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>
diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
index 91cdf94..af2a3fd 100644
--- a/sound/core/pcm_compat.c
+++ b/sound/core/pcm_compat.c
@@ -190,7 +190,8 @@
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 @@
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 @@
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 @@
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;