mtd: nand: add ->badblockbits for minimum number of set bits in bad block byte

This can be used to protect against bitflips in that field, but now mostly
for smartmedia.

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

2 files changed, 10 insertions, 4 deletions

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 51dfea1b3ce6..ba29a29bd743 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -364,14 +364,18 @@ static int nand_block_bad(struct mtd_info *mtd, loff_t ofs, int getchip)
                 bad = cpu_to_le16(chip->read_word(mtd));
                 if (chip->badblockpos & 0x1)
                         bad >>= 8;
-                if ((bad & 0xFF) != 0xff)
-                        res = 1;
+                else
+                        bad &= 0xFF;
         } else {
                 chip->cmdfunc(mtd, NAND_CMD_READOOB, chip->badblockpos, page);
-                if (chip->read_byte(mtd) != 0xff)
-                        res = 1;
+                bad = chip->read_byte(mtd);
         }
 
+        if (likely(chip->badblockbits == 8))
+                res = bad != 0xFF;
+        else
+                res = hweight8(bad) < chip->badblockbits;
+
         if (getchip)
                 nand_release_device(mtd);
 
@@ -2884,6 +2888,7 @@ static struct nand_flash_dev *nand_get_flash_type(struct mtd_info *mtd,
         /* Set the bad block position */
         chip->badblockpos = mtd->writesize > 512 ?
                 NAND_LARGE_BADBLOCK_POS : NAND_SMALL_BADBLOCK_POS;
+        chip->badblockbits = 8;
 
         /* Get chip options, preserve non chip based options */
         chip->options &= ~NAND_CHIPOPTIONS_MSK;
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 48bc2c54302c..f2d4a1ac14b8 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -401,6 +401,7 @@ struct nand_chip {
         int             subpagesize;
         uint8_t         cellinfo;
         int             badblockpos;
+        int             badblockbits;
 
         flstate_t       state;