mtd: add ECC info for nand_flash_dev{}

Add an instance of an anonymous struct to store the ECC info for full id
nand chips.
	@ecc.strength_ds: ECC correctability from the datasheet.
	@ecc.step_ds: ECC size required by the @ecc.strength_ds,

These two fields are all from the datasheet.

Also add the necessary macros to make the code simple and clean.
Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

include/linux/mtd/nand.h

@@ -628,6 +628,11 @@ struct nand_chip {
 	{ .name = (nm), {{ .dev_id = (devid) }}, .chipsize = (chipsz), \
 	  .options = (opts) }
 
+#define NAND_ECC_INFO(_strength, _step)	\
+			{ .strength_ds = (_strength), .step_ds = (_step) }
+#define NAND_ECC_STRENGTH(type)		((type)->ecc.strength_ds)
+#define NAND_ECC_STEP(type)		((type)->ecc.step_ds)
+
 /**
  * struct nand_flash_dev - NAND Flash Device ID Structure
  * @name: a human-readable name of the NAND chip
@@ -645,6 +650,12 @@ struct nand_chip {
  * @options: stores various chip bit options
  * @id_len: The valid length of the @id.
  * @oobsize: OOB size
+ * @ecc.strength_ds: The ECC correctability from the datasheet, same as the
+ *                   @ecc_strength_ds in nand_chip{}.
+ * @ecc.step_ds: The ECC step required by the @ecc.strength_ds, same as the
+ *               @ecc_step_ds in nand_chip{}, also from the datasheet.
+ *               For example, the "4bit ECC for each 512Byte" can be set with
+ *               NAND_ECC_INFO(4, 512).
  */
 struct nand_flash_dev {
 	char *name;
@@ -661,6 +672,10 @@ struct nand_flash_dev {
 	unsigned int options;
 	uint16_t id_len;
 	uint16_t oobsize;
+	struct {
+		uint16_t strength_ds;
+		uint16_t step_ds;
+	} ecc;
 };
 
 /**