mtd: nand: expand nand_ecc_layout, deprecate ioctl ECCGETLAYOUT

struct nand_ecclayout is too small for many new chips; OOB regions can be as
large as 448 bytes and may increase more in the future. Thus, copying that
struct to user-space with the ECCGETLAYOUT ioctl is not a good idea; the ioctl
would have to be updated every time there's a change to the current largest
size.

Instead, the old nand_ecclayout is renamed to nand_ecclayout_user and a
new struct nand_ecclayout is created that can accomodate larger sizes and
expand without affecting the user-space. struct nand_ecclayout can still
be used in board drivers without modification -- at least for now.

A new function is provided to convert from the new to the old in order to
allow the deprecated ioctl to continue to work with truncated data. Perhaps
the ioctl, the conversion process, and the struct nand_ecclayout_user can be
removed altogether in the future.

Note: There are comments in nand/davinci_nand.c::nand_davinci_probe()
regarding this issue; this driver (and maybe others) can be updated to
account for extra space. All kernel drivers can use the expanded
nand_ecclayout as a drop-in replacement and ignore its benefits.

Signed-off-by: Brian Norris <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/mtdchar.c

···
 	return ret;
 }
 
+/*
+ * Copies (and truncates, if necessary) data from the larger struct,
+ * nand_ecclayout, to the smaller, deprecated layout struct,
+ * nand_ecclayout_user. This is necessary only to suppport the deprecated
+ * API ioctl ECCGETLAYOUT while allowing all new functionality to use
+ * nand_ecclayout flexibly (i.e. the struct may change size in new
+ * releases without requiring major rewrites).
+ */
+static int shrink_ecclayout(const struct nand_ecclayout *from,
+		struct nand_ecclayout_user *to)
+{
+	int i;
+
+	if (!from || !to)
+		return -EINVAL;
+
+	memset(to, 0, sizeof(*to));
+
+	to->eccbytes = min((int)from->eccbytes, MTD_MAX_ECCPOS_ENTRIES_OLD);
+	for (i = 0; i < to->eccbytes; i++)
+		to->eccpos[i] = from->eccpos[i];
+
+	for (i = 0; i < MTD_MAX_OOBFREE_ENTRIES; i++) {
+		if (from->oobfree[i].length == 0 &&
+				from->oobfree[i].offset == 0)
+			break;
+		to->oobavail += from->oobfree[i].length;
+		to->oobfree[i] = from->oobfree[i];
+	}
+
+	return 0;
+}
+
 static int mtd_ioctl(struct file *file, u_int cmd, u_long arg)
 {
 	struct mtd_file_info *mfi = file->private_data;
···
 	}
 #endif
 
+	/* This ioctl is being deprecated - it truncates the ecc layout */
 	case ECCGETLAYOUT:
 	{
+		struct nand_ecclayout_user *usrlay;
+
 		if (!mtd->ecclayout)
 			return -EOPNOTSUPP;
 
-		if (copy_to_user(argp, mtd->ecclayout,
-				 sizeof(struct nand_ecclayout)))
-			return -EFAULT;
+		usrlay = kmalloc(sizeof(*usrlay), GFP_KERNEL);
+		if (!usrlay)
+			return -ENOMEM;
+
+		shrink_ecclayout(mtd->ecclayout, usrlay);
+
+		if (copy_to_user(argp, usrlay, sizeof(*usrlay)))
+			ret = -EFAULT;
+		kfree(usrlay);
 		break;
 	}
 

drivers/mtd/nand/davinci_nand.c

···
 		 * breaks userspace ioctl interface with mtd-utils. Once we
 		 * resolve this issue, NAND_ECC_HW_OOB_FIRST mode can be used
 		 * for the 4KiB page chips.
+		 *
+		 * TODO: Note that nand_ecclayout has now been expanded and can
+		 *  hold plenty of OOB entries.
 		 */
 		dev_warn(&pdev->dev, "no 4-bit ECC support yet "
 				"for 4KiB-page NAND\n");

include/linux/mtd/mtd.h

···
 	uint8_t		*oobbuf;
 };
 
+#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.
+ */
+struct nand_ecclayout {
+	__u32 eccbytes;
+	__u32 eccpos[MTD_MAX_ECCPOS_ENTRIES_LARGE];
+	__u32 oobavail;
+	struct nand_oobfree oobfree[MTD_MAX_OOBFREE_ENTRIES_LARGE];
+};
+
 struct mtd_info {
 	u_char type;
 	uint32_t flags;

include/linux/mtd/partitions.h

···
 	uint64_t size;			/* partition size */
 	uint64_t offset;		/* offset within the master MTD space */
 	uint32_t mask_flags;		/* master MTD flags to mask out for this partition */
-	struct nand_ecclayout *ecclayout;	/* out of band layout for this partition (NAND only)*/
+	struct nand_ecclayout *ecclayout;	/* out of band layout for this partition (NAND only) */
 };
 
 #define MTDPART_OFS_NXTBLK	(-2)

include/mtd/mtd-abi.h

···
 #define OTPGETREGIONCOUNT	_IOW('M', 14, int)
 #define OTPGETREGIONINFO	_IOW('M', 15, struct otp_info)
 #define OTPLOCK			_IOR('M', 16, struct otp_info)
-#define ECCGETLAYOUT		_IOR('M', 17, struct nand_ecclayout)
+#define ECCGETLAYOUT		_IOR('M', 17, struct nand_ecclayout_user)
 #define ECCGETSTATS		_IOR('M', 18, struct mtd_ecc_stats)
 #define MTDFILEMODE		_IO('M', 19)
 #define MEMERASE64		_IOW('M', 20, struct erase_info_user64)
···
  * ECC layout control structure. Exported to userspace for
  * diagnosis and to allow creation of raw images
  */
-struct nand_ecclayout {
+struct nand_ecclayout_user {
 	__u32 eccbytes;
 	__u32 eccpos[64];
 	__u32 oobavail;

include/mtd/mtd-user.h

···
 typedef struct erase_info_user erase_info_t;
 typedef struct region_info_user region_info_t;
 typedef struct nand_oobinfo nand_oobinfo_t;
-typedef struct nand_ecclayout nand_ecclayout_t;
+typedef struct nand_ecclayout_user nand_ecclayout_t;
 
 #endif /* __MTD_USER_H__ */