ALSA: pcm midlevel code - add time check for double interrupt acknowledge

The current code in pcm_lib.c do all checks using only the position
in the ring buffer. Unfortunately, where the interrupts gets delayed or
merged into one, we need another timing source to check when the
buffer size boundary overlaps to avoid the wrong updating of the
ring buffer pointers.

This code uses jiffies to check the right time window without any
performance impact.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 85f1c6bf8566944eaa85d6b8742ebef2a06e6ce9..dfd9b76b185306a40fff57df94ad53ab83d2f966 100644 (file)
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -278,6 +278,7 @@ struct snd_pcm_runtime {
        snd_pcm_uframes_t hw_ptr_base;  /* Position at buffer restart */
        snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time */
        unsigned long hw_ptr_jiffies;   /* Time when hw_ptr is updated */
+       unsigned long hw_ptr_buffer_jiffies; /* buffer time in jiffies */
        snd_pcm_sframes_t delay;        /* extra delay; typically FIFO size */
 
        /* -- HW params -- */

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index e23e0e7ab26f9ff5f02204ca62422a14cc674e5e..a1707cca9c6635c8b4cd7e79b5cebe21bffc2d9e 100644 (file)
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -334,11 +334,15 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
                /* delta = "expected next hw_ptr" for in_interrupt != 0 */
                delta = runtime->hw_ptr_interrupt + runtime->period_size;
                if (delta > new_hw_ptr) {
-                       hw_base += runtime->buffer_size;
-                       if (hw_base >= runtime->boundary)
-                               hw_base = 0;
-                       new_hw_ptr = hw_base + pos;
-                       goto __delta;
+                       /* check for double acknowledged interrupts */
+                       hdelta = jiffies - runtime->hw_ptr_jiffies;
+                       if (hdelta > runtime->hw_ptr_buffer_jiffies/2) {
+                               hw_base += runtime->buffer_size;
+                               if (hw_base >= runtime->boundary)
+                                       hw_base = 0;
+                               new_hw_ptr = hw_base + pos;
+                               goto __delta;
+                       }
                }
        }
        /* new_hw_ptr might be lower than old_hw_ptr in case when */

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 134fc6c2e08dc01eeda84a730545b0532f0588fe..e2e73895db122261843b53943b87bf2e2723480c 100644 (file)
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -864,6 +864,8 @@ static void snd_pcm_post_start(struct snd_pcm_substream *substream, int state)
        struct snd_pcm_runtime *runtime = substream->runtime;
        snd_pcm_trigger_tstamp(substream);
        runtime->hw_ptr_jiffies = jiffies;
+       runtime->hw_ptr_buffer_jiffies = (runtime->buffer_size * HZ) / 
+                                                           runtime->rate;
        runtime->status->state = state;
        if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
            runtime->silence_size > 0)