mtd: nand: initialize bitflip_threshold prior to BBT scanning

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 to invocation of 'scan_bbt()'.

Reported-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index d47586cf64ce..a11253a0fcab 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -3501,6 +3501,13 @@ 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)