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[v4,1/4] mtd: nand: omap: optimized chip->ecc.correct() for H/W ECC schemes

Message ID 1385374141-10934-2-git-send-email-pekon@ti.com
State New, archived
Headers show

Commit Message

pekon gupta Nov. 25, 2013, 10:08 a.m. UTC
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@ti.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
---
 drivers/mtd/nand/omap2.c | 247 ++++++++++++++---------------------------------
 1 file changed, 74 insertions(+), 173 deletions(-)
diff mbox

Patch

diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
index f777250..2f49ff3 100644
--- a/drivers/mtd/nand/omap2.c
+++ b/drivers/mtd/nand/omap2.c
@@ -160,6 +160,7 @@  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;
@@ -1291,219 +1292,118 @@  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;
 }
 
 /**
@@ -1656,6 +1556,7 @@  static int omap_nand_probe(struct platform_device *pdev)
 	info->gpmc_cs		= pdata->cs;
 	info->reg		= pdata->reg;
 	info->of_node		= pdata->of_node;
+	info->ecc_opt		= pdata->ecc_opt;
 	mtd			= &info->mtd;
 	mtd->priv		= &info->nand;
 	mtd->name		= dev_name(&pdev->dev);