ALSA: Enable PCM hw_ptr_jiffies check only in xrun_debug mode

The PCM hw_ptr jiffies check results sometimes in problems when a
hardware doesn't give smooth hw_ptr updates.  So far, au88x0 and some
other drivers appear not working due to this strict check.
However, this check is a nice debug tool, and the capability should be
still kept.

Hence, we disable this check now as default unless the user enables it
by setting the xrun_debug mode to the specific stream via a proc file.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 13 insertions, 1 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 3eea98a4e65a..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",