[PATCH v9 3/5] mtd: nand: omap: ecc.correct: omap_elm_correct_data: fix erased-page detection for BCHx_HW ECC schemes
Pekon Gupta
pekon at ti.com
Tue Mar 18 09:26:44 EDT 2014
As erased-pages do not have ECC stored in their OOB area, so they need to be
seperated out from programmed-pages, before doing BCH ECC correction.
In current implementation of omap_elm_correct_data() which does ECC correction
for BCHx ECC schemes, this erased-pages are detected based on specific marker
byte (reserved as 0x00) in ecc-layout.
However, this approach has some limitation like;
1) All ecc-scheme layouts do not have such Reserved byte marker to
differentiate between erased-page v/s programmed-page. Thus this is a
customized solution.
2) Reserved marker byte can itself be subjected to bit-flips causing
erased-page to be misunderstood as programmed-page.
This patch removes dependency on any marker byte in ecc-layout, instead it
compares calc_ecc[] with pattern of ECC-of-all(0xff). This implicitely
means that both 'data + oob == all(0xff).
Signed-off-by: Pekon Gupta <pekon at ti.com>
---
drivers/mtd/nand/omap2.c | 85 +++++++++++++++++++-----------------------------
1 file changed, 33 insertions(+), 52 deletions(-)
diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
index 4bf2f76d..a6c979f 100644
--- a/drivers/mtd/nand/omap2.c
+++ b/drivers/mtd/nand/omap2.c
@@ -1338,21 +1338,8 @@ static int erased_sector_bitflips(u_char *data, u_char *oob,
* @calc_ecc: ecc read from HW ECC registers
*
* Calculated ecc vector reported as zero in case of non-error pages.
- * In case of error/erased pages non-zero error vector is reported.
- * In case of non-zero ecc vector, check read_ecc at fixed offset
- * (x = 13/7 in case of BCH8/4 == 0) to find page programmed or not.
- * To handle bit flips in this data, count the number of 0's in
- * read_ecc[x] and check if it greater than 4. If it is less, it is
- * programmed page, else erased page.
- *
- * 1. If page is erased, check with standard ecc vector (ecc vector
- * for erased page to find any bit flip). If check fails, bit flip
- * is present in erased page. Count the bit flips in erased page and
- * if it falls under correctable level, report page with 0xFF and
- * update the correctable bit information.
- * 2. If error is reported on programmed page, update elm error
- * vector and correct the page with ELM error correction routine.
- *
+ * In case of non-zero ecc vector, first filter out erased-pages, and
+ * then process data via ELM to detect bit-flips.
*/
static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
u_char *read_ecc, u_char *calc_ecc)
@@ -1367,6 +1354,8 @@ static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
u_char *ecc_vec = calc_ecc;
u_char *spare_ecc = read_ecc;
u_char *erased_ecc_vec;
+ u_char *buf;
+ int bitflip_count;
enum bch_ecc type;
bool is_error_reported = false;
@@ -1374,10 +1363,12 @@ static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
case OMAP_ECC_BCH4_CODE_HW:
/* omit 7th ECC byte reserved for ROM code compatibility */
actual_eccbytes = ecc->bytes - 1;
+ erased_ecc_vec = bch4_vector;
break;
case OMAP_ECC_BCH8_CODE_HW:
/* omit 14th ECC byte reserved for ROM code compatibility */
actual_eccbytes = ecc->bytes - 1;
+ erased_ecc_vec = bch8_vector;
break;
default:
pr_err("invalid driver configuration\n");
@@ -1389,10 +1380,8 @@ static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
if (info->nand.ecc.strength == BCH8_MAX_ERROR) {
type = BCH8_ECC;
- erased_ecc_vec = bch8_vector;
} else {
type = BCH4_ECC;
- erased_ecc_vec = bch4_vector;
}
for (i = 0; i < eccsteps ; i++) {
@@ -1410,44 +1399,36 @@ static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
}
if (eccflag == 1) {
- /*
- * Set threshold to minimum of 4, half of ecc.strength/2
- * to allow max bit flip in byte to 4
- */
- unsigned int threshold = min_t(unsigned int, 4,
- info->nand.ecc.strength / 2);
-
- /*
- * Check data area is programmed by counting
- * number of 0's at fixed offset in spare area.
- * Checking count of 0's against threshold.
- * In case programmed page expects at least threshold
- * zeros in byte.
- * If zeros are less than threshold for programmed page/
- * zeros are more than threshold erased page, either
- * case page reported as uncorrectable.
- */
- if (hweight8(~read_ecc[actual_eccbytes]) >= threshold) {
+ if (memcmp(calc_ecc, erased_ecc_vec,
+ actual_eccbytes) == 0) {
/*
- * Update elm error vector as
- * data area is programmed
+ * calc_ecc[] matches pattern for ECC(all 0xff)
+ * so this is definitely an erased-page
*/
- err_vec[i].error_reported = true;
- is_error_reported = true;
} else {
- /* Error reported in erased page */
- int bitflip_count;
- u_char *buf = &data[info->nand.ecc.size * i];
-
- if (memcmp(calc_ecc, erased_ecc_vec,
- actual_eccbytes)) {
- bitflip_count = erased_sector_bitflips(
- buf, read_ecc, info);
-
- if (bitflip_count)
- stat += bitflip_count;
- else
- return -EINVAL;
+ buf = &data[info->nand.ecc.size * i];
+ /*
+ * count number of 0-bits in read_buf.
+ * This check can be removed once a similar
+ * check is introduced in generic NAND driver
+ */
+ bitflip_count = erased_sector_bitflips(
+ buf, read_ecc, info);
+ if (bitflip_count) {
+ /*
+ * number of 0-bits within ECC limits
+ * So this may be an erased-page
+ */
+ stat += bitflip_count;
+ } else {
+ /*
+ * Too many 0-bits. It may be a
+ * - programmed-page, OR
+ * - erased-page with many bit-flips
+ * So this page requires check by ELM
+ */
+ err_vec[i].error_reported = true;
+ is_error_reported = true;
}
}
}
--
1.8.5.1.163.gd7aced9
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