staging: comedi: comedidev.h: document struct comedi_lrange

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/comedidev.h

@@ -606,6 +606,17 @@ extern const struct comedi_lrange range_unknown;
 #define GCC_ZERO_LENGTH_ARRAY 0
 #endif
 
+/**
+ * struct comedi_lrange - Describes a COMEDI range table
+ * @length: Number of entries in the range table.
+ * @range: Array of &struct comedi_krange, one for each range.
+ *
+ * Each element of @range[] describes the minimum and maximum physical range
+ * range and the type of units.  Typically, the type of unit is %UNIT_volt
+ * (i.e. volts) and the minimum and maximum are in millionths of a volt.
+ * There may also be a flag that indicates the minimum and maximum are merely
+ * scale factors for an unknown, external reference.
+ */
 struct comedi_lrange {
 	int length;
 	struct comedi_krange range[GCC_ZERO_LENGTH_ARRAY];