mtd: nand: fix Samsung SLC NAND identification regression

A combination of the following two commits caused a regression in 3.7-rc1
when identifying some Samsung NAND, so that some previously working NAND
were no longer detected properly:

    commit e3b88bd604283ef83ae6e8f53622d5b1ffe9d43a
    mtd: nand: add generic READ ID length calculation functions

    commit e2d3a35ee427aaba99b6c68a56609ce276c51270
    mtd: nand: detect Samsung K9GBG08U0A, K9GAG08U0F ID

Particularly, a regression was seen on Samsung K9F2G08U0B, with the
following full 8-byte READ ID string:

    ec da 10 95 44 00 ec da

The basic problem is that Samsung manufactures both SLC and MLC NAND
that use a non-standard decoding table for deriving information from
their IDs. I have heuristically determined that all the chips that use
the new table have ID strings which wrap around after the 6th byte.
Unfortunately, I overlooked the fact that some older Samsung SLC (which
use a different decoding table) have "5 byte ID strings" which also wrap
around after the 6th byte.

This patch re-introduces a distinction between these old and new Samsung
NAND by checking that the 6th byte is non-zero, allowing both old and
new Samsung NAND to be detected properly.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Tested-by: Brian Norris <computersforpeace@gmail.com>
Reported-by: Marek Vasut <marex@denx.de>
Tested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index ec6841d8e956..d5ece6ea6f98 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -2983,13 +2983,14 @@ static void nand_decode_ext_id(struct mtd_info *mtd, struct nand_chip *chip,
         /*
          * Field definitions are in the following datasheets:
          * Old style (4,5 byte ID): Samsung K9GAG08U0M (p.32)
-         * New style   (6 byte ID): Samsung K9GAG08U0F (p.44)
+         * New Samsung (6 byte ID): Samsung K9GAG08U0F (p.44)
          * Hynix MLC   (6 byte ID): Hynix H27UBG8T2B (p.22)
          *
-         * Check for ID length, cell type, and Hynix/Samsung ID to decide what
-         * to do.
+         * Check for ID length, non-zero 6th byte, cell type, and Hynix/Samsung
+         * ID to decide what to do.
          */
-        if (id_len == 6 && id_data[0] == NAND_MFR_SAMSUNG) {
+        if (id_len == 6 && id_data[0] == NAND_MFR_SAMSUNG &&
+                        id_data[5] != 0x00) {
                 /* Calc pagesize */
                 mtd->writesize = 2048 << (extid & 0x03);
                 extid >>= 2;