ALSA: pcm - Update document about xrun_debug proc file

	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.