mtd: edit comments on deprecation of ioctl ECCGETLAYOUT

There were some improvements and additions necessary in the
comments explaining of the expansion of nand_ecclayout, the
introduction of nand_ecclayout_user, and the deprecation of the
ioctl ECCGETLAYOUT.

Also, I found a better placement for the macro MTD_MAX_ECCPOS_ENTRIES;
next to the definition of MTD_MAX_OOBFREE_ENTRIES in mtd-abi.h. The macro
is really only important for the ioctl code (found in drivers/mtd/mtdchar.c)
but since there are small edits being made to the user-space header, I
figured this is a better location.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

2 files changed, 12 insertions, 7 deletions

diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 03a1e954c58..fe8d77ebec1 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -112,11 +112,11 @@ struct mtd_oob_ops {
 
 #define MTD_MAX_OOBFREE_ENTRIES_LARGE   32
 #define MTD_MAX_ECCPOS_ENTRIES_LARGE    448
-#define MTD_MAX_ECCPOS_ENTRIES_OLD      64      /* Previous maximum */
 /*
- * Correct ECC layout control structure. This replaces old nand_ecclayout
- * (mtd-abi.h) that is exported via ECCGETLAYOUT ioctl. It should be expandable
- *  in the future simply by the above macros.
+ * Internal ECC layout control structure. For historical reasons, there is a
+ * 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.
  */
 struct nand_ecclayout {
         __u32 eccbytes;
diff --git a/include/mtd/mtd-abi.h b/include/mtd/mtd-abi.h
index 5bce0838434..a57c4cb7d6b 100644
--- a/include/mtd/mtd-abi.h
+++ b/include/mtd/mtd-abi.h
@@ -144,13 +144,18 @@ struct nand_oobfree {
 };
 
 #define MTD_MAX_OOBFREE_ENTRIES 8
+#define MTD_MAX_ECCPOS_ENTRIES  64
 /*
- * ECC layout control structure. Exported to userspace for
- * diagnosis and to allow creation of raw images
+ * OBSOLETE: ECC layout control structure. Exported to user-space via ioctl
+ * ECCGETLAYOUT for backwards compatbility and should not be mistaken as a
+ * complete set of ECC information. The ioctl truncates the larger internal
+ * structure to retain binary compatibility with the static declaration of the
+ * ioctl. Note that the "MTD_MAX_..._ENTRIES" macros represent the max size of
+ * the user struct, not the MAX size of the internal struct nand_ecclayout.
  */
 struct nand_ecclayout_user {
         __u32 eccbytes;
-        __u32 eccpos[64];
+        __u32 eccpos[MTD_MAX_ECCPOS_ENTRIES];
         __u32 oobavail;
         struct nand_oobfree oobfree[MTD_MAX_OOBFREE_ENTRIES];
 };