Re: [PATCH 2/2] ALSA: pcm: auto-fill buffer with silence when draining playback

[Takashi Iwai <tiwai@suse.de>]

On Sat, 08 Apr 2023 01:58:21 +0200,
Jaroslav Kysela wrote:
> 
> On 05. 04. 23 22:12, Oswald Buddenhagen wrote:
> > Draining will always playback somewhat beyond the end of the filled
> > buffer. This would produce artifacts if the user did not set up the
> > auto-silencing machinery. This patch makes it work out of the box.
> > 
> > Rather than figuring out the right threshold (which is one period plus
> > the card-specific FIFO size plus some IRQ jitter), we use "top-up" mode.
> > 
> > Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
> 
> I think that it was really bad decision to apply this patch without a
> broader discussion. When we designed the API, we knew about described
> problems and we decided to keep this up to applications. The silencing
> may not help in all cases where the PCM samples ends with a high
> volume. A volume ramping should be used and it's an application
> job. Also, silencing touches the DMA buffer which may not be
> desired. And lastly drivers can handle draining correctly (stop at the
> exact position - see substream->ops->trigger with
> SNDRV_PCM_TRIGGER_DRAIN argument).
> 
> I would create a new API extension for this (new ioctl or sw_params
> flag), but the default behaviour should be retained.
> 
> I will try to review the first patch too, but my time is limited over Easter.

OK, thanks.  I'll drop the patch meanwhile.

Applying the silencing blindly might be an overkill, indeed, although
this could be seen as an easy solution.  Let's see.


Takashi