[alsa-devel] [PATCH 1/4] ALSA: x86: Don't pass SNDRV_PCM_INFO_BATCH flag

[Takashi Iwai]

On Fri, 03 Feb 2017 20:39:49 +0100,
Pierre-Louis Bossart wrote:
> 
> On 2/3/17 10:43 AM, Takashi Iwai wrote:
> > The PCM engine on LPE audio isn't like a batch-style process, but
> > rather it deals with the standard ring buffer.  Passing the BATCH info
> > flag is inappropriate.
> 
> Humm, this is controversial. There are 4 DMA descriptors and getting a
> precise position in the stream is not straightforward.

Well, as far as I've tested, it is.  The buffer length register keeps
the remaining bytes, and you can easily read out and compute the
current position in fairly exact manner.  Even the old driver has that
information -- the patch David added does it.

> Rewind is also
> not supported so if you remove the BATCH flag you will push PulseAudio
> into doing timer-based scheduling and rewinds that probably don't
> work.

I don't think there is much difference regarding this.
Please check the buffer manage description in my previous post.

In anyway, it'd be appreciated if you can test on your hardware.
I could test only on a single machine.


thanks,

Takashi


> >
> > Similarly, the DOUBLE flag is also superfluous.  Drop both bits.
> >
> > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> > ---
> >  sound/x86/intel_hdmi_audio.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/sound/x86/intel_hdmi_audio.c b/sound/x86/intel_hdmi_audio.c
> > index c83f02c2593e..32a21422e6f5 100644
> > --- a/sound/x86/intel_hdmi_audio.c
> > +++ b/sound/x86/intel_hdmi_audio.c
> > @@ -131,10 +131,8 @@ static const struct channel_map_table map_tables[] = {
> >  /* hardware capability structure */
> >  static const struct snd_pcm_hardware snd_intel_hadstream = {
> >  	.info =	(SNDRV_PCM_INFO_INTERLEAVED |
> > -		SNDRV_PCM_INFO_DOUBLE |
> >  		SNDRV_PCM_INFO_MMAP|
> > -		SNDRV_PCM_INFO_MMAP_VALID |
> > -		SNDRV_PCM_INFO_BATCH),
> > +		SNDRV_PCM_INFO_MMAP_VALID),
> >  	.formats = (SNDRV_PCM_FMTBIT_S24 |
> >  		SNDRV_PCM_FMTBIT_U24),
> >  	.rates = SNDRV_PCM_RATE_32000 |
> >
>