[PATCH] mtd: nand: Properly initialize 'mtd->bitflip_threshold' prior 'scan_bbt()' is invoked

[Sascha Hauer]

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 at pengutronix.de>
> Signed-off-by: Shmulik Ladkani <shmulik.ladkani at 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 at 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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