[PATCH/RFC v2 2/3] mtd: nand: add software BCH ECC support
Ivan Djelic
ivan.djelic at parrot.com
Mon Feb 7 09:09:31 EST 2011
This patch adds software BCH ECC support to mtd, in order to handle recent
NAND device ecc requirements (4 bits or more).
It does so by adding a new ecc mode (NAND_ECC_SOFT_BCH) for use by board
drivers, and a new Kconfig option to enable BCH support. It relies on the
generic BCH library introduced in a previous patch.
When a board driver uses mode NAND_ECC_SOFT_BCH, it should also set fields
chip->ecc.size and chip->ecc.bytes to select BCH ecc data size and required
error correction capability. See nand_bch_init() documentation for details.
It has been tested on the following platforms using mtd-utils, UBI and
UBIFS: x86 (with nandsim), arm926ejs.
Signed-off-by: Ivan Djelic <ivan.djelic at parrot.com>
---
v2 changelog:
- do not handle small page devices as we do not provide ecc layouts for them
drivers/mtd/nand/Kconfig | 15 +++
drivers/mtd/nand/Makefile | 1 +
drivers/mtd/nand/nand_base.c | 40 +++++++-
drivers/mtd/nand/nand_bch.c | 245 ++++++++++++++++++++++++++++++++++++++++++
include/linux/mtd/nand.h | 3 +
include/linux/mtd/nand_bch.h | 74 +++++++++++++
6 files changed, 377 insertions(+), 1 deletions(-)
create mode 100644 drivers/mtd/nand/nand_bch.c
create mode 100644 include/linux/mtd/nand_bch.h
diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
index c895922..78205ac 100644
--- a/drivers/mtd/nand/Kconfig
+++ b/drivers/mtd/nand/Kconfig
@@ -31,6 +31,21 @@ config MTD_NAND_VERIFY_WRITE
device thinks the write was successful, a bit could have been
flipped accidentally due to device wear or something else.
+config MTD_NAND_BCH
+ tristate
+ select BCH
+ depends on MTD_NAND_ECC_BCH
+ default MTD_NAND
+
+config MTD_NAND_ECC_BCH
+ bool "Support software BCH ECC"
+ default n
+ help
+ This enables support for software BCH error correction. Binary BCH
+ codes are more powerful and cpu intensive than traditional Hamming
+ ECC codes. They are used with NAND devices requiring more than 1 bit
+ of error correction.
+
config MTD_SM_COMMON
tristate
default n
diff --git a/drivers/mtd/nand/Makefile b/drivers/mtd/nand/Makefile
index 8ad6fae..5745d83 100644
--- a/drivers/mtd/nand/Makefile
+++ b/drivers/mtd/nand/Makefile
@@ -4,6 +4,7 @@
obj-$(CONFIG_MTD_NAND) += nand.o
obj-$(CONFIG_MTD_NAND_ECC) += nand_ecc.o
+obj-$(CONFIG_MTD_NAND_BCH) += nand_bch.o
obj-$(CONFIG_MTD_NAND_IDS) += nand_ids.o
obj-$(CONFIG_MTD_SM_COMMON) += sm_common.o
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 4915067..48ef5e1 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -42,6 +42,7 @@
#include <linux/mtd/mtd.h>
#include <linux/mtd/nand.h>
#include <linux/mtd/nand_ecc.h>
+#include <linux/mtd/nand_bch.h>
#include <linux/interrupt.h>
#include <linux/bitops.h>
#include <linux/leds.h>
@@ -3248,7 +3249,7 @@ int nand_scan_tail(struct mtd_info *mtd)
/*
* If no default placement scheme is given, select an appropriate one
*/
- if (!chip->ecc.layout) {
+ if (!chip->ecc.layout && (chip->ecc.mode != NAND_ECC_SOFT_BCH)) {
switch (mtd->oobsize) {
case 8:
chip->ecc.layout = &nand_oob_8;
@@ -3351,6 +3352,40 @@ int nand_scan_tail(struct mtd_info *mtd)
chip->ecc.bytes = 3;
break;
+ case NAND_ECC_SOFT_BCH:
+ if (!mtd_nand_has_bch()) {
+ printk(KERN_WARNING "CONFIG_MTD_ECC_BCH not enabled\n");
+ BUG();
+ }
+ chip->ecc.calculate = nand_bch_calculate_ecc;
+ chip->ecc.correct = nand_bch_correct_data;
+ chip->ecc.read_page = nand_read_page_swecc;
+ chip->ecc.read_subpage = nand_read_subpage;
+ chip->ecc.write_page = nand_write_page_swecc;
+ chip->ecc.read_page_raw = nand_read_page_raw;
+ chip->ecc.write_page_raw = nand_write_page_raw;
+ chip->ecc.read_oob = nand_read_oob_std;
+ chip->ecc.write_oob = nand_write_oob_std;
+ /*
+ * Board driver should supply ecc.size and ecc.bytes values to
+ * select how many bits are correctable; see nand_bch_init()
+ * for details.
+ * Otherwise, default to 4 bits for large page devices
+ */
+ if (!chip->ecc.size && (mtd->oobsize >= 64)) {
+ chip->ecc.size = 512;
+ chip->ecc.bytes = 7;
+ }
+ chip->ecc.priv = nand_bch_init(mtd,
+ chip->ecc.size,
+ chip->ecc.bytes,
+ &chip->ecc.layout);
+ if (!chip->ecc.priv) {
+ printk(KERN_WARNING "BCH ECC initialization failed!\n");
+ BUG();
+ }
+ break;
+
case NAND_ECC_NONE:
printk(KERN_WARNING "NAND_ECC_NONE selected by board driver. "
"This is not recommended !!\n");
@@ -3501,6 +3536,9 @@ void nand_release(struct mtd_info *mtd)
{
struct nand_chip *chip = mtd->priv;
+ if (chip->ecc.mode == NAND_ECC_SOFT_BCH)
+ nand_bch_free((struct nand_bch_control *)chip->ecc.priv);
+
#ifdef CONFIG_MTD_PARTITIONS
/* Deregister partitions */
del_mtd_partitions(mtd);
diff --git a/drivers/mtd/nand/nand_bch.c b/drivers/mtd/nand/nand_bch.c
new file mode 100644
index 0000000..5e5f8df
--- /dev/null
+++ b/drivers/mtd/nand/nand_bch.c
@@ -0,0 +1,245 @@
+/*
+ * drivers/mtd/nand/nand_bch.c
+ *
+ * This file provides ECC correction for more than 1 bit per block of data,
+ * using binary BCH codes. It relies on the generic BCH library lib/bch.c.
+ *
+ * Copyright (C) 2011 Ivan Djelic <ivan.djelic at parrot.com>
+ *
+ * This file is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 or (at your option) any
+ * later version.
+ *
+ * This file is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this file; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/bitops.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/nand.h>
+#include <linux/mtd/nand_bch.h>
+#include <linux/bch.h>
+
+/**
+ * struct nand_bch_control - private NAND BCH control structure
+ * @bch: BCH control structure
+ * @ecclayout: private ecc layout for this BCH configuration
+ * @errloc: error location array
+ * @eccmask: XOR ecc mask, allows erased pages to be decoded as valid
+ */
+struct nand_bch_control {
+ struct bch_control *bch;
+ struct nand_ecclayout ecclayout;
+ unsigned int *errloc;
+ unsigned char *eccmask;
+};
+
+/**
+ * nand_bch_calculate_ecc - [NAND Interface] Calculate ECC for data block
+ * @mtd: MTD block structure
+ * @buf: input buffer with raw data
+ * @code: output buffer with ECC
+ */
+int nand_bch_calculate_ecc(struct mtd_info *mtd, const unsigned char *buf,
+ unsigned char *code)
+{
+ const struct nand_chip *chip = mtd->priv;
+ struct nand_bch_control *nbc = chip->ecc.priv;
+ unsigned int i;
+
+ memset(code, 0, chip->ecc.bytes);
+ encode_bch(nbc->bch, buf, chip->ecc.size, code);
+
+ /* apply mask so that an erased page is a valid codeword */
+ for (i = 0; i < chip->ecc.bytes; i++)
+ code[i] ^= nbc->eccmask[i];
+
+ return 0;
+}
+EXPORT_SYMBOL(nand_bch_calculate_ecc);
+
+/**
+ * nand_bch_correct_data - [NAND Interface] Detect and correct bit error(s)
+ * @mtd: MTD block structure
+ * @buf: raw data read from the chip
+ * @read_ecc: ECC from the chip
+ * @calc_ecc: the ECC calculated from raw data
+ *
+ * Detect and correct bit errors for a data byte block
+ */
+int nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
+ unsigned char *read_ecc, unsigned char *calc_ecc)
+{
+ const struct nand_chip *chip = mtd->priv;
+ struct nand_bch_control *nbc = chip->ecc.priv;
+ unsigned int *errloc = nbc->errloc;
+ int i, count;
+
+ count = decode_bch(nbc->bch, NULL, chip->ecc.size, read_ecc, calc_ecc,
+ NULL, errloc);
+ if (count > 0) {
+ for (i = 0; i < count; i++) {
+ if (errloc[i] < (chip->ecc.size*8))
+ /* error is located in data, correct it */
+ buf[errloc[i] >> 3] ^= (1 << (errloc[i] & 7));
+ /* else error in ecc, no action needed */
+
+ DEBUG(MTD_DEBUG_LEVEL0, "%s: corrected bitflip %u\n",
+ __func__, errloc[i]);
+ }
+ } else if (count < 0) {
+ printk(KERN_ERR "ecc unrecoverable error\n");
+ count = -1;
+ }
+ return count;
+}
+EXPORT_SYMBOL(nand_bch_correct_data);
+
+/**
+ * nand_bch_init - [NAND Interface] Initialize NAND BCH error correction
+ * @mtd: MTD block structure
+ * @eccsize: ecc block size in bytes
+ * @eccbytes: ecc length in bytes
+ * @ecclayout: output default layout
+ *
+ * Returns:
+ * a pointer to a new NAND BCH control structure, or NULL upon failure
+ *
+ * Initialize NAND BCH error correction. Parameters @eccsize and @eccbytes
+ * are used to compute BCH parameters m (Galois field order) and t (error
+ * correction capability). @eccbytes should be equal to the number of bytes
+ * required to store m*t bits, where m is such that 2^m-1 > @eccsize*8.
+ *
+ * Example: to configure 4 bit correction per 512 bytes, you should pass
+ * @eccsize = 512 (thus, m=13 is the smallest integer such that 2^m-1 > 512*8)
+ * @eccbytes = 7 (7 bytes are required to store m*t = 13*4 = 52 bits)
+ */
+struct nand_bch_control *
+nand_bch_init(struct mtd_info *mtd, unsigned int eccsize, unsigned int eccbytes,
+ struct nand_ecclayout **ecclayout)
+{
+ unsigned int m, t, eccsteps, i;
+ struct nand_ecclayout *layout;
+ struct nand_bch_control *nbc = NULL;
+ unsigned char *erased_page;
+
+ if (!eccsize || !eccbytes) {
+ printk(KERN_WARNING "ecc parameters not supplied\n");
+ goto fail;
+ }
+
+ m = fls(1+8*eccsize);
+ t = (eccbytes*8)/m;
+
+ nbc = kzalloc(sizeof(*nbc), GFP_KERNEL);
+ if (!nbc)
+ goto fail;
+
+ nbc->bch = init_bch(m, t, 0);
+ if (!nbc->bch)
+ goto fail;
+
+ /* verify that eccbytes has the expected value */
+ if (nbc->bch->ecc_bytes != eccbytes) {
+ printk(KERN_WARNING "invalid eccbytes %u, should be %u\n",
+ eccbytes, nbc->bch->ecc_bytes);
+ goto fail;
+ }
+
+ eccsteps = mtd->writesize/eccsize;
+
+ /* if no ecc placement scheme was provided, build one */
+ if (!*ecclayout) {
+
+ /* handle large page devices only */
+ if (mtd->oobsize < 64) {
+ printk(KERN_WARNING "must provide an oob scheme for "
+ "oobsize %d\n", mtd->oobsize);
+ goto fail;
+ }
+
+ layout = &nbc->ecclayout;
+ layout->eccbytes = eccsteps*eccbytes;
+
+ /* reserve 2 bytes for bad block marker */
+ if (layout->eccbytes+2 > mtd->oobsize) {
+ printk(KERN_WARNING "no suitable oob scheme available "
+ "for oobsize %d eccbytes %u\n", mtd->oobsize,
+ eccbytes);
+ goto fail;
+ }
+ /* put ecc bytes at oob tail */
+ for (i = 0; i < layout->eccbytes; i++)
+ layout->eccpos[i] = mtd->oobsize-layout->eccbytes+i;
+
+ layout->oobfree[0].offset = 2;
+ layout->oobfree[0].length = mtd->oobsize-2-layout->eccbytes;
+
+ *ecclayout = layout;
+ }
+
+ /* sanity checks */
+ if (8*(eccsize+eccbytes) >= (1 << m)) {
+ printk(KERN_WARNING "eccsize %u is too large\n", eccsize);
+ goto fail;
+ }
+ if ((*ecclayout)->eccbytes != (eccsteps*eccbytes)) {
+ printk(KERN_WARNING "invalid ecc layout\n");
+ goto fail;
+ }
+
+ nbc->eccmask = kmalloc(eccbytes, GFP_KERNEL);
+ nbc->errloc = kmalloc(t*sizeof(*nbc->errloc), GFP_KERNEL);
+ if (!nbc->eccmask || !nbc->errloc)
+ goto fail;
+ /*
+ * compute and store the inverted ecc of an erased ecc block
+ */
+ erased_page = kmalloc(eccsize, GFP_KERNEL);
+ if (!erased_page)
+ goto fail;
+
+ memset(erased_page, 0xff, eccsize);
+ memset(nbc->eccmask, 0, eccbytes);
+ encode_bch(nbc->bch, erased_page, eccsize, nbc->eccmask);
+ kfree(erased_page);
+
+ for (i = 0; i < eccbytes; i++)
+ nbc->eccmask[i] ^= 0xff;
+
+ return nbc;
+fail:
+ nand_bch_free(nbc);
+ return NULL;
+}
+EXPORT_SYMBOL(nand_bch_init);
+
+/**
+ * nand_bch_free - [NAND Interface] Release NAND BCH ECC resources
+ * @nbc: NAND BCH control structure
+ */
+void nand_bch_free(struct nand_bch_control *nbc)
+{
+ if (nbc) {
+ free_bch(nbc->bch);
+ kfree(nbc->errloc);
+ kfree(nbc->eccmask);
+ kfree(nbc);
+ }
+}
+EXPORT_SYMBOL(nand_bch_free);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Ivan Djelic <ivan.djelic at parrot.com>");
+MODULE_DESCRIPTION("NAND software BCH ECC support");
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 1f489b2..ae67ef5 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -140,6 +140,7 @@ typedef enum {
NAND_ECC_HW,
NAND_ECC_HW_SYNDROME,
NAND_ECC_HW_OOB_FIRST,
+ NAND_ECC_SOFT_BCH,
} nand_ecc_modes_t;
/*
@@ -339,6 +340,7 @@ struct nand_hw_control {
* @prepad: padding information for syndrome based ecc generators
* @postpad: padding information for syndrome based ecc generators
* @layout: ECC layout control struct pointer
+ * @priv: pointer to private ecc control data
* @hwctl: function to control hardware ecc generator. Must only
* be provided if an hardware ECC is available
* @calculate: function for ecc calculation or readback from ecc hardware
@@ -362,6 +364,7 @@ struct nand_ecc_ctrl {
int prepad;
int postpad;
struct nand_ecclayout *layout;
+ void *priv;
void (*hwctl)(struct mtd_info *mtd, int mode);
int (*calculate)(struct mtd_info *mtd, const uint8_t *dat,
uint8_t *ecc_code);
diff --git a/include/linux/mtd/nand_bch.h b/include/linux/mtd/nand_bch.h
new file mode 100644
index 0000000..94c206b
--- /dev/null
+++ b/include/linux/mtd/nand_bch.h
@@ -0,0 +1,74 @@
+/*
+ * include/mtd/nand_bch.h
+ *
+ * Copyright (C) 2011 Ivan Djelic <ivan.djelic at parrot.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This file is the header for the NAND BCH ECC implementation.
+ */
+
+#ifndef __MTD_NAND_BCH_H__
+#define __MTD_NAND_BCH_H__
+
+struct mtd_info;
+struct nand_bch_control;
+
+#if defined(CONFIG_MTD_NAND_ECC_BCH)
+
+static inline int mtd_nand_has_bch(void) { return 1; }
+
+/*
+ * Calculate BCH ecc code
+ */
+int nand_bch_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
+ u_char *ecc_code);
+
+/*
+ * Detect and correct bit errors
+ */
+int nand_bch_correct_data(struct mtd_info *mtd, u_char *dat, u_char *read_ecc,
+ u_char *calc_ecc);
+/*
+ * Initialize BCH encoder/decoder
+ */
+struct nand_bch_control *
+nand_bch_init(struct mtd_info *mtd, unsigned int eccsize,
+ unsigned int eccbytes, struct nand_ecclayout **ecclayout);
+/*
+ * Release BCH encoder/decoder resources
+ */
+void nand_bch_free(struct nand_bch_control *nbc);
+
+#else /* !CONFIG_MTD_NAND_ECC_BCH */
+
+static inline int mtd_nand_has_bch(void) { return 0; }
+
+static inline int
+nand_bch_calculate_ecc(struct mtd_info *mtd, const u_char *dat,
+ u_char *ecc_code)
+{
+ return -1;
+}
+
+static inline int
+nand_bch_correct_data(struct mtd_info *mtd, unsigned char *buf,
+ unsigned char *read_ecc, unsigned char *calc_ecc)
+{
+ return -1;
+}
+
+static inline struct nand_bch_control *
+nand_bch_init(struct mtd_info *mtd, unsigned int eccsize,
+ unsigned int eccbytes, struct nand_ecclayout **ecclayout)
+{
+ return NULL;
+}
+
+static inline void nand_bch_free(struct nand_bch_control *nbc) {}
+
+#endif /* CONFIG_MTD_NAND_ECC_BCH */
+
+#endif /* __MTD_NAND_BCH_H__ */
--
1.7.2.3
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