Re: fsl_ifc_nand: are blank pages protected by ECC?

Boris Brezillon
2017-04-21T13:49:21Z

On Fri, 21 Apr 2017 15:37:21 +0200
Pavel Machek <pavel@ucw.cz> wrote:

> Hi!
>
> > (Added driver author to the cc list, maybe he can help).
>
> > > > UBIFS complains:
> > > >
> > > > UBIFS error (pid 931): ubifs_scan: corrupt empty space at LEB 282:252630
> > > > UBIFS error (pid 931): ubifs_scanned_corruption: corruption at LEB 282:252630
> > > > UBIFS error (pid 931): ubifs_scanned_corruption: first 1322 bytes from LEB 282:252630
> > > > UBIFS error (pid 931): ubifs_scan: LEB 282 scanning failed
> ...
> > > > is_blank() checks for all 0xff's, so single-bit 0xfe in the data will
> > > > result in_blank() == 0 and uncorrectable error being signaled.
> > > >
> > > > Should the driver be modified somehow?
> > >
> > > Yep, nand_check_erased_ecc_chunk() [1] is here to help you check this
> > > case, unfortunately, it's not directly applicable here, because this
>
> Maybe I figured it out. Unfortunately, it is only compile tested. Does
> it look approximately right?

Yep that's definitely better. Just one thing missing (see below),
otherwise it looks good.

>
> Thanks,
> Pavel
>
> --- a/drivers/mtd/nand/fsl_ifc_nand.c
> +++ b/drivers/mtd/nand/fsl_ifc_nand.c
> @@ -171,32 +171,6 @@ static void set_addr(struct mtd_info *mtd, int column, int page_addr, int oob)
> ifc_nand_ctrl->index += mtd->writesize;
> }
>
> -static int is_blank(struct mtd_info *mtd, unsigned int bufnum)
> -{
> - struct nand_chip *chip = mtd_to_nand(mtd);
> - struct fsl_ifc_mtd *priv = nand_get_controller_data(chip);
> - u8 __iomem *addr = priv->vbase + bufnum * (mtd->writesize * 2);
> - u32 __iomem *mainarea = (u32 __iomem *)addr;
> - u8 __iomem *oob = addr + mtd->writesize;
> - struct mtd_oob_region oobregion = { };
> - int i, section = 0;
> -
> - i = nand_check_erased_buf(&mainarea[i], mtd->writesize, 0);
> - if (i)
> - return 0;
> -
> - mtd_ooblayout_ecc(mtd, section++, &oobregion);
> - while (oobregion.length) {
> - i = nand_check_erased_buf(&oob[oobregion.offset], oobregion.length, 0);
> - if (i)
> - return 0;
> -
> - mtd_ooblayout_ecc(mtd, section++, &oobregion);
> - }
> -
> - return 1;
> -}
> -
> /* returns nonzero if entire page is blank */
> static int check_read_ecc(struct mtd_info *mtd, struct fsl_ifc_ctrl *ctrl,
> u32 *eccstat, unsigned int bufnum)
> @@ -272,16 +246,14 @@ static void fsl_ifc_run_command(struct mtd_info *mtd)
> if (errors == 15) {
> /*
> * Uncorrectable error.
> - * OK only if the whole page is blank.
> + * We'll check for blank pages later.
> *
> * We disable ECCER reporting due to...
> * erratum IFC-A002770 -- so report it now if we
> * see an uncorrectable error in ECCSTAT.
> */
> - if (!is_blank(mtd, bufnum))
> - ctrl->nand_stat |=
> - IFC_NAND_EVTER_STAT_ECCER;
> - break;
> + ctrl->nand_stat |= IFC_NAND_EVTER_STAT_ECCER;
> + printk("NAND flash read: error but continuing.\n");
> }
>
> mtd->ecc_stats.corrected += errors;
> @@ -676,6 +648,40 @@ 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);
> + BUG_ON(oobregion.length);

Probably something you should check at registration time only.

> +
> + return bitflips;
> +}
> +
> static int fsl_ifc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> uint8_t *buf, int oob_required, int page)
> {
> @@ -687,11 +693,23 @@ static int fsl_ifc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> if (oob_required)
> fsl_ifc_read_buf(mtd, chip->oob_poi, mtd->oobsize);
>
> - if (ctrl->nand_stat & IFC_NAND_EVTER_STAT_ECCER)
> - dev_err(priv->dev, "NAND Flash ECC Uncorrectable Error\n");
> -
> if (ctrl->nand_stat != IFC_NAND_EVTER_STAT_OPC)
> mtd->ecc_stats.failed++;
> +
> + if (ctrl->nand_stat & IFC_NAND_EVTER_STAT_ECCER) {
> + int res;
> +
> + if (!oob_required)
> + fsl_ifc_read_buf(mtd, chip->oob_poi, mtd->oobsize);
> +
> + printk("NAND flash: have error (%d)\n", nctrl->max_bitflips);
> + res = check_erased_page(chip, buf);
> + printk("NAND flash: but erased page says %d\n", res);
> +
> + dev_err(priv->dev, "NAND Flash ECC Uncorrectable Error or erased page\n");
> + return res;
> + }
> +
>
> return nctrl->max_bitflips;
> }
>