/*
 *  drivers/mtd/nand_bbt.c
 *
 *  Overview:
 *   Bad block table support for the NAND driver
 *
 *  Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de)
 *
 * 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.
 *
 * Description:
 *
 * When nand_scan_bbt is called, then it tries to find the bad block table
 * depending on the options in the BBT descriptor(s). If no flash based BBT
 * (NAND_USE_FLASH_BBT) is specified then the device is scanned for factory
 * marked good / bad blocks. This information is used to create a memory BBT.
 * Once a new bad block is discovered then the "factory" information is updated
 * on the device.
 * If a flash based BBT is specified then the function first tries to find the
 * BBT on flash. If a BBT is found then the contents are read and the memory
 * based BBT is created. If a mirrored BBT is selected then the mirror is
 * searched too and the versions are compared. If the mirror has a greater
 * version number than the mirror BBT is used to build the memory based BBT.
 * If the tables are not versioned, then we "or" the bad block information.
 * If one of the BBTs is out of date or does not exist it is (re)created.
 * If no BBT exists at all then the device is scanned for factory marked
 * good / bad blocks and the bad block tables are created.
 *
 * For manufacturer created BBTs like the one found on M-SYS DOC devices
 * the BBT is searched and read but never created
 *
 * The auto generated bad block table is located in the last good blocks
 * of the device. The table is mirrored, so it can be updated eventually.
 * The table is marked in the OOB area with an ident pattern and a version
 * number which indicates which of both tables is more up to date. If the NAND
 * controller needs the complete OOB area for the ECC information then the
 * option NAND_USE_FLASH_BBT_NO_OOB should be used: it moves the ident pattern
 * and the version byte into the data area and the OOB area will remain
 * untouched.
 *
 * The table uses 2 bits per block
 * 11b:         block is good
 * 00b:         block is factory marked bad
 * 01b, 10b:    block is marked bad due to wear
 *
 * The memory bad block table uses the following scheme:
 * 00b:         block is good
 * 01b:         block is marked bad due to wear
 * 10b:         block is reserved (to protect the bbt area)
 * 11b:         block is factory marked bad
 *
 * Multichip devices like DOC store the bad block info per floor.
 *
 * Following assumptions are made:
 * - bbts start at a page boundary, if autolocated on a block boundary
 * - the space necessary for a bbt in FLASH does not exceed a block boundary
 *
 */

#include <linux/slab.h>
#include <linux/types.h>
#include <linux/mtd/mtd.h>
#include <linux/mtd/nand.h>
#include <linux/mtd/nand_ecc.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/vmalloc.h>

static int check_pattern_no_oob(uint8_t *buf, struct nand_bbt_descr *td)
{
        int ret;

        ret = memcmp(buf, td->pattern, td->len);
        if (!ret)
                return ret;
        return -1;
}

/**
 * check_pattern - [GENERIC] check if a pattern is in the buffer
 * @buf:        the buffer to search
 * @len:        the length of buffer to search
 * @paglen:     the pagelength
 * @td:         search pattern descriptor
 *
 * Check for a pattern at the given place. Used to search bad block
 * tables and good / bad block identifiers.
 * If the SCAN_EMPTY option is set then check, if all bytes except the
 * pattern area contain 0xff
 *
*/
static int check_pattern(uint8_t *buf, int len, int paglen, struct nand_bbt_descr *td)
{
        int i, end = 0;
        uint8_t *p = buf;

        if (td->options & NAND_BBT_NO_OOB)
                return check_pattern_no_oob(buf, td);

        end = paglen + td->offs;
        if (td->options & NAND_BBT_SCANEMPTY) {
                for (i = 0; i < end; i++) {
                        if (p[i] != 0xff)
                                return -1;
                }
        }
        p += end;

        /* Compare the pattern */
        for (i = 0; i < td->len; i++) {
                if (p[i] != td->pattern[i])
                        return -1;
        }

        /* Check both positions 1 and 6 for pattern? */
        if (td->options & NAND_BBT_SCANBYTE1AND6) {
                if (td->options & NAND_BBT_SCANEMPTY) {
                        p += td->len;
                        end += NAND_SMALL_BADBLOCK_POS - td->offs;
                        /* Check region between positions 1 and 6 */
                        for (i = 0; i < NAND_SMALL_BADBLOCK_POS - td->offs - td->len;
                                        i++) {
                                if (*p++ != 0xff)
                                        return -1;
                        }
                }
                else {
                        p += NAND_SMALL_BADBLOCK_POS - td->offs;
                }
                /* Compare the pattern */
                for (i = 0; i < td->len; i++) {
                        if (p[i] != td->pattern[i])
                                return -1;
                }
        }

        if (td->options & NAND_BBT_SCANEMPTY) {
                p += td->len;
                end += td->len;
                for (i = end; i < len; i++) {
                        if (*p++ != 0xff)
                                return -1;
                }
        }
        return 0;
}

/**
 * check_short_pattern - [GENERIC] check if a pattern is in the buffer
 * @buf:        the buffer to search
 * @td:         search pattern descriptor
 *
 * Check for a pattern at the given place. Used to search bad block
 * tables and good / bad block identifiers. Same as check_pattern, but
 * no optional empty check
 *
*/
static int check_short_pattern(uint8_t *buf, struct nand_bbt_descr *td)
{
        int i;
        uint8_t *p = buf;

        /* Compare the pattern */
        for (i = 0; i < td->len; i++) {
                if (p[td->offs + i] != td->pattern[i])
                        return -1;
        }
        /* Need to check location 1 AND 6? */
        if (td->options & NAND_BBT_SCANBYTE1AND6) {
                for (i = 0; i < td->len; i++) {
                        if (p[NAND_SMALL_BADBLOCK_POS + i] != td->pattern[i])
                                return -1;
                }
        }
        return 0;
}

/**
 * add_marker_len - compute the length of the marker in data area
 * @td:         BBT descriptor used for computation
 *
 * The length will be 0 if the markeris located in OOB area.
 */
static u32 add_marker_len(struct nand_bbt_descr *td)
{
        u32 len;

        if (!(td->options & NAND_BBT_NO_OOB))
                return 0;

        len = td->len;
        if (td->options & NAND_BBT_VERSION)
                len++;
        return len;
}

/**
 * read_bbt - [GENERIC] Read the bad block table starting from page
 * @mtd:        MTD device structure
 * @buf:        temporary buffer
 * @page:       the starting page
 * @num:        the number of bbt descriptors to read
 * @td:         the bbt describtion table
 * @offs:       offset in the memory table
 *
 * Read the bad block table starting from page.
 *
 */
static int read_bbt(struct mtd_info *mtd, uint8_t *buf, int page, int num,
                struct nand_bbt_descr *td, int offs)
{
        int res, i, j, act = 0;
        struct nand_chip *this = mtd->priv;
        size_t retlen, len, totlen;
        loff_t from;
        int bits = td->options & NAND_BBT_NRBITS_MSK;
        uint8_t msk = (uint8_t) ((1 << bits) - 1);
        u32 marker_len;
        int reserved_block_code = td->reserved_block_code;

        totlen = (num * bits) >> 3;
        marker_len = add_marker_len(td);
        from = ((loff_t) page) << this->page_shift;

        while (totlen) {
                len = min(totlen, (size_t) (1 << this->bbt_erase_shift));
                if (marker_len) {
                        /*
                         * In case the BBT marker is not in the OOB area it
                         * will be just in the first page.
                         */
                        len -= marker_len;
                        from += marker_len;
                        marker_len = 0;
                }
                res = mtd->read(mtd, from, len, &retlen, buf);
                if (res < 0) {
                        if (retlen != len) {
                                printk(KERN_INFO "nand_bbt: Error reading bad block table\n");
                                return res;
                        }
                        printk(KERN_WARNING "nand_bbt: ECC error while reading bad block table\n");
                }

                /* Analyse data */
                for (i = 0; i < len; i++) {
                        uint8_t dat = buf[i];
                        for (j = 0; j < 8; j += bits, act += 2) {
                                uint8_t tmp = (dat >> j) & msk;
                                if (tmp == msk)
                                        continue;
                                if (reserved_block_code && (tmp == reserved_block_code)) {
                                        printk(KERN_DEBUG "nand_read_bbt: Reserved block at 0x%012llx\n",
                                               (loff_t)((offs << 2) + (act >> 1)) << this->bbt_erase_shift);
                                        this->bbt[offs + (act >> 3)] |= 0x2 << (act & 0x06);
                                        mtd->ecc_stats.bbtblocks++;
                                        continue;
                                }
                                /* Leave it for now, if its matured we can move this
                                 * message to MTD_DEBUG_LEVEL0 */
                                printk(KERN_DEBUG "nand_read_bbt: Bad block at 0x%012llx\n",
                                       (loff_t)((offs << 2) + (act >> 1)) << this->bbt_erase_shift);
                                /* Factory marked bad or worn out ? */
                                if (tmp == 0)
                                        this->bbt[offs + (act >> 3)] |= 0x3 << (act & 0x06);
                                else
                                        this->bbt[offs + (act >> 3)] |= 0x1 << (act & 0x06);
                                mtd->ecc_stats.badblocks++;
                        }
                }
                totlen -= len;
                from += len;
        }
        return 0;
}

/**
 * read_abs_bbt - [GENERIC] Read the bad block table starting at a given page
 * @mtd:        MTD device structure
 * @buf:        temporary buffer
 * @td:         descriptor for the bad block table
 * @chip:       read the table for a specific chip, -1 read all chips.
 *              Applies only if NAND_BBT_PERCHIP option is set
 *
 * Read the bad block table for all chips starting at a given page
 * We assume that the bbt bits are in consecutive order.
*/
static int read_abs_bbt(struct mtd_info *mtd, uint8_t *buf, struct nand_bbt_descr *td, int chip)
{
        struct nand_chip *this = mtd->priv;
        int res = 0, i;

        if (td->options & NAND_BBT_PERCHIP) {
                int offs = 0;
                for (i = 0; i < this->numchips; i++) {
                        if (chip == -1 || chip == i)
                                res = read_bbt(mtd, buf, td->pages[i],
                                        this->chipsize >> this->bbt_erase_shift,
                                        td, offs);
                        if (res)
                                return res;
                        offs += this->chipsize >> (this->bbt_erase_shift + 2);
                }
        } else {
                res = read_bbt(mtd, buf, td->pages[0],
                                mtd->size >> this->bbt_erase_shift, td, 0);
                if (res)
                        return res;
        }
        return 0;
}

/*
 * BBT marker is in the first page, no OOB.
 */
static int scan_read_raw_data(struct mtd_info *mtd, uint8_t *buf, loff_t offs,
                         struct nand_bbt_descr *td)
{
        size_t retlen;
        size_t len;

        len = td->len;
        if (td->options & NAND_BBT_VERSION)
                len++;

        return mtd->read(mtd, offs, len, &retlen, buf);
}

/*
 * Scan read raw data from flash
 */
static int scan_read_raw_oob(struct mtd_info *mtd, uint8_t *buf, loff_t offs,
                         size_t len)
{
        struct mtd_oob_ops ops;
        int res;

        ops.mode = MTD_OOB_RAW;
        ops.ooboffs = 0;
        ops.ooblen = mtd->oobsize;


        while (len > 0) {
                if (len <= mtd->writesize) {
                        ops.oobbuf = buf + len;
                        ops.datbuf = buf;
                        ops.len = len;
                        return mtd->read_oob(mtd, offs, &ops);
                } else {
                        ops.oobbuf = buf + mtd->writesize;
                        ops.datbuf = buf;
                        ops.len = mtd->writesize;
                        res = mtd->read_oob(mtd, offs, &ops);

                        if (res)
                                return res;
                }

                buf += mtd->oobsize + mtd->writesize;
                len -= mtd->writesize;
        }
        return 0;
}

static int scan_read_raw(struct mtd_info *mtd, uint8_t *buf, loff_t offs,
                         size_t len, struct nand_bbt_descr *td)
{
        if (td->options & NAND_BBT_NO_OOB)
                return scan_read_raw_data(mtd, buf, offs, td);
        else
                return scan_read_raw_oob(mtd, buf, offs, len);
}

/*
 * Scan write data with oob to flash
 */
static int scan_write_bbt(struct mtd_info *mtd, loff_t offs, size_t len,
                          uint8_t *buf, uint8_t *oob)
{
        struct mtd_oob_ops ops;

        ops.mode = MTD_OOB_PLACE;
        ops.ooboffs = 0;
        ops.ooblen = mtd->oobsize;
        ops.datbuf = buf;
        ops.oobbuf = oob;
        ops.len = len;

        return mtd->write_oob(mtd, offs, &ops);
}

static u32 bbt_get_ver_offs(struct mtd_info *mtd, struct nand_bbt_descr *td)
{
        u32 ver_offs = td->veroffs;

        if (!(td->options & NAND_BBT_NO_OOB))
                ver_offs += mtd->writesize;
        return ver_offs;
}

/**
 * read_abs_bbts - [GENERIC] Read the bad block table(s) for all chips starting at a given page
 * @mtd:        MTD device structure
 * @buf:        temporary buffer
 * @td:         descriptor for the bad block table
 * @md:         descriptor for the bad block table mirror
 *
 * Read the bad block table(s) for all chips starting at a given page
 * We assume that the bbt bits are in consecutive order.
 *
*/
static int read_abs_bbts(struct mtd_info *mtd, uint8_t *buf,
                         struct nand_bbt_descr *td, struct nand_bbt_descr *md)
{
        struct nand_chip *this = mtd->priv;

        /* Read the primary version, if available */
        if (td->options & NAND_BBT_VERSION) {
                scan_read_raw(mtd, buf, (loff_t)td->pages[0] << this->page_shift,
                              mtd->writesize, td);
                td->version[0] = buf[bbt_get_ver_offs(mtd, td)];
                printk(KERN_DEBUG "Bad block table at page %d, version 0x%02X\n",
                       td->pages[0], td->version[0]);
        }

        /* Read the mirror version, if available */
        if (md && (md->options & NAND_BBT_VERSION)) {
                scan_read_raw(mtd, buf, (loff_t)md->pages[0] << this->page_shift,
                              mtd->writesize, td);
                md->version[0] = buf[bbt_get_ver_offs(mtd, md)];
                printk(KERN_DEBUG "Bad block table at page %d, version 0x%02X\n",
                       md->pages[0], md->version[0]);
        }
        return 1;
}

/*
 * Scan a given block full
 */
static int scan_block_full(struct mtd_info *mtd, struct nand_bbt_descr *bd,
                           loff_t offs, uint8_t *buf, size_t readlen,
                           int scanlen, int len)
{
        int ret, j;

        ret = scan_read_raw_oob(mtd, buf, offs, readlen);
        if (ret)
                return ret;

        for (j = 0; j < len; j++, buf += scanlen) {
                if (check_pattern(buf, scanlen, mtd->writesize, bd))
                        return 1;
        }
        return 0;
}

/*
 * Scan a given block partially
 */
static int scan_block_fast(struct mtd_info *mtd, struct nand_bbt_descr *bd,
                           loff_t offs, uint8_t *buf, int len)
{
        struct mtd_oob_ops ops;
        int j, ret;

        ops.ooblen = mtd->oobsize;
        ops.oobbuf = buf;
        ops.ooboffs = 0;
        ops.datbuf = NULL;
        ops.mode = MTD_OOB_PLACE;

        for (j = 0; j < len; j++) {
                /*
                 * Read the full oob until read_oob is fixed to
                 * handle single byte reads for 16 bit
                 * buswidth
                 */
                ret = mtd->read_oob(mtd, offs, &ops);
                if (ret)
                        return ret;

                if (check_short_pattern(buf, bd))
                        return 1;

                offs += mtd->writesize;
        }
        return 0;
}

/**
 * create_bbt - [GENERIC] Create a bad block table by scanning the device
 * @mtd:        MTD device structure
 * @buf:        temporary buffer
 * @bd:         descriptor for the good/bad block search pattern
 * @chip:       create the table for a specific chip, -1 read all chips.
 *              Applies only if NAND_BBT_PERCHIP option is set
 *
 * Create a bad block table by scanning the device
 * for the given good/bad block identify pattern
 */
static int create_bbt(struct mtd_info *mtd, uint8_t *buf,
        struct nand_bbt_descr *bd, int chip)
{
        struct nand_chip *this = mtd->priv;
        int i, numblocks, len, scanlen;
        int startblock;
        loff_t from;
        size_t readlen;

        printk(KERN_INFO "Scanning device for bad blocks\n");

        if (bd->options & NAND_BBT_SCANALLPAGES)
                len = 1 << (this->bbt_erase_shift - this->page_shift);
        else if (bd->options & NAND_BBT_SCAN2NDPAGE)
                len = 2;
        else
                len = 1;

        if (!(bd->options & NAND_BBT_SCANEMPTY)) {
                /* We need only read few bytes from the OOB area */
                scanlen = 0;
                readlen = bd->len;
        } else {
                /* Full page content should be read */
                scanlen = mtd->writesize + mtd->oobsize;
                readlen = len * mtd->writesize;
        }

        if (chip == -1) {
                /* Note that numblocks is 2 * (real numblocks) here, see i+=2
                 * below as it makes shifting and masking less painful */
                numblocks = mtd->size >> (this->bbt_erase_shift - 1);
                startblock = 0;
                from = 0;
        } else {
                if (chip >= this->numchips) {
                        printk(KERN_WARNING "create_bbt(): chipnr (%d) > available chips (%d)\n",
                               chip + 1, this->numchips);
                        return -EINVAL;
                }
                numblocks = this->chipsize >> (this->bbt_erase_shift - 1);
                startblock = chip * numblocks;
                numblocks += startblock;
                from = (loff_t)startblock << (this->bbt_erase_shift - 1);
        }

        if (this->options & NAND_BBT_SCANLASTPAGE)
                from += mtd->erasesize - (mtd->writesize * len);

        for (i = startblock; i < numblocks;) {
                int ret;

                BUG_ON(bd->options & NAND_BBT_NO_OOB);

                if (bd->options & NAND_BBT_SCANALLPAGES)
                        ret = scan_block_full(mtd, bd, from, buf, readlen,
                                              scanlen, len);
                else
                        ret = scan_block_fast(mtd, bd, from, buf, len);

                if (ret < 0)
                        return ret;

                if (ret) {
                        this->bbt[i >> 3] |= 0x03 << (i & 0x6);
                        printk(KERN_WARNING "Bad eraseblock %d at 0x%012llx\n",
                               i >> 1, (unsigned long long)from);
                        mtd->ecc_stats.badblocks++;
                }

                i += 2;
                from += (1 << this->bbt_erase_shift);
        }
        return 0;
}

/**
 * search_bbt - [GENERIC] scan the device for a specific bad block table
 * @mtd:        MTD device structure
 * @buf:        temporary buffer
 * @td:         descriptor for the bad block table
 *
 * Read the bad block table by searching for a given ident pattern.
 * Search is preformed either from the beginning up or from the end of
 * the device downwards. The search starts always at the start of a
 * block.
 * If the option NAND_BBT_PERCHIP is given, each chip is searched
 * for a bbt, which contains the bad block information of this chip.
 * This is necessary to provide support for certain DOC devices.
 *
 * The bbt ident pattern resides in the oob area of the first page
 * in a block.
 */
static int search_bbt(struct mtd_info *mtd, uint8_t *buf, struct nand_bbt_descr *td)
{
        struct nand_chip *this = mtd->priv;
        int i, chips;
        int bits, startblock, block, dir;
        int scanlen = mtd->writesize + mtd->oobsize;
        int bbtblocks;
        int blocktopage = this->bbt_erase_shift - this->page_shift;

        /* Search direction top -> down ? */
        if (td->options & NAND_BBT_LASTBLOCK) {
                startblock = (mtd->size >> this->bbt_erase_shift) - 1;
                dir = -1;
        } else {
                startblock = 0;
                dir = 1;
        }

        /* Do we have a bbt per chip ? */
        if (td->options & NAND_BBT_PERCHIP) {
                chips = this->numchips;
                bbtblocks = this->chipsize >> this->bbt_erase_shift;
                startblock &= bbtblocks - 1;
        } else {
                chips = 1;
                bbtblocks = mtd->size >> this->bbt_erase_shift;
        }

        /* Number of bits for each erase block in the bbt */
        bits = td->options & NAND_BBT_NRBITS_MSK;

        for (i = 0; i < chips; i++) {
                /* Reset version information */
                td->version[i] = 0;
                td->pages[i] = -1;
                /* Scan the maximum number of blocks */
                for (block = 0; block < td->maxblocks; block++) {

                        int actblock = startblock + dir * block;
                        loff_t offs = (loff_t)actblock << this->bbt_erase_shift;

                        /* Read first page */
                        scan_read_raw(mtd, buf, offs, mtd->writesize, td);
                        if (!check_pattern(buf, scanlen, mtd->writesize, td)) {
                                td->pages[i] = actblock << blocktopage;
                                if (td->options & NAND_BBT_VERSION) {
                                        offs = bbt_get_ver_offs(mtd, td);
                                        td->version[i] = buf[offs];
                                }
                                break;
                        }
                }
                startblock += this->chipsize >> this->bbt_erase_shift;
        }
        /* Check, if we found a bbt for each requested chip */
        for (i = 0; i < chips; i++) {
                if (td->pages[i] == -1)
                        printk(KERN_WARNING "Bad block table not found for chip %d\n", i);
                else
                        printk(KERN_DEBUG "Bad block table found at page %d, version 0x%02X\n", td->pages[i],
                               td->version[i]);
        }
        return 0;
}

/**
 * search_read_bbts - [GENERIC] scan the device for bad block table(s)
 * @mtd:        MTD device structure
 * @buf:        temporary buffer
 * @td:         descriptor for the bad block table
 * @md:         descriptor for the bad block table mirror
 *
 * Search and read the bad block table(s)
*/
static int search_read_bbts(struct mtd_info *mtd, uint8_t * buf, struct nand_bbt_descr *td, struct nand_bbt_descr *md)
{
        /* Search the primary table */
        search_bbt(mtd, buf, td);

        /* Search the mirror table */
        if (md)
                search_bbt(mtd, buf, md);

        /* Force result check */
        return 1;
}

/**
 * write_bbt - [GENERIC] (Re)write the bad block table
 *
 * @mtd:        MTD device structure
 * @buf:        temporary buffer
 * @td:         descriptor for the bad block table
 * @md:         descriptor for the bad block table mirror
 * @chipsel:    selector for a specific chip, -1 for all
 *
 * (Re)write the bad block table
 *
*/
static int write_bbt(struct mtd_info *mtd, uint8_t *buf,
                     struct nand_bbt_descr *td, struct nand_bbt_descr *md,
                     int chipsel)
{
        struct nand_chip *this = mtd->priv;
        struct erase_info einfo;
        int i, j, res, chip = 0;
        int bits, startblock, dir, page, offs, numblocks, sft, sftmsk;
        int nrchips, bbtoffs, pageoffs, ooboffs;
        uint8_t msk[4];
        uint8_t rcode = td->reserved_block_code;
        size_t retlen, len = 0;
        loff_t to;
        struct mtd_oob_ops ops;

        ops.ooblen = mtd->oobsize;
        ops.ooboffs = 0;
        ops.datbuf = NULL;
        ops.mode = MTD_OOB_PLACE;

        if (!rcode)
                rcode = 0xff;
        /* Write bad block table per chip rather than per device ? */
        if (td->options & NAND_BBT_PERCHIP) {
                numblocks = (int)(this->chipsize >> this->bbt_erase_shift);
                /* Full device write or specific chip ? */
                if (chipsel == -1) {
                        nrchips = this->numchips;
                } else {
                        nrchips = chipsel + 1;
                        chip = chipsel;
                }
        } else {
                numblocks = (int)(mtd->size >> this->bbt_erase_shift);
                nrchips = 1;
        }

        /* Loop through the chips */
        for (; chip < nrchips; chip++) {

                /* There was already a version of the table, reuse the page
                 * This applies for absolute placement too, as we have the
                 * page nr. in td->pages.
                 */
                if (td->pages[chip] != -1) {
                        page = td->pages[chip];
                        goto write;
                }

                /* Automatic placement of the bad block table */
                /* Search direction top -> down ? */
                if (td->options & NAND_BBT_LASTBLOCK) {
                        startblock = numblocks * (chip + 1) - 1;
                        dir = -1;
                } else {
                        startblock = chip * numblocks;
                        dir = 1;
                }

                for (i = 0; i < td->maxblocks; i++) {
                        int block = startblock + dir * i;
                        /* Check, if the block is bad */
                        switch ((this->bbt[block >> 2] >>
                                 (2 * (block & 0x03))) & 0x03) {
                        case 0x01:
                        case 0x03:
                                continue;
                        }
                        page = block <<
                                (this->bbt_erase_shift - this->page_shift);
                        /* Check, if the block is used by the mirror table */
                        if (!md || md->pages[chip] != page)
                                goto write;
                }
                printk(KERN_ERR "No space left to write bad block table\n");
                return -ENOSPC;
        write:

                /* Set up shift count and masks for the flash table */
                bits = td->options & NAND_BBT_NRBITS_MSK;
                msk[2] = ~rcode;
                switch (bits) {
                case 1: sft = 3; sftmsk = 0x07; msk[0] = 0x00; msk[1] = 0x01;
                        msk[3] = 0x01;
                        break;
                case 2: sft = 2; sftmsk = 0x06; msk[0] = 0x00; msk[1] = 0x01;
                        msk[3] = 0x03;
                        break;
                case 4: sft = 1; sftmsk = 0x04; msk[0] = 0x00; msk[1] = 0x0C;
                        msk[3] = 0x0f;
                        break;
                case 8: sft = 0; sftmsk = 0x00; msk[0] = 0x00; msk[1] = 0x0F;
                        msk[3] = 0xff;
                        break;
                default: return -EINVAL;
                }

                bbtoffs = chip * (numblocks >> 2);

                to = ((loff_t) page) << this->page_shift;

                /* Must we save the block contents ? */
                if (td->options & NAND_BBT_SAVECONTENT) {
                        /* Make it block aligned */
                        to &= ~((loff_t) ((1 << this->bbt_erase_shift) - 1));
                        len = 1 << this->bbt_erase_shift;
                        res = mtd->read(mtd, to, len, &retlen, buf);
                        if (res < 0) {
                                if (retlen != len) {
                                        printk(KERN_INFO "nand_bbt: Error "
                                               "reading block for writing "
                                               "the bad block table\n");
                                        return res;
                                }
                                printk(KERN_WARNING "nand_bbt: ECC error "
                                       "while reading block for writing "
                                       "bad block table\n");
                        }
                        /* Read oob data */
                        ops.ooblen = (len >> this->page_shift) * mtd->oobsize;
                        ops.oobbuf = &buf[len];
                        res = mtd->read_oob(mtd, to + mtd->writesize, &ops);
                        if (res < 0 || ops.oobretlen != ops.ooblen)
                                goto outerr;

                        /* Calc the byte offset in the buffer */
                        pageoffs = page - (int)(to >> this->page_shift);
                        offs = pageoffs << this->page_shift;
                        /* Preset the bbt area with 0xff */
                        memset(&buf[offs], 0xff, (size_t) (numblocks >> sft));
                        ooboffs = len + (pageoffs * mtd->oobsize);

                } else if (td->options & NAND_BBT_NO_OOB) {
                        ooboffs = 0;
                        offs = td->len;
                        /* the version byte */
                        if (td->options & NAND_BBT_VERSION)
                                offs++;
                        /* Calc length */
                        len = (size_t) (numblocks >> sft);
                        len += offs;
                        /* Make it page aligned ! */
                        len = ALIGN(len, mtd->writesize);
                        /* Preset the buffer with 0xff */
                        memset(buf, 0xff, len);
                        /* Pattern is located at the begin of first page */
                        memcpy(buf, td->pattern, td->len);
                } else {
                        /* Calc length */
                        len = (size_t) (numblocks >> sft);
                        /* Make it page aligned ! */
                        len = ALIGN(len, mtd->writesize);
                        /* Preset the buffer with 0xff */
                        memset(buf, 0xff, len +
                               (len >> this->page_shift)* mtd->oobsize);
                        offs = 0;
                        ooboffs = len;
                        /* Pattern is located in oob area of first page */
                        memcpy(&buf[ooboffs + td->offs], td->pattern, td->len);
                }

                if (td->options & NAND_BBT_VERSION)
                        buf[ooboffs + td->veroffs] = td->version[chip];

                /* walk through the memory table */
                for (i = 0; i < numblocks;) {
                        uint8_t dat;
                        dat = this->bbt[bbtoffs + (i >> 2)];
                        for (j = 0; j < 4; j++, i++) {
                                int sftcnt = (i << (3 - sft)) & sftmsk;
                                /* Do not store the reserved bbt blocks ! */
                                buf[offs + (i >> sft)] &=
                                        ~(msk[dat & 0x03] << sftcnt);
                                dat >>= 2;
                        }
                }

                memset(&einfo, 0, sizeof(einfo));
                einfo.mtd = mtd;
                einfo.addr = to;
                einfo.len = 1 << this->bbt_erase_shift;
                res = nand_erase_nand(mtd, &einfo, 1);
                if (res < 0)
                        goto outerr;

                res = scan_write_bbt(mtd, to, len, buf,
                                td->options & NAND_BBT_NO_OOB ? NULL :
                                &buf[len]);
                if (res < 0)
                        goto outerr;

                printk(KERN_DEBUG "Bad block table written to 0x%012llx, version "
                       "0x%02X\n", (unsigned long long)to, td->version[chip]);

                /* Mark it as used */
                td->pages[chip] = page;
        }
        return 0;

 outerr:
        printk(KERN_WARNING
               "nand_bbt: Error while writing bad block table %d\n", res);
        return res;
}

/**
 * nand_memory_bbt - [GENERIC] create a memory based bad block table
 * @mtd:        MTD device structure
 * @bd:         descriptor for the good/bad block search pattern
 *
 * The function creates a memory based bbt by scanning the device
 * for manufacturer / software marked good / bad blocks
*/
static inline int nand_memory_bbt(struct mtd_info *mtd, struct nand_bbt_descr *bd)
{
        struct nand_chip *this = mtd->priv;

        bd->options &= ~NAND_BBT_SCANEMPTY;
        return create_bbt(mtd, this->buffers->databuf, bd, -1);
}

/**
 * check_create - [GENERIC] create and write bbt(s) if necessary
 * @mtd:        MTD device structure
 * @buf:        temporary buffer
 * @bd:         descriptor for the good/bad block search pattern
 *
 * The function checks the results of the previous call to read_bbt
 * and creates / updates the bbt(s) if necessary
 * Creation is necessary if no bbt was found for the chip/device
 * Update is necessary if one of the tables is missing or the
 * version nr. of one table is less than the other
*/
static int check_create(struct mtd_info *mtd, uint8_t *buf, struct nand_bbt_descr *bd)
{
        int i, chips, writeops, chipsel, res;
        struct nand_chip *this = mtd->priv;
        struct nand_bbt_descr *td = this->bbt_td;
        struct nand_bbt_descr *md = this->bbt_md;
        struct nand_bbt_descr *rd, *rd2;

        /* Do we have a bbt per chip ? */
        if (td->options & NAND_BBT_PERCHIP)
                chips = this->numchips;
        else
                chips = 1;

        for (i = 0; i < chips; i++) {
                writeops = 0;
                rd = NULL;
                rd2 = NULL;
                /* Per chip or per device ? */
                chipsel = (td->options & NAND_BBT_PERCHIP) ? i : -1;
                /* Mirrored table avilable ? */
                if (md) {
                        if (td->pages[i] == -1 && md->pages[i] == -1) {
                                writeops = 0x03;
                                goto create;
                        }

                        if (td->pages[i] == -1) {
                                rd = md;
                                td->version[i] = md->version[i];
                                writeops = 1;
                                goto writecheck;
                        }

                        if (md->pages[i] == -1) {
                                rd = td;
                                md->version[i] = td->version[i];
                                writeops = 2;
                                goto writecheck;
                        }

                        if (td->version[i] == md->version[i]) {
                                rd = td;
                                if (!(td->options & NAND_BBT_VERSION))
                                        rd2 = md;
                                goto writecheck;
                        }

                        if (((int8_t) (td->version[i] - md->version[i])) > 0) {
                                rd = td;
                                md->version[i] = td->version[i];
                                writeops = 2;
                        } else {
                                rd = md;
                                td->version[i] = md->version[i];
                                writeops = 1;
                        }

                        goto writecheck;

                } else {
                        if (td->pages[i] == -1) {
                                writeops = 0x01;
                                goto create;
                        }
                        rd = td;
                        goto writecheck;
                }
        create:
                /* Create the bad block table by scanning the device ? */
                if (!(td->options & NAND_BBT_CREATE))
                        continue;

                /* Create the table in memory by scanning the chip(s) */
                if (!(this->options & NAND_CREATE_EMPTY_BBT))
                        create_bbt(mtd, buf, bd, chipsel);

                td->version[i] = 1;
                if (md)
                        md->version[i] = 1;
        writecheck:
                /* read back first ? */
                if (rd)
                        read_abs_bbt(mtd, buf, rd, chipsel);
                /* If they weren't versioned, read both. */
                if (rd2)
                        read_abs_bbt(mtd, buf, rd2, chipsel);

                /* Write the bad block table to the device ? */
                if ((writeops & 0x01) && (td->options & NAND_BBT_WRITE)) {
                        res = write_bbt(mtd, buf, td, md, chipsel);
                        if (res < 0)
                                return res;
                }

                /* Write the mirror bad block table to the device ? */
                if ((writeops & 0x02) && md && (md->options & NAND_BBT_WRITE)) {
                        res = write_bbt(mtd, buf, md, td, chipsel);
                        if (res < 0)
                                return res;
                }
        }
        return 0;
}

/**
 * mark_bbt_regions - [GENERIC] mark the bad block table regions
 * @mtd:        MTD device structure
 * @td:         bad block table descriptor
 *
 * The bad block table regions are marked as "bad" to prevent
 * accidental erasures / writes. The regions are identified by
 * the mark 0x02.
*/
static void mark_bbt_region(struct mtd_info *mtd, struct nand_bbt_descr *td)
{
        struct nand_chip *this = mtd->priv;
        int i, j, chips, block, nrblocks, update;
        uint8_t oldval, newval;

        /* Do we have a bbt per chip ? */
        if (td->options & NAND_BBT_PERCHIP) {
                chips = this->numchips;
                nrblocks = (int)(this->chipsize >> this->bbt_erase_shift);
        } else {
                chips = 1;
                nrblocks = (int)(mtd->size >> this->bbt_erase_shift);
        }

        for (i = 0; i < chips; i++) {
                if ((td->options & NAND_BBT_ABSPAGE) ||
                    !(td->options & NAND_BBT_WRITE)) {
                        if (td->pages[i] == -1)
                                continue;
                        block = td->pages[i] >> (this->bbt_erase_shift - this->page_shift);
                        block <<= 1;
                        oldval = this->bbt[(block >> 3)];
                        newval = oldval | (0x2 << (block & 0x06));
                        this->bbt[(block >> 3)] = newval;
                        if ((oldval != newval) && td->reserved_block_code)
                                nand_update_bbt(mtd, (loff_t)block << (this->bbt_erase_shift - 1));
                        continue;
                }
                update = 0;
                if (td->options & NAND_BBT_LASTBLOCK)
                        block = ((i + 1) * nrblocks) - td->maxblocks;
                else
                        block = i * nrblocks;
                block <<= 1;
                for (j = 0; j < td->maxblocks; j++) {
                        oldval = this->bbt[(block >> 3)];
                        newval = oldval | (0x2 << (block & 0x06));
                        this->bbt[(block >> 3)] = newval;
                        if (oldval != newval)
                                update = 1;
                        block += 2;
                }
                /* If we want reserved blocks to be recorded to flash, and some
                   new ones have been marked, then we need to update the stored
                   bbts.  This should only happen once. */
                if (update && td->reserved_block_code)
                        nand_update_bbt(mtd, (loff_t)(block - 2) << (this->bbt_erase_shift - 1));
        }
}

/**
 * verify_bbt_descr - verify the bad block description
 * @mtd:        MTD device structure
 * @bd:         the table to verify
 *
 * This functions performs a few sanity checks on the bad block description
 * table.
 */
static void verify_bbt_descr(struct mtd_info *mtd, struct nand_bbt_descr *bd)
{
        struct nand_chip *this = mtd->priv;
        u32 pattern_len = bd->len;
        u32 bits = bd->options & NAND_BBT_NRBITS_MSK;
        u32 table_size;

        if (!bd)
                return;
        BUG_ON((this->options & NAND_USE_FLASH_BBT_NO_OOB) &&
                        !(this->options & NAND_USE_FLASH_BBT));
        BUG_ON(!bits);

        if (bd->options & NAND_BBT_VERSION)
                pattern_len++;

        if (bd->options & NAND_BBT_NO_OOB) {
                BUG_ON(!(this->options & NAND_USE_FLASH_BBT));
                BUG_ON(!(this->options & NAND_USE_FLASH_BBT_NO_OOB));
                BUG_ON(bd->offs);
                if (bd->options & NAND_BBT_VERSION)
                        BUG_ON(bd->veroffs != bd->len);
                BUG_ON(bd->options & NAND_BBT_SAVECONTENT);
        }

        if (bd->options & NAND_BBT_PERCHIP)
                table_size = this->chipsize >> this->bbt_erase_shift;
        else
                table_size = mtd->size >> this->bbt_erase_shift;
        table_size >>= 3;
        table_size *= bits;
        if (bd->options & NAND_BBT_NO_OOB)
                table_size += pattern_len;
        BUG_ON(table_size > (1 << this->bbt_erase_shift));
}

/**
 * nand_scan_bbt - [NAND Interface] scan, find, read and maybe create bad block table(s)
 * @mtd:        MTD device structure
 * @bd:         descriptor for the good/bad block search pattern
 *
 * The function checks, if a bad block table(s) is/are already
 * available. If not it scans the device for manufacturer
 * marked good / bad blocks and writes the bad block table(s) to
 * the selected place.
 *
 * The bad block table memory is allocated here. It must be freed
 * by calling the nand_free_bbt function.
 *
*/
int nand_scan_bbt(struct mtd_info *mtd, struct nand_bbt_descr *bd)
{
        struct nand_chip *this = mtd->priv;
        int len, res = 0;
        uint8_t *buf;
        struct nand_bbt_descr *td = this->bbt_td;
        struct nand_bbt_descr *md = this->bbt_md;

        len = mtd->size >> (this->bbt_erase_shift + 2);
        /* Allocate memory (2bit per block) and clear the memory bad block table */
        this->bbt = kzalloc(len, GFP_KERNEL);
        if (!this->bbt) {
                printk(KERN_ERR "nand_scan_bbt: Out of memory\n");
                return -ENOMEM;
        }

        /* If no primary table decriptor is given, scan the device
         * to build a memory based bad block table
         */
        if (!td) {
                if ((res = nand_memory_bbt(mtd, bd))) {
                        printk(KERN_ERR "nand_bbt: Can't scan flash and build the RAM-based BBT\n");
                        kfree(this->bbt);
                        this->bbt = NULL;
                }
                return res;
        }
        verify_bbt_descr(mtd, td);
        verify_bbt_descr(mtd, md);

        /* Allocate a temporary buffer for one eraseblock incl. oob */
        len = (1 << this->bbt_erase_shift);
        len += (len >> this->page_shift) * mtd->oobsize;
        buf = vmalloc(len);
        if (!buf) {
                printk(KERN_ERR "nand_bbt: Out of memory\n");
                kfree(this->bbt);
                this->bbt = NULL;
                return -ENOMEM;
        }

        /* Is the bbt at a given page ? */
        if (td->options & NAND_BBT_ABSPAGE) {
                res = read_abs_bbts(mtd, buf, td, md);
        } else {
                /* Search the bad block table using a pattern in oob */
                res = search_read_bbts(mtd, buf, td, md);
        }

        if (res)
                res = check_create(mtd, buf, bd);

        /* Prevent the bbt regions from erasing / writing */
        mark_bbt_region(mtd, td);
        if (md)
                mark_bbt_region(mtd, md);

        vfree(buf);
        return res;
}

/**
 * nand_update_bbt - [NAND Interface] update bad block table(s)
 * @mtd:        MTD device structure
 * @offs:       the offset of the newly marked block
 *
 * The function updates the bad block table(s)
*/
int nand_update_bbt(struct mtd_info *mtd, loff_t offs)
{
        struct nand_chip *this = mtd->priv;
        int len, res = 0, writeops = 0;
        int chip, chipsel;
        uint8_t *buf;
        struct nand_bbt_descr *td = this->bbt_td;
        struct nand_bbt_descr *md = this->bbt_md;

        if (!this->bbt || !td)
                return -EINVAL;

        /* Allocate a temporary buffer for one eraseblock incl. oob */
        len = (1 << this->bbt_erase_shift);
        len += (len >> this->page_shift) * mtd->oobsize;
        buf = kmalloc(len, GFP_KERNEL);
        if (!buf) {
                printk(KERN_ERR "nand_update_bbt: Out of memory\n");
                return -ENOMEM;
        }

        writeops = md != NULL ? 0x03 : 0x01;

        /* Do we have a bbt per chip ? */
        if (td->options & NAND_BBT_PERCHIP) {
                chip = (int)(offs >> this->chip_shift);
                chipsel = chip;
        } else {
                chip = 0;
                chipsel = -1;
        }

        td->version[chip]++;
        if (md)
                md->version[chip]++;

        /* Write the bad block table to the device ? */
        if ((writeops & 0x01) && (td->options & NAND_BBT_WRITE)) {
                res = write_bbt(mtd, buf, td, md, chipsel);
                if (res < 0)
                        goto out;
        }
        /* Write the mirror bad block table to the device ? */
        if ((writeops & 0x02) && md && (md->options & NAND_BBT_WRITE)) {
                res = write_bbt(mtd, buf, md, td, chipsel);
        }

 out:
        kfree(buf);
        return res;
}

/* Define some generic bad / good block scan pattern which are used
 * while scanning a device for factory marked good / bad blocks. */
static uint8_t scan_ff_pattern[] = { 0xff, 0xff };

static struct nand_bbt_descr smallpage_flashbased = {
        .options = NAND_BBT_SCAN2NDPAGE,
        .offs = NAND_SMALL_BADBLOCK_POS,
        .len = 1,
        .pattern = scan_ff_pattern
};

static struct nand_bbt_descr largepage_flashbased = {
        .options = NAND_BBT_SCAN2NDPAGE,
        .offs = NAND_LARGE_BADBLOCK_POS,
        .len = 2,
        .pattern = scan_ff_pattern
};

static uint8_t scan_agand_pattern[] = { 0x1C, 0x71, 0xC7, 0x1C, 0x71, 0xC7 };

static struct nand_bbt_descr agand_flashbased = {
        .options = NAND_BBT_SCANEMPTY | NAND_BBT_SCANALLPAGES,
        .offs = 0x20,
        .len = 6,
        .pattern = scan_agand_pattern
};

/* Generic flash bbt decriptors
*/
static uint8_t bbt_pattern[] = {'B', 'b', 't', '0' };
static uint8_t mirror_pattern[] = {'1', 't', 'b', 'B' };

static struct nand_bbt_descr bbt_main_descr = {
        .options = NAND_BBT_LASTBLOCK | NAND_BBT_CREATE | NAND_BBT_WRITE
                | NAND_BBT_2BIT | NAND_BBT_VERSION | NAND_BBT_PERCHIP,
        .offs = 8,
        .len = 4,
        .veroffs = 12,
        .maxblocks = 4,
        .pattern = bbt_pattern
};

static struct nand_bbt_descr bbt_mirror_descr = {
        .options = NAND_BBT_LASTBLOCK | NAND_BBT_CREATE | NAND_BBT_WRITE
                | NAND_BBT_2BIT | NAND_BBT_VERSION | NAND_BBT_PERCHIP,
        .offs = 8,
        .len = 4,
        .veroffs = 12,
        .maxblocks = 4,
        .pattern = mirror_pattern
};

static struct nand_bbt_descr bbt_main_no_bbt_descr = {
        .options = NAND_BBT_LASTBLOCK | NAND_BBT_CREATE | NAND_BBT_WRITE
                | NAND_BBT_2BIT | NAND_BBT_VERSION | NAND_BBT_PERCHIP
                | NAND_BBT_NO_OOB,
        .len = 4,
        .veroffs = 4,
        .maxblocks = 4,
        .pattern = bbt_pattern
};

static struct nand_bbt_descr bbt_mirror_no_bbt_descr = {
        .options = NAND_BBT_LASTBLOCK | NAND_BBT_CREATE | NAND_BBT_WRITE
                | NAND_BBT_2BIT | NAND_BBT_VERSION | NAND_BBT_PERCHIP
                | NAND_BBT_NO_OOB,
        .len = 4,
        .veroffs = 4,
        .maxblocks = 4,
        .pattern = mirror_pattern
};

#define BBT_SCAN_OPTIONS (NAND_BBT_SCANLASTPAGE | NAND_BBT_SCAN2NDPAGE | \
                NAND_BBT_SCANBYTE1AND6)
/**
 * nand_create_default_bbt_descr - [Internal] Creates a BBT descriptor structure
 * @this:       NAND chip to create descriptor for
 *
 * This function allocates and initializes a nand_bbt_descr for BBM detection
 * based on the properties of "this". The new descriptor is stored in
 * this->badblock_pattern. Thus, this->badblock_pattern should be NULL when
 * passed to this function.
 *
 * TODO: Handle other flags, replace other static structs
 *        (e.g. handle NAND_BBT_FLASH for flash-based BBT,
 *             replace smallpage_flashbased)
 *
 */
static int nand_create_default_bbt_descr(struct nand_chip *this)
{
        struct nand_bbt_descr *bd;
        if (this->badblock_pattern) {
                printk(KERN_WARNING "BBT descr already allocated; not replacing.\n");
                return -EINVAL;
        }
        bd = kzalloc(sizeof(*bd), GFP_KERNEL);
        if (!bd) {
                printk(KERN_ERR "nand_create_default_bbt_descr: Out of memory\n");
                return -ENOMEM;
        }
        bd->options = this->options & BBT_SCAN_OPTIONS;
        bd->offs = this->badblockpos;
        bd->len = (this->options & NAND_BUSWIDTH_16) ? 2 : 1;
        bd->pattern = scan_ff_pattern;
        bd->options |= NAND_BBT_DYNAMICSTRUCT;
        this->badblock_pattern = bd;
        return 0;
}

/**
 * nand_default_bbt - [NAND Interface] Select a default bad block table for the device
 * @mtd:        MTD device structure
 *
 * This function selects the default bad block table
 * support for the device and calls the nand_scan_bbt function
 *
*/
int nand_default_bbt(struct mtd_info *mtd)
{
        struct nand_chip *this = mtd->priv;

        /* Default for AG-AND. We must use a flash based
         * bad block table as the devices have factory marked
         * _good_ blocks. Erasing those blocks leads to loss
         * of the good / bad information, so we _must_ store
         * this information in a good / bad table during
         * startup
         */
        if (this->options & NAND_IS_AND) {
                /* Use the default pattern descriptors */
                if (!this->bbt_td) {
                        this->bbt_td = &bbt_main_descr;
                        this->bbt_md = &bbt_mirror_descr;
                }
                this->options |= NAND_USE_FLASH_BBT;
                return nand_scan_bbt(mtd, &agand_flashbased);
        }

        /* Is a flash based bad block table requested ? */
        if (this->options & NAND_USE_FLASH_BBT) {
                /* Use the default pattern descriptors */
                if (!this->bbt_td) {
                        if (this->options & NAND_USE_FLASH_BBT_NO_OOB) {
                                this->bbt_td = &bbt_main_no_bbt_descr;
                                this->bbt_md = &bbt_mirror_no_bbt_descr;
                        } else {
                                this->bbt_td = &bbt_main_descr;
                                this->bbt_md = &bbt_mirror_descr;
                        }
                }
                if (!this->badblock_pattern) {
                        this->badblock_pattern = (mtd->writesize > 512) ? &largepage_flashbased : &smallpage_flashbased;
                }
        } else {
                this->bbt_td = NULL;
                this->bbt_md = NULL;
                if (!this->badblock_pattern)
                        nand_create_default_bbt_descr(this);
        }
        return nand_scan_bbt(mtd, this->badblock_pattern);
}

/**
 * nand_isbad_bbt - [NAND Interface] Check if a block is bad
 * @mtd:        MTD device structure
 * @offs:       offset in the device
 * @allowbbt:   allow access to bad block table region
 *
*/
int nand_isbad_bbt(struct mtd_info *mtd, loff_t offs, int allowbbt)
{
        struct nand_chip *this = mtd->priv;
        int block;
        uint8_t res;

        /* Get block number * 2 */
        block = (int)(offs >> (this->bbt_erase_shift - 1));
        res = (this->bbt[block >> 3] >> (block & 0x06)) & 0x03;

        DEBUG(MTD_DEBUG_LEVEL2, "nand_isbad_bbt(): bbt info for offs 0x%08x: (block %d) 0x%02x\n",
              (unsigned int)offs, block >> 1, res);

        switch ((int)res) {
        case 0x00:
                return 0;
        case 0x01:
                return 1;
        case 0x02:
                return allowbbt ? 0 : 1;
        }
        return 1;
}

EXPORT_SYMBOL(nand_scan_bbt);
EXPORT_SYMBOL(nand_default_bbt);