mtd: update the ABI document about the ecc step size

We add a new sys node for ecc step size. So update the ABI document about it.
Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
[Brian: edited description, modified 'ecc_strength']
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

Documentation/ABI/testing/sysfs-class-mtd

@@ -128,9 +128,8 @@ KernelVersion:	3.4
 Contact:	linux-mtd@lists.infradead.org
 Description:
 		Maximum number of bit errors that the device is capable of
-		correcting within each region covering an ecc step.  This will
-		always be a non-negative integer.  Note that some devices will
-		have multiple ecc steps within each writesize region.
+		correcting within each region covering an ECC step (see
+		ecc_step_size).  This will always be a non-negative integer.
 
 		In the case of devices lacking any ECC capability, it is 0.
 
@@ -173,3 +172,15 @@ Description:
 		This is generally applicable only to NAND flash devices with ECC
 		capability.  It is ignored on devices lacking ECC capability;
 		i.e., devices for which ecc_strength is zero.
+
+What:		/sys/class/mtd/mtdX/ecc_step_size
+Date:		May 2013
+KernelVersion:	3.10
+Contact:	linux-mtd@lists.infradead.org
+Description:
+		The size of a single region covered by ECC, known as the ECC
+		step.  Devices may have several equally sized ECC steps within
+		each writesize region.
+
+		It will always be a non-negative integer.  In the case of
+		devices lacking any ECC capability, it is 0.