From bd76af0f87f7a1815b311bde269a3f18305b3169 Mon Sep 17 00:00:00 2001
From: Jaroslav Kysela <perex@perex.cz>
Date: Wed, 18 Aug 2010 14:16:54 +0200
Subject: 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 85f1c6b..dfd9b76 100644
--- 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 e23e0e7..a1707cc 100644
--- 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 134fc6c..e2e7389 100644
--- 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)
-- 
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