...nel.org, perex@...ex.cz, 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

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.

And yes, after user resumes it, it will change state to RUNNING. Then it will
call snd_compr_drain() or snd_compr_partial_drain() very soon and change
state to DRAINING again.

Actually, I am wondering how the pause-during-drain can keep the state in
DRAINING. It should have a different design. :)

I also checked the snd_compr_open() comment, and it doesn't mention that
we cannot pause in DRAINING state. Looks like it needs to be updated according
to these changes. Maybe it can be updated in another commit?

* SNDRV_PCM_STATE_DRAINING: When stream is draining current data. This is done
 *      by calling SNDRV_COMPRESS_DRAIN.
 * SNDRV_PCM_STATE_PAUSED: When stream is paused. This is done by calling
 *      SNDRV_COMPRESS_PAUSE. It can be stopped or resumed by calling
 *      SNDRV_COMPRESS_STOP or SNDRV_COMPRESS_RESUME respectively.

thanks,
Robert.

Takashi Iwai <tiwai@...e.de> 於 2021年7月8日 週四 下午7:24寫道：


Takashi Iwai <tiwai@...e.de> 於 2021年7月8日 週四 下午7:24寫道：
>
> On Thu, 08 Jul 2021 04:08:15 +0200,
> Robert Lee wrote:
> >
> > When compress offload pauses in draining state, not all platforms
> > need to keep in draining state. Some platforms may call drain or
> > partial drain again when resume from pause in draining, so it needs
> > to wake up from snd_compress_wait_for_drain() in this case.
> >
> > Call API snd_compr_leave_draining_in_pause(), if the platform
> > doesn't need to keep in draining state when pause in draining
> > state.
> >
> > Signed-off-by: Robert Lee <lerobert@...gle.com>
> > ---
> >  include/sound/compress_driver.h | 14 ++++++++++++++
> >  sound/core/compress_offload.c   |  8 +++++++-
> >  2 files changed, 21 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/sound/compress_driver.h b/include/sound/compress_driver.h
> > index 277087f635f3..e16524a93a14 100644
> > --- a/include/sound/compress_driver.h
> > +++ b/include/sound/compress_driver.h
> > @@ -145,6 +145,7 @@ struct snd_compr_ops {
> >   * @lock: device lock
> >   * @device: device id
> >   * @use_pause_in_draining: allow pause in draining, true when set
> > + * @leave_draining_in_pause: leave draining state when pausing in draining
> >   */
> >  struct snd_compr {
> >       const char *name;
> > @@ -156,6 +157,7 @@ struct snd_compr {
> >       struct mutex lock;
> >       int device;
> >       bool use_pause_in_draining;
> > +     bool leave_draining_in_pause;
> >  #ifdef CONFIG_SND_VERBOSE_PROCFS
> >       /* private: */
> >       char id[64];
> > @@ -182,6 +184,18 @@ static inline void snd_compr_use_pause_in_draining(struct snd_compr_stream *subs
> >       substream->device->use_pause_in_draining = true;
> >  }
> >
> > +/**
> > + * snd_compr_leave_draining_in_pause - Leave draining state when pause in draining
> > + * @substream: compress substream to set
> > + *
> > + * In some platform, we need to leave draining state when we use pause in draining.
> > + * Add API to allow leave draining state.
> > + */
> > +static inline void snd_compr_leave_draining_in_pause(struct snd_compr_stream *substream)
> > +{
> > +     substream->device->leave_draining_in_pause = true;
> > +}
> > +
> >  /* dsp driver callback apis
> >   * For playback: driver should call snd_compress_fragment_elapsed() to let the
> >   * framework know that a fragment has been consumed from the ring buffer
> > diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> > index 21ce4c056a92..c6e5c8f072d7 100644
> > --- a/sound/core/compress_offload.c
> > +++ b/sound/core/compress_offload.c
> > @@ -719,8 +719,14 @@ static int snd_compr_pause(struct snd_compr_stream *stream)
> >               if (!stream->device->use_pause_in_draining)
> >                       return -EPERM;
> >               retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_PUSH);
> > -             if (!retval)
> > +             if (!retval) {
> > +                     if (stream->device->leave_draining_in_pause) {
> > +                             stream->runtime->state = SNDRV_PCM_STATE_PAUSED;
> > +                             wake_up(&stream->runtime->sleep);
> > +                             break;
> > +                     }
> >                       stream->pause_in_draining = true;
> > +             }
>
> Hrm, what actually happens with this new flag?  It changes the state
> to PAUSED even if it's done during the draining.  Then user resumes
> the pause via snd_compr_resume(), and now the state changes to
> RUNNING.  OTOH, if the draining runs normally, it'll end up with
> SETUP.
>
> Even if the above is even designed behavior, it must be described
> properly somewhere.  The state change is described in snd_compr_open()
> comment, and the new behavior should be mentioned there as well.
> (Admittedly, the previous hack for the pause-during-drain is also
> missing and should have been mentioned there; but an excuse is that
> the pause-during-drain doesn't change the state itself :)
>
>
> thanks,
>
> Takashi

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