Re: [V3, 1/2] mtd: brcmnand: Add check for erased page bitflips

Boris Brezillon
2016-06-13T20:07:44Z

On Thu, 9 Jun 2016 17:17:54 -0400
Kamal Dasu <kdasu.kdev@gmail.com> wrote:

> Check for erased page bitflips in a page. And if well within
> threshold return data as all 0xff. Apply sw check for controller
> version < 7.2. Controller vesion >= 7.2 has hw support.
>
> Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>

Applied both.

Thanks,

Boris

> ---
> V3 changes
> Return the max bitflips from a sector within a page
> V2 changes
> Added use of nand_check_erased_ecc_chunk
> Restrict change to older controller < 7.2
> ---
>
> drivers/mtd/nand/brcmnand/brcmnand.c | 62 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 62 insertions(+)
>
> diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
> index b76ad7c..7ee9617 100644
> --- a/drivers/mtd/nand/brcmnand/brcmnand.c
> +++ b/drivers/mtd/nand/brcmnand/brcmnand.c
> @@ -1545,6 +1545,56 @@ static int brcmnand_read_by_pio(struct mtd_info *mtd, struct nand_chip *chip,
> return ret;
> }
>
> +/*
> + * Check a page to see if it is erased (w/ bitflips) after an uncorrectable ECC
> + * error
> + *
> + * Because the HW ECC signals an ECC error if an erase paged has even a single
> + * bitflip, we must check each ECC error to see if it is actually an erased
> + * page with bitflips, not a truly corrupted page.
> + *
> + * On a real error, return a negative error code (-EBADMSG for ECC error), and
> + * buf will contain raw data.
> + * Otherwise, buf gets filled with 0xffs and return the maximum number of
> + * bitflips-per-ECC-sector to the caller.
> + *
> + */
> +static int brcmstb_nand_verify_erased_page(struct mtd_info *mtd,
> + struct nand_chip *chip, void *buf, u64 addr)
> +{
> + int i, sas;
> + void *oob = chip->oob_poi;
> + int bitflips = 0;
> + int page = addr >> chip->page_shift;
> + int ret;
> +
> + if (!buf) {
> + buf = chip->buffers->databuf;
> + /* Invalidate page cache */
> + chip->pagebuf = -1;
> + }
> +
> + sas = mtd->oobsize / chip->ecc.steps;
> +
> + /* read without ecc for verification */
> + chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
> + ret = chip->ecc.read_page_raw(mtd, chip, buf, true, page);
> + if (ret)
> + return ret;
> +
> + for (i = 0; i < chip->ecc.steps; i++, oob += sas) {
> + ret = nand_check_erased_ecc_chunk(buf, chip->ecc.size,
> + oob, sas, NULL, 0,
> + chip->ecc.strength);
> + if (ret < 0)
> + return ret;
> +
> + bitflips = max(bitflips, ret);
> + }
> +
> + return bitflips;
> +}
> +
> static int brcmnand_read(struct mtd_info *mtd, struct nand_chip *chip,
> u64 addr, unsigned int trans, u32 *buf, u8 *oob)
> {
> @@ -1575,6 +1625,18 @@ static int brcmnand_read(struct mtd_info *mtd, struct nand_chip *chip,
> }
>
> if (mtd_is_eccerr(err)) {
> + /*
> + * Controller version 7.2 has hw encoder to detect erased page
> + * bitflips, apply sw verification for older controllers only
> + */
> + if (ctrl->nand_version < 0x0702) {
> + err = brcmstb_nand_verify_erased_page(mtd, chip, buf,
> + addr);
> + /* erased page bitflips corrected */
> + if (err > 0)
> + return err;
> + }
> +
> dev_dbg(ctrl->dev, "uncorrectable error at 0x%llx\n",
> (unsigned long long)err_addr);
> mtd->ecc_stats.failed++;

--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering