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>

3 files changed, 17 insertions, 7 deletions

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index bcb7f05fd27b..d0eaef67b9bb 100644
--- a/drivers/mtd/mtdchar.c
+++ b/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;
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index b61a7c7bd097..ad40607f5f24 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/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;
 
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index c7113a9cd66d..0b3d464cba13 100644
--- a/include/linux/mtd/nand.h
+++ b/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,