[PATCH] mtd: rawnand: micron: handle "ecc off" devices correctly

[Marco Felsch <m.felsch@xxxxxxxxxxxxxx>]

Some devices don't support ecc "official". By "official" I mean that the
feature can be set trough the "SET FEATURE (EFh)" command but isn't
reported to the "READ ID Parameter Tables". Because the "ECC Field"
still says that it is disabled. This is applicable at least
for the MT29F2G08ABAGA and MT29F2G08ABBGA devices. Even worse the
datasheet describes the ECC feature in chapter "ECC Protection".

Currently the driver checks the "READ ID Parameter" field directly after
we enabled the feature. If the check fails we return immediately but
leave the ECC on. Now all future read/program cycles goes trough the ecc
and the host nfc gets confused and reports ECC errors.

To address this in a common way we need to turn off the ECC directly
after reading the "READ ID Parameter" and before checking the
"ECC status".

Signed-off-by: Marco Felsch <m.felsch@xxxxxxxxxxxxxx>
---
 drivers/mtd/nand/raw/nand_micron.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
index 1622d3145587..fb199ad2f1a6 100644
--- a/drivers/mtd/nand/raw/nand_micron.c
+++ b/drivers/mtd/nand/raw/nand_micron.c
@@ -390,6 +390,14 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
 	    (chip->id.data[4] & MICRON_ID_INTERNAL_ECC_MASK) != 0x2)
 		return MICRON_ON_DIE_UNSUPPORTED;
 
+	/*
+	 * It seems that there are devices which do not support ECC official.
+	 * At least the MT29F2G08ABAGA / MT29F2G08ABBGA devices supports
+	 * enabling the ECC feature but don't reflect that to the READ_ID table.
+	 * So we have to guarantee that we disable the ECC feature directly
+	 * after we did the READ_ID table command. Later we can evaluate the
+	 * ECC_ENABLE support.
+	 */
 	ret = micron_nand_on_die_ecc_setup(chip, true);
 	if (ret)
 		return MICRON_ON_DIE_UNSUPPORTED;
@@ -398,13 +406,13 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
 	if (ret)
 		return MICRON_ON_DIE_UNSUPPORTED;
 
-	if (!(id[4] & MICRON_ID_ECC_ENABLED))
-		return MICRON_ON_DIE_UNSUPPORTED;
-
 	ret = micron_nand_on_die_ecc_setup(chip, false);
 	if (ret)
 		return MICRON_ON_DIE_UNSUPPORTED;
 
+	if (!(id[4] & MICRON_ID_ECC_ENABLED))
+		return MICRON_ON_DIE_UNSUPPORTED;
+
 	ret = nand_readid_op(chip, 0, id, sizeof(id));
 	if (ret)
 		return MICRON_ON_DIE_UNSUPPORTED;
-- 
2.20.1


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