ALSA: pcm - Update document about xrun_debug proc file

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

1 files changed, 22 insertions, 14 deletions

diff --git a/Documentation/sound/alsa/Procfile.txt b/Documentation/sound/alsa/Procfile.txt
index cfac20cf9e3..381908d8ca4 100644
--- 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.