At Sun, 22 Feb 2009 00:45:04 +0100, Lennart Poettering wrote:

On Tue, 07.10.08 17:32, Takashi Iwai (tiwai@suse.de) wrote:

...

Hi,

Sorry for the overly long delay.

...

the patch below (to the latest sound git tree) adds the extra delay count for USB-audio driver. This change will appear as the return value of snd_pcm_delay().

Could you check whether it's appropriate behavior you've wanted?

I have now tested this patch on the current 2.6.29-rc5 kernel. The effect is that snd_pcm_delay() returns always increasing values, as if the playback never proceeds. Most movie players which need that call to synchronize video frames hence stall completely.

OK, that's bad. However, the increased value of snd_pcm_delay() is exactly the effect. The usb-audio always prefetch the buffer in advance.

That means, changing (or "fixing") snd_pcm_delay() would cause many regressions with many apps -- thus basically we are not allowed to change the semantics any more at this too late point.

I feel it's better to introduce another kernel-side API to give a better sync/timing information, and mark snd_pcm_delay as obsolete for future (although we can never deprecate such a basic API).

Takashi

Lennart

...

diff --git a/include/sound/pcm.h b/include/sound/pcm.h index 40c5a6f..dcbdc60 100644 --- a/include/sound/pcm.h +++ b/include/sound/pcm.h @@ -269,6 +269,7 @@ struct snd_pcm_runtime { snd_pcm_uframes_t avail_max; snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */ snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/

• snd_pcm_sframes_t delay; /* extra delay; typically FIFO size */

  /* -- HW params -- */ snd_pcm_access_t access; /* access mode */

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index e61e125..df7c3fa 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -597,14 +597,15 @@ int snd_pcm_status(struct snd_pcm_substream *substream, if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) { status->avail = snd_pcm_playback_avail(runtime); if (runtime->status->state == SNDRV_PCM_STATE_RUNNING ||

•     runtime->status->state == SNDRV_PCM_STATE_DRAINING)
  

•     runtime->status->state == SNDRV_PCM_STATE_DRAINING) {
  status->delay = runtime->buffer_size - status->avail;
  

• else
  

• 	status->delay += runtime->delay;
  

• } else
  status->delay = 0;
  

  } else { status->avail = snd_pcm_capture_avail(runtime); if (runtime->status->state == SNDRV_PCM_STATE_RUNNING)

• 	status->delay = status->avail;
  

• 	status->delay = status->avail + runtime->delay;
  

  else status->delay = 0; }

@@ -2423,6 +2424,7 @@ static int snd_pcm_delay(struct snd_pcm_substream *substream, n = snd_pcm_playback_hw_avail(runtime); else n = snd_pcm_capture_avail(runtime);

• n += runtime->delay;
  

  break; case SNDRV_PCM_STATE_XRUN: err = -EPIPE;

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c index 6e70ba4..7d5a103 100644 --- a/sound/usb/usbaudio.c +++ b/sound/usb/usbaudio.c @@ -629,6 +629,7 @@ static int prepare_playback_urb(struct snd_usb_substream *subs, subs->hwptr_done += offs; if (subs->hwptr_done >= runtime->buffer_size) subs->hwptr_done -= runtime->buffer_size;

• runtime->delay += offs; spin_unlock_irqrestore(&subs->lock, flags); urb->transfer_buffer_length = offs * stride; if (period_elapsed)

@@ -638,12 +639,20 @@ static int prepare_playback_urb(struct snd_usb_substream *subs,

/*

• process after playback data complete

• • • nothing to do

• • • decrease the delay count again
  */

static int retire_playback_urb(struct snd_usb_substream *subs, struct snd_pcm_runtime *runtime, struct urb *urb) {

• unsigned long flags;
• int stride = runtime->frame_bits >> 3;
• int processed = urb->transfer_buffer_length / stride;
• spin_lock_irqsave(&subs->lock, flags);
• if (processed > runtime->delay)

• runtime->delay -= processed;
  

• spin_unlock_irqrestore(&subs->lock, flags); return 0;

}

@@ -1542,6 +1551,7 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream) subs->hwptr_done = 0; subs->transfer_done = 0; subs->phase = 0;

• runtime->delay = 0;

  /* clear urbs (to be sure) */ deactivate_urbs(subs, 0, 1);

---

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Lennart

-- Lennart Poettering Red Hat, Inc. lennart [at] poettering [dot] net ICQ# 11060553 http://0pointer.net/lennart/ GnuPG 0x1A015CC4