mtd: support reading OOB without ECC

This fixes issues with `nanddump -n' and the MEMREADOOB[64] ioctls on
hardware that performs error correction when reading only OOB data. A
driver for such hardware needs to know when we're doing a RAW vs. a
normal write, but mtd_do_read_oob does not pass such information to the
lower layers (e.g., NAND). We should pass MTD_OOB_RAW or MTD_OOB_PLACE
based on the MTD file mode.

For now, most drivers can get away with just setting:

  chip->ecc.read_oob_raw = chip->ecc.read_oob

This is done by default; but for systems that behave as described above,
you must supply your own replacement function.

This was tested with nandsim as well as on actual SLC NAND.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Jim Quinlan <jim2101024@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>

drivers/mtd/mtdchar.c

@@ -435,9 +435,11 @@ static int mtd_do_writeoob(struct file *file, struct mtd_info *mtd,
 	return ret;
 }
 
-static int mtd_do_readoob(struct mtd_info *mtd, uint64_t start,
-	uint32_t length, void __user *ptr, uint32_t __user *retp)
+static int mtd_do_readoob(struct file *file, struct mtd_info *mtd,
+	uint64_t start, uint32_t length, void __user *ptr,
+	uint32_t __user *retp)
 {
+	struct mtd_file_info *mfi = file->private_data;
 	struct mtd_oob_ops ops;
 	int ret = 0;
 
@@ -455,7 +457,7 @@ static int mtd_do_readoob(struct mtd_info *mtd, uint64_t start,
 	ops.ooblen = length;
 	ops.ooboffs = start & (mtd->writesize - 1);
 	ops.datbuf = NULL;
-	ops.mode = MTD_OOB_PLACE;
+	ops.mode = (mfi->mode == MTD_MODE_RAW) ? MTD_OOB_RAW : MTD_OOB_PLACE;
 
 	if (ops.ooboffs && ops.ooblen > (mtd->oobsize - ops.ooboffs))
 		return -EINVAL;
@@ -716,7 +718,7 @@ static int mtd_ioctl(struct file *file, u_int cmd, u_long arg)
 		if (copy_from_user(&buf, argp, sizeof(buf)))
 			ret = -EFAULT;
 		else
-			ret = mtd_do_readoob(mtd, buf.start, buf.length,
+			ret = mtd_do_readoob(file, mtd, buf.start, buf.length,
 				buf.ptr, &buf_user->start);
 		break;
 	}
@@ -743,7 +745,7 @@ static int mtd_ioctl(struct file *file, u_int cmd, u_long arg)
 		if (copy_from_user(&buf, argp, sizeof(buf)))
 			ret = -EFAULT;
 		else
-			ret = mtd_do_readoob(mtd, buf.start, buf.length,
+			ret = mtd_do_readoob(file, mtd, buf.start, buf.length,
 				(void __user *)(uintptr_t)buf.usr_ptr,
 				&buf_user->length);
 		break;
@@ -1029,7 +1031,7 @@ static long mtd_compat_ioctl(struct file *file, unsigned int cmd,
 		if (copy_from_user(&buf, argp, sizeof(buf)))
 			ret = -EFAULT;
 		else
-			ret = mtd_do_readoob(mtd, buf.start,
+			ret = mtd_do_readoob(file, mtd, buf.start,
 				buf.length, compat_ptr(buf.ptr),
 				&buf_user->start);
 		break;

drivers/mtd/nand/nand_base.c

@@ -1787,7 +1787,10 @@ static int nand_do_read_oob(struct mtd_info *mtd, loff_t from,
 	page = realpage & chip->pagemask;
 
 	while (1) {
-		sndcmd = chip->ecc.read_oob(mtd, chip, page, sndcmd);
+		if (ops->mode == MTD_OOB_RAW)
+			sndcmd = chip->ecc.read_oob_raw(mtd, chip, page, sndcmd);
+		else
+			sndcmd = chip->ecc.read_oob(mtd, chip, page, sndcmd);
 
 		len = min(len, readlen);
 		buf = nand_transfer_oob(chip, buf, ops, len);
@@ -3385,6 +3388,8 @@ int nand_scan_tail(struct mtd_info *mtd)
 	}
 
 	/* For many systems, the standard OOB write also works for raw */
+	if (!chip->ecc.read_oob_raw)
+		chip->ecc.read_oob_raw = chip->ecc.read_oob;
 	if (!chip->ecc.write_oob_raw)
 		chip->ecc.write_oob_raw = chip->ecc.write_oob;
 

include/linux/mtd/nand.h

@@ -341,6 +341,7 @@ struct nand_hw_control {
  * @write_page:	function to write a page according to the ECC generator
  *		requirements.
  * @write_oob_raw:	function to write chip OOB data without ECC
+ * @read_oob_raw:	function to read chip OOB data without ECC
  * @read_oob:	function to read chip OOB data
  * @write_oob:	function to write chip OOB data
  */
@@ -371,6 +372,8 @@ struct nand_ecc_ctrl {
 			const uint8_t *buf);
 	int (*write_oob_raw)(struct mtd_info *mtd, struct nand_chip *chip,
 			int page);
+	int (*read_oob_raw)(struct mtd_info *mtd, struct nand_chip *chip,
+			int page, int sndcmd);
 	int (*read_oob)(struct mtd_info *mtd, struct nand_chip *chip, int page,
 			int sndcmd);
 	int (*write_oob)(struct mtd_info *mtd, struct nand_chip *chip,