[PATCH] mtd: gpmi: Deal with bitflips in erased regions
Stefan Christ
s.christ at phytec.de
Mon Apr 11 04:18:52 PDT 2016
Hi,
*ping for my last email. Again this is a real issue for deployed devices and
should be fixed in the mainline kernel.
I hope that the patch author maybe step up and vote that his patch gets
accepted into mainline, too.
The original patch disccusion is
http://lists.infradead.org/pipermail/linux-mtd/2014-January/051356.html
There seems to be no issues left with this patch.
Mit freundlichen Grüßen / Kind regards,
Stefan Christ
On Tue, Mar 15, 2016 at 09:35:37AM +0100, Stefan Christ wrote:
> From: Elie De Brauwer <eliedebrauwer at gmail.com>
>
> The BCH block typically used with a GPMI block on an i.MX28/i.MX6 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 problem was also observed
> when using SLC NAND devices.
>
> This patch configures the BCH block to mark a block as 'erased' if
> not too much bitflips are found (by setting the erase threshold). A
> consequence of this is that whenever an erased page is read, the
> number of bitflips will be 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>
> Acked-by: Huang Shijie <b32955 at freescale.com>
> ---
> Hi,
>
> I'm reposting this patch, because it's still not in the mainline kernel tree.
> It was taken from
>
> http://lists.infradead.org/pipermail/linux-mtd/2014-January/051357.html
> [PATCH v7] mtd: gpmi: Deal with bitflips in erased regions
>
> The patch fixes the UBI corrupted empty space problem:
>
> UBIFS error (pid 74): ubifs_scan: corrupt empty space at LEB 3059:72260
> UBIFS error (pid 74): ubifs_scanned_corruption: corruption at LEB 3059:72260
> UBIFS error (pid 74): ubifs_scanned_corruption: first 8192 bytes from LEB 3059:72260
> UBIFS error (pid 74): ubifs_scan: LEB 3059 scanning failed
>
> which occurs in real systems sometimes.
>
> I've tested the patch. You can add my
>
> Tested-by: Stefan Christ <s.christ at phytec.de>
>
> Mit freundlichen Grüßen / Kind regards,
> Stefan Christ
>
> ---
> drivers/mtd/nand/gpmi-nand/bch-regs.h | 1 +
> drivers/mtd/nand/gpmi-nand/gpmi-lib.c | 9 +++++++
> drivers/mtd/nand/gpmi-nand/gpmi-nand.c | 43 +++++++++++++++++++++++++++++++---
> 3 files changed, 50 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/mtd/nand/gpmi-nand/bch-regs.h b/drivers/mtd/nand/gpmi-nand/bch-regs.h
> index 05bb91f..88cc89d 100644
> --- a/drivers/mtd/nand/gpmi-nand/bch-regs.h
> +++ b/drivers/mtd/nand/gpmi-nand/bch-regs.h
> @@ -31,6 +31,7 @@
>
> #define HW_BCH_STATUS0 0x00000010
> #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 0f68a99..a724dcb 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> @@ -256,6 +256,7 @@ int bch_set_geometry(struct gpmi_nand_data *this)
> unsigned int ecc_strength;
> unsigned int page_size;
> unsigned int gf_len;
> + unsigned int erase_threshold;
> int ret;
>
> if (common_nfc_set_geometry(this))
> @@ -298,6 +299,14 @@ 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. */
> + erase_threshold = gf_len / 2;
> + if (erase_threshold > bch_geo->ecc_strength)
> + erase_threshold = bch_geo->ecc_strength;
> +
> + writel(erase_threshold & BM_BCH_MODE_ERASE_THRESHOLD_MASK,
> + r->bch_regs + HW_BCH_MODE);
> +
> /* Set *all* chip selects to use layout 0. */
> writel(0, r->bch_regs + HW_BCH_LAYOUTSELECT);
>
> diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> index 235ddcb..ba852e8 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> @@ -991,6 +991,30 @@ 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)
> {
> @@ -1002,6 +1026,7 @@ 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;
>
> @@ -1036,15 +1061,27 @@ 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);
> +
> + /*
> + * The number of bitflips are either counted in software
> + * in case of an erased chunk or otherwise reported by
> + * the BCH block.
> + */
> + if (*status == STATUS_ERASED)
> + flips = erased_sector_bitflips(payload_virt, i,
> + nfc_geo);
> + else
> + flips = *status;
> +
> + mtd->ecc_stats.corrected += flips;
> + max_bitflips = max_t(unsigned int, max_bitflips, flips);
> }
>
> if (oob_required) {
> --
> 1.9.1
>
>
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