[RFC 22/47] mtd: nand: stm_nand_bch: check erased page for zeros

Lee Jones
2014-03-25T08:21:22Z

Detect an erased page, tolerating and correcting up to a specified number
of bits at '0'. Downgrade uncorrectable ECC error for an erased page,
tolerating 'sectors_per_page' bits at '0'.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
---
drivers/mtd/nand/stm_nand_bch.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/drivers/mtd/nand/stm_nand_bch.c b/drivers/mtd/nand/stm_nand_bch.c
index 2042cdd..7874d85 100644
--- a/drivers/mtd/nand/stm_nand_bch.c
+++ b/drivers/mtd/nand/stm_nand_bch.c
@@ -319,6 +319,33 @@ static uint8_t bch_erase_block(struct nandi_controller *nandi,
}

/*
+ * Detect an erased page, tolerating and correcting up to a specified number of
+ * bits at '0'. (For many devices, it is now deemed within spec for an erased
+ * page to include a number of bits at '0', either as a result of read-disturb
+ * behaviour or 'stuck-at-zero' failures.) Returns the number of corrected
+ * bits, or a '-1' if we have exceeded the maximum number of bits at '0' (likely
+ * to be a genuine uncorrectable ECC error). In the latter case, the data must
+ * be returned unmodified, in accordance with the MTD API.
+ */
+static int check_erased_page(uint8_t *data, uint32_t page_size, int max_zeros)
+{
+ uint8_t *b = data;
+ int zeros = 0;
+ int i;
+
+ for (i = 0; i < page_size; i++) {
+ zeros += hweight8(~*b++);
+ if (zeros > max_zeros)
+ return -1;
+ }
+
+ if (zeros)
+ memset(data, 0xff, page_size);
+
+ return zeros;
+}
+
+/*
* Initialisation
*/
static int bch_check_compatibility(struct nandi_controller *nandi,
--
1.8.3.2