Re: [PATCH] ALSA: pcm: reinvent the stream synchronization ID API

[Jaroslav Kysela <perex@xxxxxxxx>]

On 06. 05. 24 11:02, Amadeusz Sławiński wrote:
> On 4/30/2024 6:10 PM, Jaroslav Kysela wrote:
> > Until the commit e11f0f90a626 ("ALSA: pcm: remove SNDRV_PCM_IOCTL1_INFO
> > internal command"), there was a possibility to pass information
> > about the synchronized streams to the user space. The mentioned
> > commit removed blindly the appropriate code with an irrelevant comment.
> >
> > The revert may be appropriate, but since this API was lost for several
> > years without any complains, it's time to improve it. The hardware
> > parameters may change the used stream clock source (e.g. USB hardware)
> > so move this synchronization ID to hw_params as read-only field.
> >
> > It seems that pipewire can benefit from this API (disable adaptive
> > resampling for perfectly synchronized PCM streams) now.
> >
> > Cc: Takashi Sakamoto <takaswie@xxxxxxxxxx>
> > Signed-off-by: Jaroslav Kysela <perex@xxxxxxxx>
> > ---
> >    include/sound/pcm.h         |  9 +++++++++
> >    include/uapi/sound/asound.h |  8 +++++---
> >    sound/core/pcm_lib.c        | 13 +++++++++++++
> >    sound/core/pcm_native.c     |  6 ++++++
> >    4 files changed, 33 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/sound/pcm.h b/include/sound/pcm.h
> > index 210096f124ee..f716e0d0d174 100644
> > --- a/include/sound/pcm.h
> > +++ b/include/sound/pcm.h
> > @@ -93,6 +93,7 @@ struct snd_pcm_ops {
> >    #define SNDRV_PCM_IOCTL1_CHANNEL_INFO	2
> >    /* 3 is absent slot. */
> >    #define SNDRV_PCM_IOCTL1_FIFO_SIZE	4
> > +#define SNDRV_PCM_IOCTL1_SYNC_ID	5
> >    
> >    #define SNDRV_PCM_TRIGGER_STOP		0
> >    #define SNDRV_PCM_TRIGGER_START		1
> > @@ -1565,6 +1566,14 @@ static inline u64 pcm_format_to_bits(snd_pcm_format_t pcm_format)
> >    	     (__force int)(f) <= (__force int)SNDRV_PCM_FORMAT_LAST;	\
> >    	     (f) = (__force snd_pcm_format_t)((__force int)(f) + 1))
> >    
> > +/**
> > + * is sync id (clock id) empty?
> > + */
> > +static inline bool pcm_sync_empty(union snd_pcm_sync_id *sync)
> > +{
> > +	return sync->id64[0] == 0 && sync->id64[1] == 0;
>
> Can you use SNDRV_PCM_STREAM_PLAYBACK and SNDRV_PCM_STREAM_CAPTURE here,
> for someone not familiar with ALSA code above will be confusing.

It's not related to stream direction. Anyway, I'll send an updated patch based 
on Takashi's comment soon with some other changes.

				Thanks,
					Jaroslav

--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.