[PATCH] mtd: gpmi: Deal with bitflips in erased regions
Stefan Christ
s.christ at phytec.de
Tue Mar 15 01:35:37 PDT 2016
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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