linux-kernel - Re: [PATCH] fsl_ifc_nand: fix handing of bit flips in erased nand

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Date:   Wed, 17 May 2017 15:00:59 +0200
From:   Pavel Machek <pavel@....cz>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     richard@....at, dwmw2@...radead.org, computersforpeace@...il.com,
        marek.vasut@...il.com, cyrille.pitchen@...el.com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mark.marshall@...cronenergy.com, b44839@...escale.com,
        prabhakar@...escale.com
Subject: Re: [PATCH] fsl_ifc_nand: fix handing of bit flips in erased nand

Hi!

> On Wed, 17 May 2017 14:22:24 +0200
> Pavel Machek <pavel@....cz> wrote:
> 
> > If we see unrecoverable ECC error, we need to count number of bitflips
> > from all-ones and report correctable/uncorrectable according to
> > that. Otherwise we report ECC failed on erased flash with single bit error.
> > 
> > Signed-off-by: Pavel Machek <pavel@...x.de>
> > 
> > @@ -678,6 +648,41 @@ static int fsl_ifc_wait(struct mtd_info *mtd, struct nand_chip *chip)
> >  	return nand_fsr | NAND_STATUS_WP;
> >  }
> >  
> > +/*
> > + * The controller does not check for bitflips in erased pages,
> > + * therefore software must check instead.
> > + */
> > +static int check_erased_page(struct nand_chip *chip, u8 *buf)
> > +{
> > +	struct mtd_info *mtd = nand_to_mtd(chip);
> > +	u8 *ecc = chip->oob_poi;
> > +	const int ecc_size = chip->ecc.bytes;
> > +	const int pkt_size = chip->ecc.size;
> > +	int i, res, bitflips = 0;
> > +	struct mtd_oob_region oobregion = { };
> > +
> > +	mtd_ooblayout_ecc(mtd, 0, &oobregion);
> > +	ecc += oobregion.offset;
> > +
> > +	for (i = 0; i < chip->ecc.steps; ++i) {
> > +		res = nand_check_erased_ecc_chunk(buf, pkt_size, ecc, ecc_size,
> > +						  NULL, 0,
> > +						  chip->ecc.strength);
> > +		if (res < 0)
> > +			mtd->ecc_stats.failed++;
> > +		else
> > +			mtd->ecc_stats.corrected += res;
> > +
> > +		bitflips = max(res, bitflips);
> > +		buf += pkt_size;
> > +		ecc += ecc_size;
> > +	}
> > +
> > +	mtd_ooblayout_ecc(mtd, 1, &oobregion);
> 
> Why is this needed?

It is not, will remove.

> > @@ -904,6 +922,21 @@ static int fsl_ifc_chip_init(struct fsl_ifc_mtd *priv)
> >  		chip->ecc.algo = NAND_ECC_HAMMING;
> >  	}
> >  
> > +	{
> > +		struct mtd_oob_region oobregion = { };
> > +
> > +		mtd_ooblayout_ecc(mtd, 0, &oobregion);
> > +		if (!oobregion.length) {
> > +			dev_err(priv->dev, "No ECC in oobregion?\n");
> > +			return -EINVAL;
> > +		}
> > +		mtd_ooblayout_ecc(mtd, 1, &oobregion);
> > +		if (oobregion.length) {
> > +			dev_err(priv->dev, "Extra data in oobregion?\n");
> > +			return -EINVAL;
> > +		}
> > +	}
> 
> This clearly doesn't belong in this patch. And if you really want to
> check that, please create a separate function instead of defining a
> non-conditional code block inside fsl_ifc_chip_init().

I am not sure I want to check that. check_erased_page() can only
handle layout with just one oobregion. If you think check is not
needed, I'll happily remove the checking.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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