ALSA: pcm - Update document about xrun_debug proc file

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

diff --git a/Documentation/sound/alsa/Procfile.txt b/Documentation/sound/alsa/Procfile.txt
index cfac20c..381908d 100644 (file)
--- a/Documentation/sound/alsa/Procfile.txt
+++ b/Documentation/sound/alsa/Procfile.txt
@@ -88,26 +88,34 @@ card*/pcm*/info
        substreams, etc.
 
 card*/pcm*/xrun_debug
-       This file appears when CONFIG_SND_DEBUG=y.
-       This shows the status of xrun (= buffer overrun/xrun) debug of
-       ALSA PCM middle layer, as an integer from 0 to 2.  The value
-       can be changed by writing to this file, such as
-
-                # cat 2 > /proc/asound/card0/pcm0p/xrun_debug
-
-       When this value is greater than 0, the driver will show the
-       messages to kernel log when an xrun is detected.  The debug
-       message is shown also when the invalid H/W pointer is detected
-       at the update of periods (usually called from the interrupt
+       This file appears when CONFIG_SND_DEBUG=y and
+       CONFIG_PCM_XRUN_DEBUG=y.
+       This shows the status of xrun (= buffer overrun/xrun) and
+       invalid PCM position debug/check of ALSA PCM middle layer.
+       It takes an integer value, can be changed by writing to this
+       file, such as
+
+                # cat 5 > /proc/asound/card0/pcm0p/xrun_debug
+
+       The value consists of the following bit flags:
+         bit 0 = Enable XRUN/jiffies debug messages
+         bit 1 = Show stack trace at XRUN / jiffies check
+         bit 2 = Enable additional jiffies check
+
+       When the bit 0 is set, the driver will show the messages to
+       kernel log when an xrun is detected.  The debug message is
+       shown also when the invalid H/W pointer is detected at the
+       update of periods (usually called from the interrupt
        handler).
 
-       When this value is greater than 1, the driver will show the
-       stack trace additionally.  This may help the debugging.
+       When the bit 1 is set, 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
+       Since 2.6.30, this option can enable 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.
+       This feature is enabled via the bit 2.
 
 card*/pcm*/sub*/info
        The general information of this PCM sub-stream.