perf/Documentation/ABI -- add some documentation for perf_eventsysfs usage

[Vince Weaver]

Add some documentation for the perf_event related
  /sys/bus/event_source/bus/devices/
files, since in theory it's a stable interface and the only
current documentation is some lex and yacc files in the
perf tools directory.

Signed-off-by: Vince Weaver <vincent.weaver@xxxxxxxxx>

diff --git a/Documentation/ABI/stable/sysfs-bus-event_source-devices b/Documentation/ABI/stable/sysfs-bus-event_source-devices
new file mode 100644
index 0000000..9ef862f
--- /dev/null
+++ b/Documentation/ABI/stable/sysfs-bus-event_source-devices
@@ -0,0 +1,39 @@
+What:		/sys/bus/event_source/bus/devices/*/events/*
+Date:		Oct 2012
+KernelVersion:	3.8
+Contact:	Jiri Olsa <jolsa@xxxxxxxxxx>
+Description:
+		Each file in /sys/bus/event_source/bus/devices/*/events/
+		represents a predefined perf_event event.
+
+		The contents of the file are a string describing
+		fields to set when generating raw events for
+		the perf_event_open() system call.
+
+		The layout of the file is
+			attr=value[,attr=value]...
+		Where attr is the name of a bitfield described
+		in /sys/bus/event_source/bus/devices/*/format/*
+		and value is either a hex (starting with 0x) or decimal
+		value.
+
+
+What:		/sys/bus/event_source/bus/devices/*/format/*
+Date:		Oct 2012
+KernelVersion:	3.8
+Contact:	Jiri Olsa <jolsa@xxxxxxxxxx>
+Description:
+		Each file in /sys/bus/event_source/bus/devices/*/format/
+		represents a description of a bitfield used when 
+		constructing raw perf_event_open() raw events.
+
+		The contents of the file are a string describing
+		the name of the field and its range.
+
+		The layout of the file is
+			field:low[-high]
+		Where field is the field name, low is the low bit
+		of the range, and the optional high value is the high
+		bit of the range.  The low and high values are base-10
+		integers.
+
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