ALSA: pcm: allow for trigger_tstamp snapshot in .trigger

Don't use generic snapshot of trigger_tstamp if low-level driver or
hardware can get a more precise value for better audio/system time
synchronization.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 4 insertions, 1 deletions

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 07299b295233..c0ddb7e69c28 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -285,6 +285,7 @@ struct snd_pcm_runtime {
         /* -- Status -- */
         struct snd_pcm_substream *trigger_master;
         struct timespec trigger_tstamp; /* trigger timestamp */
+        bool trigger_tstamp_latched;     /* trigger timestamp latched in low-level driver/hardware */
         int overrange;
         snd_pcm_uframes_t avail_max;
         snd_pcm_uframes_t hw_ptr_base;  /* Position at buffer restart */
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 4ecd35fbfe3f..b03a638b420c 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -810,7 +810,8 @@ static void snd_pcm_trigger_tstamp(struct snd_pcm_substream *substream)
         if (runtime->trigger_master == NULL)
                 return;
         if (runtime->trigger_master == substream) {
-                snd_pcm_gettime(runtime, &runtime->trigger_tstamp);
+                if (!runtime->trigger_tstamp_latched)
+                        snd_pcm_gettime(runtime, &runtime->trigger_tstamp);
         } else {
                 snd_pcm_trigger_tstamp(runtime->trigger_master);
                 runtime->trigger_tstamp = runtime->trigger_master->runtime->trigger_tstamp;
@@ -979,6 +980,7 @@ static int snd_pcm_pre_start(struct snd_pcm_substream *substream, int state)
         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
             !snd_pcm_playback_data(substream))
                 return -EPIPE;
+        runtime->trigger_tstamp_latched = false;
         runtime->trigger_master = substream;
         return 0;
 }