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    SubjectRe: [PATCH] mtd: nand: Properly initialize 'mtd->bitflip_threshold' prior 'scan_bbt()' is invoked
    On Fri, Jun 08, 2012 at 06:29:06PM +0300, Shmulik Ladkani wrote:
    > 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 <s.hauer@pengutronix.de>
    > Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
    > ---
    > - 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?

    Sure, that's ok.

    > - Sascha, care to test and verify it works for your system?

    Yes, this puts my system back to work

    Tested-by: Sascha Hauer <s.hauer@pengutronix.de>


    >
    > 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)
    > --
    > 1.7.5.4
    >

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