[PATCH v3] mtd: rawnand: micron: handle on-die "ECC-off" devices correctly

[Marco Felsch <m.felsch@pengutronix.de>]

Some devices are not supposed to support on-die ECC but experience
shows that internal ECC machinery can actually be enabled through the
"SET FEATURE (EFh)" command, even if a read of the "READ ID Parameter
Tables" returns that it is not.

Currently, the driver checks the "READ ID Parameter" field directly
after having enabled the feature. If the check fails it returns
immediately but leaves the ECC on. When using buggy chips like
MT29F2G08ABAGA and MT29F2G08ABBGA, all future read/program cycles will
go through the on-die ECC, confusing the host controller which is
supposed to be the one handling correction.

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

Cc: stable@vger.kernel.org
Fixes: dbc44edbf833 ("mtd: rawnand: micron: Fix on-die ECC detection logic")
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
---
 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..8ca9fad6e6ad 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 officially.
+	 * 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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