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

Pavel Machek
2017-05-17T13:01:06Z

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Hi!

> On Wed, 17 May 2017 14:22:24 +0200
> Pavel Machek <pavel@ucw.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@denx.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