mtd: nand: initialize bitflip_threshold prior to BBT scanning

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=ea3b2ea24ef0f2ef9c6795b19cff456195b6728a
Commit:     ea3b2ea24ef0f2ef9c6795b19cff456195b6728a
Parent:     cfaf025112d3856637ff34a767ef785ef5cf2ca9
Author:     Shmulik Ladkani <shmulik at jungo.com>
AuthorDate: Fri Jun 8 18:29:06 2012 +0300
Committer:  David Woodhouse <David.Woodhouse at intel.com>
CommitDate: Sat Jun 9 12:02:04 2012 +0100

    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 at pengutronix.de>
    Tested-by: Sascha Hauer <s.hauer at pengutronix.de>
    Signed-off-by: Shmulik Ladkani <shmulik.ladkani at gmail.com>
    Signed-off-by: Artem Bityutskiy <artem.bityutskiy at linux.intel.com>
    Signed-off-by: David Woodhouse <David.Woodhouse at intel.com>
---
 drivers/mtd/nand/nand_base.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index d47586c..a11253a 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)