From ceb324a2914487aa517a6c70a06a20b5e3438fda Mon Sep 17 00:00:00 2001 From: Peng Fan Date: Fri, 6 May 2016 12:13:38 +0800 Subject: [PATCH] MLK-12693-1 nand: mxs: fix the bitflips for erased page when uncorrectable error This patch is porting from linux: http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/commit/?h=imx_4.1.15_1.0.0_ga&id=3d42fcece496224fde59f9343763fb2dfc5b0768 " We may meet the bitflips in reading an erased page(contains all 0xFF), this may causes the UBIFS corrupt, please see the log from Elie: ----------------------------------------------------------------- [ 3.831323] UBI warning: ubi_io_read: error -74 (ECC error) while reading 16384 bytes from PEB 443:245760, read only 16384 bytes, retry [ 3.845026] UBI warning: ubi_io_read: error -74 (ECC error) while reading 16384 bytes from PEB 443:245760, read only 16384 bytes, retry [ 3.858710] UBI warning: ubi_io_read: error -74 (ECC error) while reading 16384 bytes from PEB 443:245760, read only 16384 bytes, retry [ 3.872408] UBI error: ubi_io_read: error -74 (ECC error) while reading 16384 bytes from PEB 443:245760, read 16384 bytes ... [ 4.011529] UBIFS error (pid 36): ubifs_recover_leb: corrupt empty space LEB 27:237568, corruption starts at 9815 [ 4.021897] UBIFS error (pid 36): ubifs_scanned_corruption: corruption at LEB 27:247383 [ 4.030000] UBIFS error (pid 36): ubifs_scanned_corruption: first 6569 bytes from LEB 27:247383 ----------------------------------------------------------------- This patch does a check for the uncorrectable failure in the following steps: [0] set the threshold. The threshold is set based on the truth: "A single 0 bit will lead to gf_len(13 or 14) bits 0 after the BCH do the ECC." For the sake of safe, we will set the threshold with half the gf_len, and do not make it bigger the ECC strength. [1] count the bitflips of the current ECC chunk, assume it is N. [2] if the (N <= threshold) is true, we continue to read out the page with ECC disabled. and we count the bitflips again, assume it is N2. (We read out the whole page, not just a chunk, this makes the check more strictly, and make the code more simple.) [3] if the (N2 <= threshold) is true again, we can regard this is a erased page. This is because a real erased page is full of 0xFF(maybe also has several bitflips), while a page contains the 0xFF data will definitely has many bitflips in the ECC parity areas. [4] if the [3] fails, we can regard this is a page filled with the '0xFF' data. " Signed-off-by: Peng Fan --- drivers/mtd/nand/mxs_nand.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+) diff --git a/drivers/mtd/nand/mxs_nand.c b/drivers/mtd/nand/mxs_nand.c index 2d75124..7cd5fd0 100644 --- a/drivers/mtd/nand/mxs_nand.c +++ b/drivers/mtd/nand/mxs_nand.c @@ -640,6 +640,45 @@ static uint8_t mxs_nand_read_byte(struct mtd_info *mtd) return buf; } +static bool mxs_nand_erased_page(struct mtd_info *mtd, struct nand_chip *nand, + uint8_t *buf, int chunk, int page) +{ + int gf_len = galois_field; + unsigned int flip_bits = 0, flip_bits_noecc = 0; + unsigned int threshold; + unsigned int ecc_chunkn_size = MXS_NAND_CHUNK_DATA_CHUNK_SIZE; + unsigned int base = ecc_chunkn_size * chunk; + uint32_t *dma_buf = (uint32_t *)buf; + int i; + + threshold = gf_len / 2; + if (threshold > ecc_strength) + threshold = ecc_strength; + + for (i = 0; i < ecc_chunkn_size; i++) { + flip_bits += hweight8(~buf[base + i]); + if (flip_bits > threshold) + return false; + } + + nand->cmdfunc(mtd, NAND_CMD_READ0, 0, page); + nand->read_buf(mtd, buf, mtd->writesize); + + for (i = 0; i < mtd->writesize / 4; i++) { + flip_bits_noecc += hweight32(~dma_buf[i]); + if (flip_bits_noecc > threshold) + return false; + } + + mtd->ecc_stats.corrected += flip_bits; + + memset(buf, 0xff, mtd->writesize); + + printf("The page(%d) is an erased page(%d,%d,%d,%d).\n", page, chunk, threshold, flip_bits, flip_bits_noecc); + + return true; +} + /* * Read a page from NAND. */ @@ -742,6 +781,8 @@ static int mxs_nand_ecc_read_page(struct mtd_info *mtd, struct nand_chip *nand, goto rtn; } + mxs_nand_return_dma_descs(nand_info); + /* Invalidate caches */ mxs_nand_inval_data_buf(nand_info); @@ -758,6 +799,9 @@ static int mxs_nand_ecc_read_page(struct mtd_info *mtd, struct nand_chip *nand, continue; if (status[i] == 0xfe) { + if (mxs_nand_erased_page(mtd, nand, + nand_info->data_buf, i, page)) + break; failed++; continue; } -- 1.9.1