nand_bbt.c

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/*
 *  drivers/mtd/nand_bbt.c
 *
 *  Overview:
 *   Bad block table support for the NAND driver
 *
 *  Copyright © 2004 Thomas Gleixner ([email protected])
 *
 * 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_BBT_USE_FLASH) 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, then 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 * If one of the BBTs is out of date or does not exist it is (re)created.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_BBT_NO_OOB should be used (along with NAND_BBT_USE_FLASH, of
 * course): 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/bbm.h>
#include <linux/mtd/nand.h>
#include <linux/mtd/nand_ecc.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/vmalloc.h>
#include <linux/export.h>
#include <linux/string.h>

static int check_pattern_no_oob(uint8_t *buf, struct nand_bbt_descr *td)
{
    if (memcmp(buf, td->pattern, td->len))
        return -1;
    return 0;
}

static int check_pattern(uint8_t *buf, int len, int paglen, struct nand_bbt_descr *td)
{
    int 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)
        if (memchr_inv(p, 0xff, end))
            return -1;
    p += end;

    /* Compare the pattern */
    if (memcmp(p, td->pattern, td->len))
        return -1;

    if (td->options & NAND_BBT_SCANEMPTY) {
        p += td->len;
        end += td->len;
        if (memchr_inv(p, 0xff, len - end))
            return -1;
    }
    return 0;
}

static int check_short_pattern(uint8_t *buf, struct nand_bbt_descr *td)
{
    /* Compare the pattern */
    if (memcmp(buf + td->offs, td->pattern, td->len))
        return -1;
    return 0;
}

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;
}

static int read_bbt(struct mtd_info *mtd, uint8_t *buf, int page, int num,
        struct nand_bbt_descr *td, int offs)
{
    int res, ret = 0, 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 (mtd_is_eccerr(res)) {
                pr_info("nand_bbt: ECC error in BBT at "
                    "0x%012llx\n", from & ~mtd->writesize);
                return res;
            } else if (mtd_is_bitflip(res)) {
                pr_info("nand_bbt: corrected error in BBT at "
                    "0x%012llx\n", from & ~mtd->writesize);
                ret = res;
            } else {
                pr_info("nand_bbt: error reading BBT\n");
                return res;
            }
        }

        /* 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)) {
                    pr_info("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 it's matured we can
                 * move this message to pr_debug.
                 */
                pr_info("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 ret;
}

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_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);
}

static int scan_read_oob(struct mtd_info *mtd, uint8_t *buf, loff_t offs,
             size_t len)
{
    struct mtd_oob_ops ops;
    int res, ret = 0;

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

    while (len > 0) {
        ops.datbuf = buf;
        ops.len = min(len, (size_t)mtd->writesize);
        ops.oobbuf = buf + ops.len;

        res = mtd_read_oob(mtd, offs, &ops);
        if (res) {
            if (!mtd_is_bitflip_or_eccerr(res))
                return res;
            else if (mtd_is_eccerr(res) || !ret)
                ret = res;
        }

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

static int scan_read(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_data(mtd, buf, offs, td);
    else
        return scan_read_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_OPS_PLACE_OOB;
    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;
}

static void 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(mtd, buf, (loff_t)td->pages[0] << this->page_shift,
                  mtd->writesize, td);
        td->version[0] = buf[bbt_get_ver_offs(mtd, td)];
        pr_info("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(mtd, buf, (loff_t)md->pages[0] << this->page_shift,
                  mtd->writesize, md);
        md->version[0] = buf[bbt_get_ver_offs(mtd, md)];
        pr_info("Bad block table at page %d, version 0x%02X\n",
             md->pages[0], md->version[0]);
    }
}

/* 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 numpages)
{
    int ret, j;

    ret = scan_read_oob(mtd, buf, offs, readlen);
    /* Ignore ECC errors when checking for BBM */
    if (ret && !mtd_is_bitflip_or_eccerr(ret))
        return ret;

    for (j = 0; j < numpages; 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 numpages)
{
    struct mtd_oob_ops ops;
    int j, ret;

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

    for (j = 0; j < numpages; 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);
        /* Ignore ECC errors when checking for BBM */
        if (ret && !mtd_is_bitflip_or_eccerr(ret))
            return ret;

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

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

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, numpages, scanlen;
    int startblock;
    loff_t from;
    size_t readlen;

    pr_info("Scanning device for bad blocks\n");

    if (bd->options & NAND_BBT_SCANALLPAGES)
        numpages = 1 << (this->bbt_erase_shift - this->page_shift);
    else if (bd->options & NAND_BBT_SCAN2NDPAGE)
        numpages = 2;
    else
        numpages = 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 = numpages * 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) {
            pr_warn("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->bbt_options & NAND_BBT_SCANLASTPAGE)
        from += mtd->erasesize - (mtd->writesize * numpages);

    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, numpages);
        else
            ret = scan_block_fast(mtd, bd, from, buf, numpages);

        if (ret < 0)
            return ret;

        if (ret) {
            this->bbt[i >> 3] |= 0x03 << (i & 0x6);
            pr_warn("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;
}

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(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)
            pr_warn("Bad block table not found for chip %d\n", i);
        else
            pr_info("Bad block table found at page %d, version "
                 "0x%02X\n", td->pages[i], td->version[i]);
    }
    return 0;
}

static void 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);
}

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_OPS_PLACE_OOB;

    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;
        }
        pr_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) {
                    pr_info("nand_bbt: error reading block "
                        "for writing the bad block table\n");
                    return res;
                }
                pr_warn("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;

        pr_info("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:
    pr_warn("nand_bbt: error while writing bad block table %d\n", res);
    return res;
}

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);
}

static int check_create(struct mtd_info *mtd, uint8_t *buf, struct nand_bbt_descr *bd)
{
    int i, chips, writeops, create, chipsel, res, res2;
    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;
        create = 0;
        rd = NULL;
        rd2 = NULL;
        res = res2 = 0;
        /* Per chip or per device? */
        chipsel = (td->options & NAND_BBT_PERCHIP) ? i : -1;
        /* Mirrored table available? */
        if (md) {
            if (td->pages[i] == -1 && md->pages[i] == -1) {
                create = 1;
                writeops = 0x03;
            } else if (td->pages[i] == -1) {
                rd = md;
                writeops = 0x01;
            } else if (md->pages[i] == -1) {
                rd = td;
                writeops = 0x02;
            } else if (td->version[i] == md->version[i]) {
                rd = td;
                if (!(td->options & NAND_BBT_VERSION))
                    rd2 = md;
            } else if (((int8_t)(td->version[i] - md->version[i])) > 0) {
                rd = td;
                writeops = 0x02;
            } else {
                rd = md;
                writeops = 0x01;
            }
        } else {
            if (td->pages[i] == -1) {
                create = 1;
                writeops = 0x01;
            } else {
                rd = td;
            }
        }

        if (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->bbt_options & NAND_BBT_CREATE_EMPTY))
                create_bbt(mtd, buf, bd, chipsel);

            td->version[i] = 1;
            if (md)
                md->version[i] = 1;
        }

        /* Read back first? */
        if (rd) {
            res = read_abs_bbt(mtd, buf, rd, chipsel);
            if (mtd_is_eccerr(res)) {
                /* Mark table as invalid */
                rd->pages[i] = -1;
                rd->version[i] = 0;
                i--;
                continue;
            }
        }
        /* If they weren't versioned, read both */
        if (rd2) {
            res2 = read_abs_bbt(mtd, buf, rd2, chipsel);
            if (mtd_is_eccerr(res2)) {
                /* Mark table as invalid */
                rd2->pages[i] = -1;
                rd2->version[i] = 0;
                i--;
                continue;
            }
        }

        /* Scrub the flash table(s)? */
        if (mtd_is_bitflip(res) || mtd_is_bitflip(res2))
            writeops = 0x03;

        /* Update version numbers before writing */
        if (md) {
            td->version[i] = max(td->version[i], md->version[i]);
            md->version[i] = td->version[i];
        }

        /* 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;
}

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));
    }
}

static void verify_bbt_descr(struct mtd_info *mtd, struct nand_bbt_descr *bd)
{
    struct nand_chip *this = mtd->priv;
    u32 pattern_len;
    u32 bits;
    u32 table_size;

    if (!bd)
        return;

    pattern_len = bd->len;
    bits = bd->options & NAND_BBT_NRBITS_MSK;

    BUG_ON((this->bbt_options & NAND_BBT_NO_OOB) &&
            !(this->bbt_options & NAND_BBT_USE_FLASH));
    BUG_ON(!bits);

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

    if (bd->options & NAND_BBT_NO_OOB) {
        BUG_ON(!(this->bbt_options & NAND_BBT_USE_FLASH));
        BUG_ON(!(this->bbt_options & NAND_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));
}

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)
        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))) {
            pr_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) {
        kfree(this->bbt);
        this->bbt = NULL;
        return -ENOMEM;
    }

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

    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;
}

int nand_update_bbt(struct mtd_info *mtd, loff_t offs)
{
    struct nand_chip *this = mtd->priv;
    int len, res = 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)
        return -ENOMEM;

    /* 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 (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 (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 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 descriptors */
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 = NAND_BBT_SCAN_MAXBLOCKS,
    .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 = NAND_BBT_SCAN_MAXBLOCKS,
    .pattern = mirror_pattern
};

static struct nand_bbt_descr bbt_main_no_oob_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 = NAND_BBT_SCAN_MAXBLOCKS,
    .pattern = bbt_pattern
};

static struct nand_bbt_descr bbt_mirror_no_oob_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 = NAND_BBT_SCAN_MAXBLOCKS,
    .pattern = mirror_pattern
};

#define BADBLOCK_SCAN_MASK (~NAND_BBT_NO_OOB)

static int nand_create_badblock_pattern(struct nand_chip *this)
{
    struct nand_bbt_descr *bd;
    if (this->badblock_pattern) {
        pr_warn("Bad block pattern already allocated; not replacing\n");
        return -EINVAL;
    }
    bd = kzalloc(sizeof(*bd), GFP_KERNEL);
    if (!bd)
        return -ENOMEM;
    bd->options = this->bbt_options & BADBLOCK_SCAN_MASK;
    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;
}

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->bbt_options |= NAND_BBT_USE_FLASH;
        return nand_scan_bbt(mtd, &agand_flashbased);
    }

    /* Is a flash based bad block table requested? */
    if (this->bbt_options & NAND_BBT_USE_FLASH) {
        /* Use the default pattern descriptors */
        if (!this->bbt_td) {
            if (this->bbt_options & NAND_BBT_NO_OOB) {
                this->bbt_td = &bbt_main_no_oob_descr;
                this->bbt_md = &bbt_mirror_no_oob_descr;
            } else {
                this->bbt_td = &bbt_main_descr;
                this->bbt_md = &bbt_mirror_descr;
            }
        }
    } else {
        this->bbt_td = NULL;
        this->bbt_md = NULL;
    }

    if (!this->badblock_pattern)
        nand_create_badblock_pattern(this);

    return nand_scan_bbt(mtd, this->badblock_pattern);
}

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;

    pr_debug("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);
EXPORT_SYMBOL_GPL(nand_update_bbt);