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mtd: nand: add software BCH ECC support

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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@parrot.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
This commit is contained in:
Ivan Djelic 2011-03-11 11:05:33 +01:00 committed by David Woodhouse
parent 89d8d32060
commit 193bd40026
6 changed files with 373 additions and 1 deletions
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15
drivers/mtd/nand/Kconfig
View file

@ -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

1
drivers/mtd/nand/Makefile
View file

@ -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

40
drivers/mtd/nand/nand_base.c
View file

@ -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);

243
drivers/mtd/nand/nand_bch.c Normal file
View file

@ -0,0 +1,243 @@
/*
* 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 © 2011 Ivan Djelic <ivan.djelic@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@parrot.com>");
MODULE_DESCRIPTION("NAND software BCH ECC support");

3
include/linux/mtd/nand.h
View file

@ -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);

72
include/linux/mtd/nand_bch.h Normal file
View file

@ -0,0 +1,72 @@
/*
* Copyright © 2011 Ivan Djelic <ivan.djelic@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__ */