3 files changed, 19 insertions, 2 deletions

diff --git a/Documentation/sound/alsa/Procfile.txt b/Documentation/sound/alsa/Procfile.txt
index bba2dbb79d81..cfac20cf9e33 100644
--- a/Documentation/sound/alsa/Procfile.txt
+++ b/Documentation/sound/alsa/Procfile.txt
@@ -104,6 +104,11 @@ card*/pcm*/xrun_debug
         When this value is greater than 1, the driver will show the
         stack trace additionally.  This may help the debugging.
 
+        Since 2.6.30, this option also enables the hwptr check using
+        jiffies.  This detects spontaneous invalid pointer callback
+        values, but can be lead to too much corrections for a (mostly
+        buggy) hardware that doesn't give smooth pointer updates.
+
 card*/pcm*/sub*/info
         The general information of this PCM sub-stream.
 
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index a2a792c18c40..d659995ac3ac 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -249,6 +249,11 @@ static int snd_pcm_update_hw_ptr_interrupt(struct snd_pcm_substream *substream)
                         new_hw_ptr = hw_base + pos;
                 }
         }
+
+        /* Do jiffies check only in xrun_debug mode */
+        if (!xrun_debug(substream))
+                goto no_jiffies_check;
+
         /* Skip the jiffies check for hardwares with BATCH flag.
          * Such hardware usually just increases the position at each IRQ,
          * thus it can't give any strange position.
@@ -336,7 +341,9 @@ int snd_pcm_update_hw_ptr(struct snd_pcm_substream *substream)
                         hw_base = 0;
                 new_hw_ptr = hw_base + pos;
         }
-        if (((delta * HZ) / runtime->rate) > jdelta + HZ/100) {
+        /* Do jiffies check only in xrun_debug mode */
+        if (xrun_debug(substream) &&
+            ((delta * HZ) / runtime->rate) > jdelta + HZ/100) {
                 hw_ptr_error(substream,
                              "hw_ptr skipping! "
                              "(pos=%ld, delta=%ld, period=%ld, jdelta=%lu/%lu)\n",
@@ -1478,7 +1485,6 @@ static int snd_pcm_lib_ioctl_reset(struct snd_pcm_substream *substream,
                 runtime->status->hw_ptr %= runtime->buffer_size;
         else
                 runtime->status->hw_ptr = 0;
-        runtime->hw_ptr_jiffies = jiffies;
         snd_pcm_stream_unlock_irqrestore(substream, flags);
         return 0;
 }
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index fc6f98e257df..b5da656d1ece 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -848,6 +848,7 @@ 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->status->state = state;
         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
             runtime->silence_size > 0)
@@ -961,6 +962,11 @@ static int snd_pcm_do_pause(struct snd_pcm_substream *substream, int push)
 {
         if (substream->runtime->trigger_master != substream)
                 return 0;
+        /* The jiffies check in snd_pcm_update_hw_ptr*() is done by
+         * a delta betwen the current jiffies, this gives a large enough
+         * delta, effectively to skip the check once.
+         */
+        substream->runtime->hw_ptr_jiffies = jiffies - HZ * 1000;
         return substream->ops->trigger(substream,
                                        push ? SNDRV_PCM_TRIGGER_PAUSE_PUSH :
                                               SNDRV_PCM_TRIGGER_PAUSE_RELEASE);