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    Subject[PATCH v4 5/6] mtd: rawnand: micron: support 8/512 on-die ECC
    Date
    Micron MT29F1G08ABAFAWP-ITE:F supports an on-die ECC with 8 bits
    per 512 bytes. Add support for this combination.

    Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
    ---
    Changes in v2:
    - New
    Changes in v3:
    - Handle reporting of corrected errors that don't require a rewrite, expand
    comment for the ECC status bits.
    Changes in v4:
    - Use a switch statement for handling ECC status
    - Update ecc_stats.corrected

    drivers/mtd/nand/raw/nand_micron.c | 68 ++++++++++++++++++++----------
    1 file changed, 46 insertions(+), 22 deletions(-)

    diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
    index d30bd4df9b12..f1ecd4986b50 100644
    --- a/drivers/mtd/nand/raw/nand_micron.c
    +++ b/drivers/mtd/nand/raw/nand_micron.c
    @@ -18,10 +18,28 @@
    #include <linux/mtd/rawnand.h>

    /*
    - * Special Micron status bit that indicates when the block has been
    - * corrected by on-die ECC and should be rewritten
    + * Special Micron status bit 3 indicates that the block has been
    + * corrected by on-die ECC and should be rewritten.
    + *
    + * On chips with 8-bit ECC and additional bit can be used to distinguish
    + * cases where a errors were corrected without needing a rewrite
    + *
    + * Bit 4 Bit 3 Bit 0 Description
    + * ----- ----- ----- -----------
    + * 0 0 0 No Errors
    + * 0 0 1 Multiple uncorrected errors
    + * 0 1 0 4 - 6 errors corrected, recommend rewrite
    + * 0 1 1 Reserved
    + * 1 0 0 1 - 3 errors corrected
    + * 1 0 1 Reserved
    + * 1 1 0 7 - 8 errors corrected, recommend rewrite
    */
    -#define NAND_STATUS_WRITE_RECOMMENDED BIT(3)
    +#define NAND_STATUS_MASK (BIT(4) | BIT(3) | BIT(0))
    +#define NAND_STATUS_NO_ERRORS 0
    +#define NAND_STATUS_UNCORRECTABLE BIT(0)
    +#define NAND_STATUS_4_6_CORRECTED BIT(3)
    +#define NAND_STATUS_1_3_CORRECTED BIT(4)
    +#define NAND_STATUS_7_8_CORRECTED (BIT(4) | BIT(3))

    struct nand_onfi_vendor_micron {
    u8 two_plane_read;
    @@ -137,18 +155,31 @@ micron_nand_read_page_on_die_ecc(struct mtd_info *mtd, struct nand_chip *chip,
    if (ret)
    goto out;

    - if (status & NAND_STATUS_FAIL) {
    + /*
    + * The internal ECC doesn't tell us the number of bitflips
    + * that have been corrected, but tells us if it recommends to
    + * rewrite the block. If it's the case, then we pretend we had
    + * a number of bitflips equal to the ECC strength, which will
    + * hint the NAND core to rewrite the block.
    + */
    + switch (status & NAND_STATUS_MASK) {
    + case NAND_STATUS_UNCORRECTABLE:
    mtd->ecc_stats.failed++;
    - } else if (status & NAND_STATUS_WRITE_RECOMMENDED) {
    - /*
    - * The internal ECC doesn't tell us the number of bitflips
    - * that have been corrected, but tells us if it recommends to
    - * rewrite the block. If it's the case, then we pretend we had
    - * a number of bitflips equal to the ECC strength, which will
    - * hint the NAND core to rewrite the block.
    - */
    - mtd->ecc_stats.corrected += chip->ecc.strength;
    + break;
    + case NAND_STATUS_1_3_CORRECTED:
    + mtd->ecc_stats.corrected++;
    + max_bitflips = 1;
    + break;
    + case NAND_STATUS_4_6_CORRECTED:
    + mtd->ecc_stats.corrected += 4;
    + /* rewrite recommended */
    + max_bitflips = chip->ecc.strength;
    + break;
    + case NAND_STATUS_7_8_CORRECTED:
    + mtd->ecc_stats.corrected += 7;
    + /* rewrite recommended */
    max_bitflips = chip->ecc.strength;
    + break;
    }

    ret = nand_read_data_op(chip, buf, mtd->writesize, false);
    @@ -239,13 +270,6 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
    if (feature[0] & ONFI_FEATURE_ON_DIE_ECC_EN)
    return MICRON_ON_DIE_MANDATORY;

    - /*
    - * Some Micron NANDs have an on-die ECC of 4/512, some other
    - * 8/512. We only support the former.
    - */
    - if (chip->ecc_strength_ds != 4)
    - return MICRON_ON_DIE_UNSUPPORTED;
    -
    return MICRON_ON_DIE_SUPPORTED;
    }

    @@ -275,9 +299,9 @@ static int micron_nand_init(struct nand_chip *chip)
    return -EINVAL;
    }

    - chip->ecc.bytes = 8;
    + chip->ecc.bytes = chip->ecc_strength_ds * 2;
    chip->ecc.size = 512;
    - chip->ecc.strength = 4;
    + chip->ecc.strength = chip->ecc_strength_ds;
    chip->ecc.algo = NAND_ECC_BCH;
    chip->ecc.read_page = micron_nand_read_page_on_die_ecc;
    chip->ecc.write_page = micron_nand_write_page_on_die_ecc;
    --
    2.17.1
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