ALSA: core: add hooks for audio timestamps

ALSA did not provide any direct means to infer the audio time for A/V
sync and system/audio time correlations (eg. PulseAudio).
Applications had to track the number of samples read/written and
add/subtract the number of samples queued in the ring buffer.  This
accounting led to small errors, typically several samples, due to the
two-step process.  Computing the audio time in the kernel is more
direct, as all the information is available in the same routines.

Also add new .audio_wallclock routine to enable fine-grain synchronization
between monotonic system time and audio hardware time.
Using the wallclock, if supported in hardware, allows for a
much better sub-microsecond precision and a common drift tracking for
all devices sharing the same wall clock (master clock).

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

1 files changed, 11 insertions, 8 deletions

diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index 91cdf9435fec..af2a3fdb8828 100644
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -190,7 +190,8 @@ struct snd_pcm_status32 {
 	u32 avail_max;
 	u32 overrange;
 	s32 suspended_state;
-	unsigned char reserved[60];
+	struct compat_timespec audio_tstamp;
+	unsigned char reserved[60-sizeof(struct compat_timespec)];
 } __attribute__((packed));
 
 
@@ -205,17 +206,16 @@ static int snd_pcm_status_user_compat(struct snd_pcm_substream *substream,
 		return err;
 
 	if (put_user(status.state, &src->state) ||
-	    put_user(status.trigger_tstamp.tv_sec, &src->trigger_tstamp.tv_sec) ||
-	    put_user(status.trigger_tstamp.tv_nsec, &src->trigger_tstamp.tv_nsec) ||
-	    put_user(status.tstamp.tv_sec, &src->tstamp.tv_sec) ||
-	    put_user(status.tstamp.tv_nsec, &src->tstamp.tv_nsec) ||
+	    compat_put_timespec(&status.trigger_tstamp, &src->trigger_tstamp) ||
+	    compat_put_timespec(&status.tstamp, &src->tstamp) ||
 	    put_user(status.appl_ptr, &src->appl_ptr) ||
 	    put_user(status.hw_ptr, &src->hw_ptr) ||
 	    put_user(status.delay, &src->delay) ||
 	    put_user(status.avail, &src->avail) ||
 	    put_user(status.avail_max, &src->avail_max) ||
 	    put_user(status.overrange, &src->overrange) ||
-	    put_user(status.suspended_state, &src->suspended_state))
+	    put_user(status.suspended_state, &src->suspended_state) ||
+	    compat_put_timespec(&status.audio_tstamp, &src->audio_tstamp))
 		return -EFAULT;
 
 	return err;
@@ -364,6 +364,7 @@ struct snd_pcm_mmap_status32 {
 	u32 hw_ptr;
 	struct compat_timespec tstamp;
 	s32 suspended_state;
+	struct compat_timespec audio_tstamp;
 } __attribute__((packed));
 
 struct snd_pcm_mmap_control32 {
@@ -426,12 +427,14 @@ static int snd_pcm_ioctl_sync_ptr_compat(struct snd_pcm_substream *substream,
 	sstatus.hw_ptr = status->hw_ptr % boundary;
 	sstatus.tstamp = status->tstamp;
 	sstatus.suspended_state = status->suspended_state;
+	sstatus.audio_tstamp = status->audio_tstamp;
 	snd_pcm_stream_unlock_irq(substream);
 	if (put_user(sstatus.state, &src->s.status.state) ||
 	    put_user(sstatus.hw_ptr, &src->s.status.hw_ptr) ||
-	    put_user(sstatus.tstamp.tv_sec, &src->s.status.tstamp.tv_sec) ||
-	    put_user(sstatus.tstamp.tv_nsec, &src->s.status.tstamp.tv_nsec) ||
+	    compat_put_timespec(&sstatus.tstamp, &src->s.status.tstamp) ||
 	    put_user(sstatus.suspended_state, &src->s.status.suspended_state) ||
+	    compat_put_timespec(&sstatus.audio_tstamp,
+		    &src->s.status.audio_tstamp) ||
 	    put_user(scontrol.appl_ptr, &src->c.control.appl_ptr) ||
 	    put_user(scontrol.avail_min, &src->c.control.avail_min))
 		return -EFAULT;