[PATCH v2] mtd: gpmi: Deal with bitflips in erased regions regions
Huang Shijie
b32955 at freescale.com
Sun Dec 15 23:30:41 EST 2013
On Sun, Dec 15, 2013 at 07:44:21PM +0100, Elie De Brauwer wrote:
> The BCH block typically used with a i.MX28 and GPMI block is only
> able to correct bitflips on data actually streamed through the block.
> When erasing a block the data does not stream through the BCH block
> and therefore no ECC data is written to the NAND chip. This causes
> gpmi_ecc_read_page to return failure as soon as a single non-1-bit is
> found in an erased page. Typically causing problems at higher levels
> (ubifs corrupted empty space warnings).
>
> This patch configures the BCH block to mark a block as 'erased' if
> no more than ecc_strength bitflips are found. Next HW_BCH_STATUS0:ALLONES
> is used to check if the data read were all ones. If this was not
> the case a slow path is entered where bitflips are counted and
> corrected in software, allowing the upper layers to take proper actions.
>
> Signed-off-by: Elie De Brauwer <eliedebrauwer at gmail.com>
> Acked-by: Peter Korsgaard <peter at korsgaard.com>
> ---
> drivers/mtd/nand/gpmi-nand/bch-regs.h | 2 ++
> drivers/mtd/nand/gpmi-nand/gpmi-lib.c | 17 +++++++++++++
> drivers/mtd/nand/gpmi-nand/gpmi-nand.c | 43 +++++++++++++++++++++++++++++---
> drivers/mtd/nand/gpmi-nand/gpmi-nand.h | 1 +
> 4 files changed, 60 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mtd/nand/gpmi-nand/bch-regs.h b/drivers/mtd/nand/gpmi-nand/bch-regs.h
> index 588f537..a30502f 100644
> --- a/drivers/mtd/nand/gpmi-nand/bch-regs.h
> +++ b/drivers/mtd/nand/gpmi-nand/bch-regs.h
> @@ -30,7 +30,9 @@
> #define BM_BCH_CTRL_COMPLETE_IRQ (1 << 0)
>
> #define HW_BCH_STATUS0 0x00000010
> +#define BM_BCH_STATUS0_ALLONES_MASK (1 << 4)
> #define HW_BCH_MODE 0x00000020
> +#define BM_BCH_MODE_ERASE_THRESHOLD_MASK 0xff
> #define HW_BCH_ENCODEPTR 0x00000030
> #define HW_BCH_DATAPTR 0x00000040
> #define HW_BCH_METAPTR 0x00000050
> diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> index aaced29..4551a38 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> @@ -286,6 +286,13 @@ int bch_set_geometry(struct gpmi_nand_data *this)
> | BF_BCH_FLASH0LAYOUT1_DATAN_SIZE(block_size, this),
> r->bch_regs + HW_BCH_FLASH0LAYOUT1);
>
> + /*
> + * Set the tolerance for bitflips when reading erased blocks
> + * equal to the ecc_strength.
> + */
Please also add the following comment :
"We even detect the bitflips for SLC nand."
> + writel(bch_geo->ecc_strength & BM_BCH_MODE_ERASE_THRESHOLD_MASK,
> + r->bch_regs + HW_BCH_MODE);
> +
After discuss with the IC owner, we could set the bch_geo->gf_len here.
The bch_geo->gf_len is 13 or 14 now.
For the sake of safe, I suggest to set (bch_geo->gf_len / 2) for the ERASE_THRESHOLD.
I think this value is enough for us.
> /* Set *all* chip selects to use layout 0. */
> writel(0, r->bch_regs + HW_BCH_LAYOUTSELECT);
>
> @@ -1094,6 +1101,16 @@ int gpmi_is_ready(struct gpmi_nand_data *this, unsigned chip)
> return reg & mask;
> }
>
> +/* Returns 1 if the last transaction consisted only out of ones. */
> +int gpmi_allones(struct gpmi_nand_data *this)
> +{
> + struct resources *r = &this->resources;
> + uint32_t reg = readl(r->gpmi_regs + HW_BCH_STATUS0);
please add a empty line here.
> + if (reg & BM_BCH_STATUS0_ALLONES_MASK)
> + return 1;
> + return 0;
We can simplify the code to:
return reg & BM_BCH_STATUS0_ALLONES_MASK;
> +}
> +
> static inline void set_dma_type(struct gpmi_nand_data *this,
> enum dma_ops_type type)
> {
> diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> index dabbc14..82eac9b 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> @@ -1012,6 +1012,30 @@ static void block_mark_swapping(struct gpmi_nand_data *this,
> p[1] = (p[1] & mask) | (from_oob >> (8 - bit));
> }
>
> +/*
> + * Count the number of 0 bits in a supposed to be
> + * erased region and correct them. Return the number
> + * of bitflips or zero when the region was correct.
> + */
> +static unsigned int erased_sector_bitflips(unsigned char *data,
> + unsigned int chunk,
> + struct bch_geometry *geo)
> +{
> + unsigned int flip_bits = 0;
> + int i;
> + int base = geo->ecc_chunk_size * chunk;
> +
> + /* Count bitflips */
> + for (i = 0; i < geo->ecc_chunk_size; i++)
> + flip_bits += hweight8(~data[base + i]);
> +
> + /* Correct bitflips by 0xFF'ing this chunk. */
> + if (flip_bits)
> + memset(&data[base], 0xFF, geo->ecc_chunk_size);
> +
> + return flip_bits;
> +}
> +
> static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> uint8_t *buf, int oob_required, int page)
> {
> @@ -1023,6 +1047,7 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> dma_addr_t auxiliary_phys;
> unsigned int i;
> unsigned char *status;
> + unsigned int flips;
> unsigned int max_bitflips = 0;
> int ret;
>
> @@ -1057,15 +1082,27 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> status = auxiliary_virt + nfc_geo->auxiliary_status_offset;
>
> for (i = 0; i < nfc_geo->ecc_chunk_count; i++, status++) {
> - if ((*status == STATUS_GOOD) || (*status == STATUS_ERASED))
> + if (*status == STATUS_GOOD)
> continue;
>
> if (*status == STATUS_UNCORRECTABLE) {
> mtd->ecc_stats.failed++;
> continue;
> }
> - mtd->ecc_stats.corrected += *status;
> - max_bitflips = max_t(unsigned int, max_bitflips, *status);
> +
> + if (*status == STATUS_ERASED)
> + if (gpmi_allones(this))
> + continue;
> + else
> + /* Erased block with bitflips. */
> + flips = erased_sector_bitflips(payload_virt, i,
> + nfc_geo);
> + else
> + /* BCH block corrected some errors for us. */
> + flips = *status;
Please read the Documentation/CodeingStyle.
The code should like this:
........................................................
if (*status == STATUS_ERASED) {
if (gpmi_allones(this))
continue;
else
/* Erased block with bitflips. */
flips = erased_sector_bitflips(payload_virt, i,
nfc_geo);
} else {
/* BCH block corrected some errors for us. */
flips = *status;
}
........................................................
thanks
Huang Shijie
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