From 78f43c53835076f342133e6d2d6e577d6ae06480 Mon Sep 17 00:00:00 2001 From: Pekon Gupta Date: Tue, 18 Mar 2014 18:56:44 +0530 Subject: [PATCH] mtd: nand: omap: ecc.correct: omap_elm_correct_data: fix erased-page detection for BCHx_HW ECC schemes 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 Signed-off-by: Brian Norris --- 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 4bf2f76d7d28..a6c979f3c61f 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; } } } -- 2.20.1