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>

1 files changed, 5 insertions, 0 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.