[alsa-devel] [PATCH v2] ALSA: hda - Apply codec delay to wallclock.

[Dylan Reid]

For playback add the codec-side delay to the timestamp, for capture
subtract it.  This brings the timestamps in line with the time that
was recently added to the delay reporting.

Signed-off-by: Dylan Reid <dgreid at chromium.org>
---
Changes since v1:
Calculate nsec from frames, subtract delay for playback as well as
capture.

 sound/pci/hda/hda_intel.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index 735567e..3e6f2c6 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -1889,6 +1889,23 @@ static void azx_timecounter_init(struct snd_pcm_substream *substream,
 		tc->cycle_last = last;
 }
 
+static u64 azx_subtract_codec_delay(struct snd_pcm_substream *substream,
+				u64 nsec)
+{
+	struct azx_pcm *apcm = snd_pcm_substream_chip(substream);
+	struct hda_pcm_stream *hinfo = apcm->hinfo[substream->stream];
+	u64 codec_frames, codec_nsecs;
+
+	if (!hinfo->ops.get_delay)
+		return nsec;
+
+	codec_frames = hinfo->ops.get_delay(hinfo, apcm->codec, substream);
+	codec_nsecs = div_u64(codec_frames * 1000000000LL,
+			      substream->runtime->rate);
+
+	return (nsec > codec_nsecs) ? nsec - codec_nsecs : 0;
+}
+
 static int azx_get_wallclock_tstamp(struct snd_pcm_substream *substream,
 				struct timespec *ts)
 {
@@ -1897,6 +1914,7 @@ static int azx_get_wallclock_tstamp(struct snd_pcm_substream *substream,
 
 	nsec = timecounter_read(&azx_dev->azx_tc);
 	nsec = div_u64(nsec, 3); /* can be optimized */
+	nsec = azx_subtract_codec_delay(substream, nsec);
 
 	*ts = ns_to_timespec(nsec);
 
-- 
1.8.1.3.605.g02339dd