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>

3 files changed, 43 insertions, 10 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;
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 3dc029e106a2..c4840ff75d00 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -316,6 +316,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
         unsigned long jdelta;
         unsigned long curr_jiffies;
         struct timespec curr_tstamp;
+        struct timespec audio_tstamp;
         int crossed_boundary = 0;
 
         old_hw_ptr = runtime->status->hw_ptr;
@@ -328,9 +329,14 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
          */
         pos = substream->ops->pointer(substream);
         curr_jiffies = jiffies;
-        if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE)
+        if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) {
                 snd_pcm_gettime(runtime, (struct timespec *)&curr_tstamp);
 
+                if ((runtime->hw.info & SNDRV_PCM_INFO_HAS_WALL_CLOCK) &&
+                        (substream->ops->wall_clock))
+                        substream->ops->wall_clock(substream, &audio_tstamp);
+        }
+
         if (pos == SNDRV_PCM_POS_XRUN) {
                 xrun(substream);
                 return -EPIPE;
@@ -520,9 +526,31 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
                 snd_BUG_ON(crossed_boundary != 1);
                 runtime->hw_ptr_wrap += runtime->boundary;
         }
-        if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE)
+        if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) {
                 runtime->status->tstamp = curr_tstamp;
 
+                if (!(runtime->hw.info & SNDRV_PCM_INFO_HAS_WALL_CLOCK)) {
+                        /*
+                         * no wall clock available, provide audio timestamp
+                         * derived from pointer position+delay
+                         */
+                        u64 audio_frames, audio_nsecs;
+
+                        if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+                                audio_frames = runtime->hw_ptr_wrap
+                                        + runtime->status->hw_ptr
+                                        - runtime->delay;
+                        else
+                                audio_frames = runtime->hw_ptr_wrap
+                                        + runtime->status->hw_ptr
+                                        + runtime->delay;
+                        audio_nsecs = div_u64(audio_frames * 1000000000LL,
+                                        runtime->rate);
+                        audio_tstamp = ns_to_timespec(audio_nsecs);
+                }
+                runtime->status->audio_tstamp = audio_tstamp;
+        }
+
         return snd_pcm_update_state(substream, runtime);
 }
 
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 5e12e5bacbba..7c800012fff9 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -594,6 +594,8 @@ int snd_pcm_status(struct snd_pcm_substream *substream,
                 snd_pcm_update_hw_ptr(substream);
                 if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) {
                         status->tstamp = runtime->status->tstamp;
+                        status->audio_tstamp =
+                                runtime->status->audio_tstamp;
                         goto _tstamp_end;
                 }
         }