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Subject[PATCH] mtd: nand: Properly initialize 'mtd->bitflip_threshold' prior 'scan_bbt()' is invoked
As of edbc454 [mtd: driver _read() returns max_bitflips; mtd_read()
returns -EUCLEAN], 'mtd->bitflip_threshold' must be set for mtd devices
having ECC, prior any 'mtd_read()' call.
Otherwise, 'mtd_read()' will falsely return -EUCLEAN.

Normally, 'mtd->bitflip_threshold' is initialized when the MTD is added.

However, this is too late for NAND MTDs, as 'scan_bbt()' is invoked
prior the existing initialization of 'mtd->bitflip_threshold'.

This is a problem since 'scan_bbt()' calls 'mtd_read()', in the case
of a flash-based bad block table.
It resulted in a falsely reported bitflips indication during BBT read,
which lead to constant scrubbing of the flash BBT blocks.

Initialize 'mtd->bitflip_threshold' to its default value (if not already
set by the driver), prior invocation of 'scan_bbt()'.

Reported-by: Sascha Hauer <>
Signed-off-by: Shmulik Ladkani <>
- The issue was introduced in 3.5-rc1 and needs to be merged before 3.5
- Sascha, I've credited you as the reporter, is that ok?
- Sascha, care to test and verify it works for your system?

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 61805e7..0a8724e 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -3484,6 +3484,13 @@ int nand_scan_tail(struct mtd_info *mtd)
/* propagate ecc info to mtd_info */
mtd->ecclayout = chip->ecc.layout;
mtd->ecc_strength = chip->ecc.strength;
+ /*
+ * Initialize bitflip_threshold to its default prior scan_bbt() call.
+ * scan_bbt() might invoke mtd_read(), thus bitflip_threshold must be
+ * properly set.
+ */
+ if (!mtd->bitflip_threshold)
+ mtd->bitflip_threshold = mtd->ecc_strength;

/* Check, if we should skip the bad block table scan */
if (chip->options & NAND_SKIP_BBTSCAN)

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