ALSA: core: group read of pointer, tstamp and jiffies

Group read of hw_ptr, tstamp and jiffies in a sequence
for better correlation. Previous code took timestamp at the
end, which could introduce delays between audio time and
system time.

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

1 files changed, 18 insertions, 5 deletions

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index faedb1481b24..8f312fa6c282 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -313,9 +313,22 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
         snd_pcm_uframes_t old_hw_ptr, new_hw_ptr, hw_base;
         snd_pcm_sframes_t hdelta, delta;
         unsigned long jdelta;
+        unsigned long curr_jiffies;
+        struct timespec curr_tstamp;
 
         old_hw_ptr = runtime->status->hw_ptr;
+
+        /*
+         * group pointer, time and jiffies reads to allow for more
+         * accurate correlations/corrections.
+         * The values are stored at the end of this routine after
+         * corrections for hw_ptr position
+         */
         pos = substream->ops->pointer(substream);
+        curr_jiffies = jiffies;
+        if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE)
+                snd_pcm_gettime(runtime, (struct timespec *)&curr_tstamp);
+
         if (pos == SNDRV_PCM_POS_XRUN) {
                 xrun(substream);
                 return -EPIPE;
@@ -343,7 +356,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
                 delta = runtime->hw_ptr_interrupt + runtime->period_size;
                 if (delta > new_hw_ptr) {
                         /* check for double acknowledged interrupts */
-                        hdelta = jiffies - runtime->hw_ptr_jiffies;
+                        hdelta = curr_jiffies - runtime->hw_ptr_jiffies;
                         if (hdelta > runtime->hw_ptr_buffer_jiffies/2) {
                                 hw_base += runtime->buffer_size;
                                 if (hw_base >= runtime->boundary)
@@ -388,7 +401,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
                  * Without regular period interrupts, we have to check
                  * the elapsed time to detect xruns.
                  */
-                jdelta = jiffies - runtime->hw_ptr_jiffies;
+                jdelta = curr_jiffies - runtime->hw_ptr_jiffies;
                 if (jdelta < runtime->hw_ptr_buffer_jiffies / 2)
                         goto no_delta_check;
                 hdelta = jdelta - delta * HZ / runtime->rate;
@@ -430,7 +443,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
         if (hdelta < runtime->delay)
                 goto no_jiffies_check;
         hdelta -= runtime->delay;
-        jdelta = jiffies - runtime->hw_ptr_jiffies;
+        jdelta = curr_jiffies - runtime->hw_ptr_jiffies;
         if (((hdelta * HZ) / runtime->rate) > jdelta + HZ/100) {
                 delta = jdelta /
                         (((runtime->period_size * HZ) / runtime->rate)
@@ -492,9 +505,9 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
         }
         runtime->hw_ptr_base = hw_base;
         runtime->status->hw_ptr = new_hw_ptr;
-        runtime->hw_ptr_jiffies = jiffies;
+        runtime->hw_ptr_jiffies = curr_jiffies;
         if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE)
-                snd_pcm_gettime(runtime, (struct timespec *)&runtime->status->tstamp);
+                runtime->status->tstamp = curr_tstamp;
 
         return snd_pcm_update_state(substream, runtime);
 }