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>

2 files changed, 11 insertions, 5 deletions

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index e9d98be190c5..d6ecca27bb68 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -329,11 +329,15 @@ 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 303ac04ff6e4..2d2e1b65ee9a 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -867,6 +867,8 @@ 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)