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mtd: nand: omap: ecc.correct: omap_elm_correct_data: fix erased-page detection for BCHx_HW ECC schemes

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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@ti.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
This commit is contained in:
Pekon Gupta 2014-03-18 18:56:44 +05:30 committed by Brian Norris
parent de0a4d69e6
commit 78f43c5383
1 changed files with 33 additions and 52 deletions
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85
drivers/mtd/nand/omap2.c
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@ -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;
}
}
}