Extcon: support mutually exclusive relation between cables.

There could be cables that t recannot be attaches simulatenously. Extcon
device drivers may express such information via mutually_exclusive in
struct extcon_dev.

For example, for an extcon device with 16 cables (bits 0 to 15 are
available), if mutually_exclusive = { 0x7, 0xC0, 0x81, 0 }, then, the
following attachments are prohibitted.
{0, 1}
{0, 2}
{1, 2}
{6, 7}
{0, 7}
and every attachment set that are superset of one of the above.
For the detail, please refer to linux/include/linux/extcon.h.

The concept is suggested by NeilBrown <neilb@suse.de>

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

--
Changes from V5:
- Updated sysfs format
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-class-extcon

@@ -15,6 +15,10 @@ Description:
 		may have both HDMI and Charger attached, or analog audio,
 		video, and USB cables attached simulteneously.
 
+		If there are cables mutually exclusive with each other,
+		such binary relations may be expressed with extcon_dev's
+		mutually_exclusive array.
+
 What:		/sys/class/extcon/.../name
 Date:		February 2012
 Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
@@ -73,3 +77,21 @@ Description:
 		state of cable "x" (integer between 0 and 31) of an extcon
 		device. The state value is either 0 (detached) or 1
 		(attached).
+
+What:		/sys/class/extcon/.../mutually_exclusive/...
+Date:		December 2011
+Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
+Description:
+		Shows the relations of mutually exclusiveness. For example,
+		if the mutually_exclusive array of extcon_dev is
+		{0x3, 0x5, 0xC, 0x0}, the, the output is:
+		# ls mutually_exclusive/
+		0x3
+		0x5
+		0xc
+		#
+
+		Note that mutually_exclusive is a sub-directory of the extcon
+		device and the file names under the mutually_exclusive
+		directory show the mutually-exclusive sets, not the contents
+		of the files.