mtd: create an mtd_ooblayout_ops struct to ease ECC layout definition

ECC layout definitions are currently exposed using the nand_ecclayout
struct which embeds oobfree and eccpos arrays with predefined size.
This approach was acceptable when NAND chips were providing relatively
small OOB regions, but MLC and TLC now provide OOB regions of several
hundreds of bytes, which implies a non negligible overhead for everybody
even those who only need to support legacy NANDs.

Create an mtd_ooblayout_ops interface providing the same functionality
(expose the ECC and oobfree layout) without the need for this huge
structure.

The mtd->ecclayout is now deprecated and should be replaced by the
equivalent mtd_ooblayout_ops. In the meantime we provide a wrapper around
the ->ecclayout field to ease migration to this new model.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

1 files changed, 28 insertions, 4 deletions

diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index e62da8462493..177bf314ad70 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -101,6 +101,9 @@ struct mtd_oob_ops {
  * similar, smaller struct nand_ecclayout_user (in mtd-abi.h) that is retained
  * for export to user-space via the ECCGETLAYOUT ioctl.
  * nand_ecclayout should be expandable in the future simply by the above macros.
+ *
+ * This structure is now deprecated, you should use struct nand_ecclayout_ops
+ * to describe your OOB layout.
  */
 struct nand_ecclayout {
         __u32 eccbytes;
@@ -123,6 +126,22 @@ struct mtd_oob_region {
         u32 length;
 };
 
+/*
+ * struct mtd_ooblayout_ops - NAND OOB layout operations
+ * @ecc: function returning an ECC region in the OOB area.
+ *       Should return -ERANGE if %section exceeds the total number of
+ *       ECC sections.
+ * @free: function returning a free region in the OOB area.
+ *        Should return -ERANGE if %section exceeds the total number of
+ *        free sections.
+ */
+struct mtd_ooblayout_ops {
+        int (*ecc)(struct mtd_info *mtd, int section,
+                   struct mtd_oob_region *oobecc);
+        int (*free)(struct mtd_info *mtd, int section,
+                    struct mtd_oob_region *oobfree);
+};
+
 struct module;  /* only needed for owner field in mtd_info */
 
 struct mtd_info {
@@ -181,9 +200,12 @@ struct mtd_info {
         const char *name;
         int index;
 
-        /* ECC layout structure pointer - read only! */
+        /* [Deprecated] ECC layout structure pointer - read only! */
         struct nand_ecclayout *ecclayout;
 
+        /* OOB layout description */
+        const struct mtd_ooblayout_ops *ooblayout;
+
         /* the ecc step size. */
         unsigned int ecc_step_size;
 
@@ -286,10 +308,12 @@ int mtd_ooblayout_set_databytes(struct mtd_info *mtd, const u8 *databuf,
 int mtd_ooblayout_count_freebytes(struct mtd_info *mtd);
 int mtd_ooblayout_count_eccbytes(struct mtd_info *mtd);
 
-static inline void mtd_set_ecclayout(struct mtd_info *mtd,
-                                     struct nand_ecclayout *ecclayout)
+void mtd_set_ecclayout(struct mtd_info *mtd, struct nand_ecclayout *ecclayout);
+
+static inline void mtd_set_ooblayout(struct mtd_info *mtd,
+                                     const struct mtd_ooblayout_ops *ooblayout)
 {
-        mtd->ecclayout = ecclayout;
+        mtd->ooblayout = ooblayout;
 }
 
 static inline void mtd_set_of_node(struct mtd_info *mtd,