[PATCH v1 1/5] mtd: nand: omap: optimized chip->ecc.correct() for H/W ECC schemes
Pekon Gupta
pekon at ti.com
Mon Jul 15 10:55:48 EDT 2013
chip->ecc.correct() is used for detecting and correcting bit-flips during read
operations. In omap2-nand driver this is done usingt following functions:
- omap_correct_data(): for H/W based HAM1_ECC schemes
(Un-Touched in current patch)
- omap_elm_correct_data(): for H/W based BCHx_ECC scheme
Current implementation of this function is not scalable for newer ECC
schemes because:
- It depends on a specific byte-position in OOB area (reserved as 0x00)
to differentiates between programmed-pages and erased-pages.
This reserved byte-position cannot be accomodated in all ECC schemes.
- Current code is not scalable for future ECC schemes due to tweaks for
BCH4_ECC and BCH8_ECC at multiple places.
- It checks for bit-flips in Erased-pages using check_erased_page().
This is over-work, as sanity of Erased-page can be verified by just
comparing them to a pre-defined ECC-syndrome for all_0xFF data.
This patch optimizes omap_elm_correct_data() in following ways:
(1) Removes dependency on specific reserved-byte (0x00) in OOB area,
instead Erased-page is identified by matching calc_ecc with a
pre-defined ECC syndrome of all(0xFF) data
(2) merges common code for BCH4_ECC and BCH8_ECC for scalability.
(3) handles incorrect elm_error_location beyond data+oob buffer.
(4) removes check_erased_page(): Bit-flips in erased-page are handled
in same way as for programmed-page
Signed-off-by: Pekon Gupta <pekon at ti.com>
---
drivers/mtd/nand/omap2.c | 249 ++++++++++++++---------------------------------
1 file changed, 75 insertions(+), 174 deletions(-)
diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
index e9ef743..5321bdcc 100644
--- a/drivers/mtd/nand/omap2.c
+++ b/drivers/mtd/nand/omap2.c
@@ -176,6 +176,7 @@ struct omap_nand_info {
int gpmc_cs;
unsigned long phys_base;
unsigned long mem_size;
+ enum omap_ecc ecc_opt;
struct completion comp;
struct dma_chan *dma;
int gpmc_irq_fifo;
@@ -1307,219 +1308,118 @@ static int omap3_calculate_ecc_bch(struct mtd_info *mtd, const u_char *dat,
}
/**
- * erased_sector_bitflips - count bit flips
- * @data: data sector buffer
- * @oob: oob buffer
- * @info: omap_nand_info
- *
- * Check the bit flips in erased page falls below correctable level.
- * If falls below, report the page as erased with correctable bit
- * flip, else report as uncorrectable page.
- */
-static int erased_sector_bitflips(u_char *data, u_char *oob,
- struct omap_nand_info *info)
-{
- int flip_bits = 0, i;
-
- for (i = 0; i < info->nand.ecc.size; i++) {
- flip_bits += hweight8(~data[i]);
- if (flip_bits > info->nand.ecc.strength)
- return 0;
- }
-
- for (i = 0; i < info->nand.ecc.bytes - 1; i++) {
- flip_bits += hweight8(~oob[i]);
- if (flip_bits > info->nand.ecc.strength)
- return 0;
- }
-
- /*
- * Bit flips falls in correctable level.
- * Fill data area with 0xFF
- */
- if (flip_bits) {
- memset(data, 0xFF, info->nand.ecc.size);
- memset(oob, 0xFF, info->nand.ecc.bytes);
- }
-
- return flip_bits;
-}
-
-/**
* omap_elm_correct_data - corrects page data area in case error reported
* @mtd: MTD device structure
* @data: page data
* @read_ecc: ecc read from nand flash
- * @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.
- *
+ * @calc_ecc: ecc calculated after reading Data and OOB regions from flash
+ * As calc_ecc is calculated over both main & oob, so calc_ecc would be
+ * non-zero only in following cases:
+ * - bit-flips in data or oob region
+ * - erase page, where no ECC is written in OOB area
+ * However, erased_pages can be differentiated from corrupted pages
+ * by comparing the calculated ECC with pre-defined syndrome ECC_of_ALL(0xFF)
+ * Bit-flips in erased-pages would also be caught by comparing, calc_ecc
+ * with ECC_of_ALL(0xFF)
*/
static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
u_char *read_ecc, u_char *calc_ecc)
{
struct omap_nand_info *info = container_of(mtd, struct omap_nand_info,
mtd);
- int eccsteps = info->nand.ecc.steps;
- int i , j, stat = 0;
- int eccsize, eccflag, ecc_vector_size;
+ enum omap_ecc ecc_opt = info->ecc_opt;
+ struct nand_chip *chip = mtd->priv;
+ int eccsteps = chip->ecc.steps;
+ int eccsize = chip->ecc.size;
+ int eccbytes = chip->ecc.bytes;
+ int i , j, stat = 0, ret = 0, flag_read_ecc;
struct elm_errorvec err_vec[ERROR_VECTOR_MAX];
- u_char *ecc_vec = calc_ecc;
- u_char *spare_ecc = read_ecc;
- u_char *erased_ecc_vec;
- enum bch_ecc type;
+ u_char *ecc;
bool is_error_reported = false;
+ u32 bit_pos, byte_pos, error_max, pos;
/* Initialize elm error vector to zero */
memset(err_vec, 0, sizeof(err_vec));
- 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;
- }
-
- ecc_vector_size = info->nand.ecc.bytes;
-
- /*
- * Remove extra byte padding for BCH8 RBL
- * compatibility and erased page handling
- */
- eccsize = ecc_vector_size - 1;
-
for (i = 0; i < eccsteps ; i++) {
- eccflag = 0; /* initialize eccflag */
-
- /*
- * Check any error reported,
- * In case of error, non zero ecc reported.
- */
-
- for (j = 0; (j < eccsize); j++) {
- if (calc_ecc[j] != 0) {
- eccflag = 1; /* non zero ecc, error present */
+ flag_read_ecc = 0;
+ ecc = calc_ecc + (i * eccbytes);
+ /* check calc_ecc */
+ for (j = 0; j < eccbytes; j++) {
+ if (*(ecc + j) != 0x00) {
+ flag_read_ecc = 1;
break;
}
}
-
- 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[eccsize]) >= threshold) {
- /*
- * Update elm error vector as
- * data area is programmed
- */
- 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, eccsize)) {
- bitflip_count = erased_sector_bitflips(
- buf, read_ecc, info);
-
- if (bitflip_count)
- stat += bitflip_count;
- else
- return -EINVAL;
- }
+ /* check if its a erased-page */
+ if (flag_read_ecc) {
+ switch (ecc_opt) {
+ case OMAP_ECC_BCH8_CODE_HW:
+ if (memcmp(ecc, bch8_vector, eccbytes))
+ err_vec[i].error_reported = true;
+ break;
+ case OMAP_ECC_BCH4_CODE_HW:
+ if (memcmp(ecc, bch4_vector, eccbytes))
+ err_vec[i].error_reported = true;
+ break;
+ default:
+ pr_err("%s: invalid configuration",
+ DRIVER_NAME);
+ return -EINVAL;
}
}
-
- /* Update the ecc vector */
- calc_ecc += ecc_vector_size;
- read_ecc += ecc_vector_size;
+ /* page definitely has bit-flips */
+ if (err_vec[i].error_reported)
+ is_error_reported = true;
}
- /* Check if any error reported */
if (!is_error_reported)
return 0;
+ /* detect bit-flips using ELM module */
+ elm_decode_bch_error_page(info->elm_dev, calc_ecc, err_vec);
- /* Decode BCH error using ELM module */
- elm_decode_bch_error_page(info->elm_dev, ecc_vec, err_vec);
-
+ /* correct bit-flip */
for (i = 0; i < eccsteps; i++) {
- if (err_vec[i].error_reported) {
+ if (err_vec[i].error_uncorrectable) {
+ ret = -EBADMSG;
+ } else if (err_vec[i].error_reported) {
for (j = 0; j < err_vec[i].error_count; j++) {
- u32 bit_pos, byte_pos, error_max, pos;
-
- if (type == BCH8_ECC)
- error_max = BCH8_ECC_MAX;
- else
- error_max = BCH4_ECC_MAX;
-
- if (info->nand.ecc.strength == BCH8_MAX_ERROR)
- pos = err_vec[i].error_loc[j];
- else
+ switch (ecc_opt) {
+ case OMAP_ECC_BCH4_CODE_HW:
+ error_max = SECTOR_BYTES +
+ (eccbytes - 1);
/* Add 4 to take care 4 bit padding */
pos = err_vec[i].error_loc[j] +
- BCH4_BIT_PAD;
-
- /* Calculate bit position of error */
+ BCH4_BIT_PAD;
+ break;
+ case OMAP_ECC_BCH8_CODE_HW:
+ error_max = SECTOR_BYTES +
+ (eccbytes - 1);
+ pos = err_vec[i].error_loc[j];
+ break;
+ default:
+ return -EINVAL;
+ }
+ /* Calculate bit & byte bit-flip position */
bit_pos = pos % 8;
-
- /* Calculate byte position of error */
- byte_pos = (error_max - pos - 1) / 8;
-
- if (pos < error_max) {
- if (byte_pos < 512)
- data[byte_pos] ^= 1 << bit_pos;
- else
- spare_ecc[byte_pos - 512] ^=
+ byte_pos = error_max - (pos / 8) - 1;
+ if (byte_pos < SECTOR_BYTES)
+ data[byte_pos] ^= 1 << bit_pos;
+ else if (byte_pos < error_max)
+ read_ecc[byte_pos - SECTOR_BYTES] ^=
1 << bit_pos;
- }
- /* else, not interested to correct ecc */
+ else
+ ret = -EBADMSG;
}
}
-
/* Update number of correctable errors */
stat += err_vec[i].error_count;
-
/* Update page data with sector size */
- data += info->nand.ecc.size;
- spare_ecc += ecc_vector_size;
+ data += eccsize;
+ read_ecc += eccbytes;
}
- for (i = 0; i < eccsteps; i++)
- /* Return error if uncorrectable error present */
- if (err_vec[i].error_uncorrectable)
- return -EINVAL;
-
- return stat;
+ return (ret < 0) ? ret : stat;
}
/**
@@ -1677,13 +1577,14 @@ static int omap_nand_probe(struct platform_device *pdev)
info->pdev = pdev;
info->gpmc_cs = pdata->cs;
info->reg = pdata->reg;
+ info->ecc_opt = pdata->ecc_opt;
info->nand.options = NAND_BUSWIDTH_AUTO;
info->nand.options |= NAND_SKIP_BBTSCAN;
+ info->nand.ecc.priv = NULL;
#ifdef CONFIG_MTD_NAND_OMAP_BCH
info->of_node = pdata->of_node;
#endif
- info->nand.ecc.priv = NULL;
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (res == NULL) {
--
1.8.1
More information about the linux-mtd
mailing list