mtd: add mtd_ooblayout_xxx() helper functions

In order to make the ecclayout definition completely dynamic we need to
rework the way the OOB layout are defined and iterated.

Create a few mtd_ooblayout_xxx() helpers to ease OOB bytes manipulation
and hide ecclayout internals to their users.
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

include/linux/mtd/mtd.h

@@ -108,6 +108,21 @@ struct nand_ecclayout {
 	struct nand_oobfree oobfree[MTD_MAX_OOBFREE_ENTRIES_LARGE];
 };
 
+/**
+ * struct mtd_oob_region - oob region definition
+ * @offset: region offset
+ * @length: region length
+ *
+ * This structure describes a region of the OOB area, and is used
+ * to retrieve ECC or free bytes sections.
+ * Each section is defined by an offset within the OOB area and a
+ * length.
+ */
+struct mtd_oob_region {
+	u32 offset;
+	u32 length;
+};
+
 struct module;	/* only needed for owner field in mtd_info */
 
 struct mtd_info {
@@ -253,6 +268,24 @@ struct mtd_info {
 	int usecount;
 };
 
+int mtd_ooblayout_ecc(struct mtd_info *mtd, int section,
+		      struct mtd_oob_region *oobecc);
+int mtd_ooblayout_find_eccregion(struct mtd_info *mtd, int eccbyte,
+				 int *section,
+				 struct mtd_oob_region *oobregion);
+int mtd_ooblayout_get_eccbytes(struct mtd_info *mtd, u8 *eccbuf,
+			       const u8 *oobbuf, int start, int nbytes);
+int mtd_ooblayout_set_eccbytes(struct mtd_info *mtd, const u8 *eccbuf,
+			       u8 *oobbuf, int start, int nbytes);
+int mtd_ooblayout_free(struct mtd_info *mtd, int section,
+		       struct mtd_oob_region *oobfree);
+int mtd_ooblayout_get_databytes(struct mtd_info *mtd, u8 *databuf,
+				const u8 *oobbuf, int start, int nbytes);
+int mtd_ooblayout_set_databytes(struct mtd_info *mtd, const u8 *databuf,
+				u8 *oobbuf, int start, int nbytes);
+int mtd_ooblayout_count_freebytes(struct mtd_info *mtd);
+int mtd_ooblayout_count_eccbytes(struct mtd_info *mtd);
+
 static inline void mtd_set_of_node(struct mtd_info *mtd,
 				   struct device_node *np)
 {