[U-Boot] [PATCH 4/5] mtd: nand: Use ECC for NAND write verification

[Peter Tyser]

From: Joe Schaack <jschaack at xes-inc.com>

Modify the nand_write_page() function to use ECC when appropriate to verify
writes.  Previously if a single bit error occured and software ECC was
used the write verification would report a failure.  However, the write
really did succeed, since ECC can handle the error.

The issue can be simulated with a sequence of commands such as:

   # Inject a fake bit that is stuck low (2K page flash being used)
   nand erase 0 0x20000
   mw.b 0x10000 0xff 0x1000
   mw.b 0x10000 0xfe 1
   nand write.raw 0x10000 0x0 0x1

   # Write some data which needs to toggle the fake stuck bit
   mw.b 0x10000 0xab 1
   nand write 0x10000 0x0 0x800

An error will occur:
    NAND write: device 0 offset 0x0, size 0x800
    NAND write to offset 0 failed -5
    0 bytes written: ERROR

But you can verify data was correctly written:
    # Show data is correct when ECC is used
    nand read 0x10000 0x0 0x800
    md 0x10000

    # Show the bit is still stuck low
    nand read.raw 0x10000 0x0 0x1
    md 0x10000

Change the behavior so ECC is used when verifying non-raw writes.
This only impacts boards that have COFNIG_MTD_NAND_VERIFY_WRITE
defined.

Signed-off-by: Joe Schaack <jschaack at xes-inc.com>
Signed-off-by: Peter Tyser <ptyser at xes-inc.com>
---

 drivers/mtd/nand/nand_base.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index abcb84a..aa039ef 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -2405,7 +2405,10 @@ static int nand_write_page(struct mtd_info *mtd, struct nand_chip *chip,
 
 	/* Send command to read back the data */
 	chip->cmdfunc(mtd, NAND_CMD_READ0, 0, page);
-	chip->ecc.read_page_raw(mtd, chip, vfy_buf, oob_required, page);
+	if (unlikely(raw))
+		chip->ecc.read_page_raw(mtd, chip, vfy_buf, oob_required, page);
+	else
+		chip->ecc.read_page(mtd, chip, vfy_buf, oob_required, page);
 
 	status = memcmp(buf, vfy_buf, mtd->writesize);
 
-- 
1.9.1