/*
 * MTD device concatenation layer
 *
 * Copyright © 2002 Robert Kaiser <rkaiser@sysgo.de>
 * Copyright © 2002-2010 David Woodhouse <dwmw2@infradead.org>
 *
 * NAND support by Christian Gan <cgan@iders.ca>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/backing-dev.h>

#include <linux/mtd/mtd.h>
#include <linux/mtd/concat.h>

#include <asm/div64.h>

/*
 * Our storage structure:
 * Subdev points to an array of pointers to struct mtd_info objects
 * which is allocated along with this structure
 *
 */
struct mtd_concat {
        struct mtd_info mtd;
        int num_subdev;
        struct mtd_info **subdev;
};

/*
 * how to calculate the size required for the above structure,
 * including the pointer array subdev points to:
 */
#define SIZEOF_STRUCT_MTD_CONCAT(num_subdev)    \
        ((sizeof(struct mtd_concat) + (num_subdev) * sizeof(struct mtd_info *)))

/*
 * Given a pointer to the MTD object in the mtd_concat structure,
 * we can retrieve the pointer to that structure with this macro.
 */
#define CONCAT(x)  ((struct mtd_concat *)(x))

/*
 * MTD methods which look up the relevant subdevice, translate the
 * effective address and pass through to the subdevice.
 */

static int
concat_read(struct mtd_info *mtd, loff_t from, size_t len,
            size_t * retlen, u_char * buf)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int ret = 0, err;
        int i;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];
                size_t size, retsize;

                if (from >= subdev->size) {
                        /* Not destined for this subdev */
                        size = 0;
                        from -= subdev->size;
                        continue;
                }
                if (from + len > subdev->size)
                        /* First part goes into this subdev */
                        size = subdev->size - from;
                else
                        /* Entire transaction goes into this subdev */
                        size = len;

                err = mtd_read(subdev, from, size, &retsize, buf);

                /* Save information about bitflips! */
                if (unlikely(err)) {
                        if (mtd_is_eccerr(err)) {
                                mtd->ecc_stats.failed++;
                                ret = err;
                        } else if (mtd_is_bitflip(err)) {
                                mtd->ecc_stats.corrected++;
                                /* Do not overwrite -EBADMSG !! */
                                if (!ret)
                                        ret = err;
                        } else
                                return err;
                }

                *retlen += retsize;
                len -= size;
                if (len == 0)
                        return ret;

                buf += size;
                from = 0;
        }
        return -EINVAL;
}

static int
concat_write(struct mtd_info *mtd, loff_t to, size_t len,
             size_t * retlen, const u_char * buf)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int err = -EINVAL;
        int i;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];
                size_t size, retsize;

                if (to >= subdev->size) {
                        size = 0;
                        to -= subdev->size;
                        continue;
                }
                if (to + len > subdev->size)
                        size = subdev->size - to;
                else
                        size = len;

                err = mtd_write(subdev, to, size, &retsize, buf);
                if (err)
                        break;

                *retlen += retsize;
                len -= size;
                if (len == 0)
                        break;

                err = -EINVAL;
                buf += size;
                to = 0;
        }
        return err;
}

static int
concat_writev(struct mtd_info *mtd, const struct kvec *vecs,
                unsigned long count, loff_t to, size_t * retlen)
{
        struct mtd_concat *concat = CONCAT(mtd);
        struct kvec *vecs_copy;
        unsigned long entry_low, entry_high;
        size_t total_len = 0;
        int i;
        int err = -EINVAL;

        /* Calculate total length of data */
        for (i = 0; i < count; i++)
                total_len += vecs[i].iov_len;

        /* Check alignment */
        if (mtd->writesize > 1) {
                uint64_t __to = to;
                if (do_div(__to, mtd->writesize) || (total_len % mtd->writesize))
                        return -EINVAL;
        }

        /* make a copy of vecs */
        vecs_copy = kmemdup(vecs, sizeof(struct kvec) * count, GFP_KERNEL);
        if (!vecs_copy)
                return -ENOMEM;

        entry_low = 0;
        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];
                size_t size, wsize, retsize, old_iov_len;

                if (to >= subdev->size) {
                        to -= subdev->size;
                        continue;
                }

                size = min_t(uint64_t, total_len, subdev->size - to);
                wsize = size; /* store for future use */

                entry_high = entry_low;
                while (entry_high < count) {
                        if (size <= vecs_copy[entry_high].iov_len)
                                break;
                        size -= vecs_copy[entry_high++].iov_len;
                }

                old_iov_len = vecs_copy[entry_high].iov_len;
                vecs_copy[entry_high].iov_len = size;

                err = mtd_writev(subdev, &vecs_copy[entry_low],
                                 entry_high - entry_low + 1, to, &retsize);

                vecs_copy[entry_high].iov_len = old_iov_len - size;
                vecs_copy[entry_high].iov_base += size;

                entry_low = entry_high;

                if (err)
                        break;

                *retlen += retsize;
                total_len -= wsize;

                if (total_len == 0)
                        break;

                err = -EINVAL;
                to = 0;
        }

        kfree(vecs_copy);
        return err;
}

static int
concat_read_oob(struct mtd_info *mtd, loff_t from, struct mtd_oob_ops *ops)
{
        struct mtd_concat *concat = CONCAT(mtd);
        struct mtd_oob_ops devops = *ops;
        int i, err, ret = 0;

        ops->retlen = ops->oobretlen = 0;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];

                if (from >= subdev->size) {
                        from -= subdev->size;
                        continue;
                }

                /* partial read ? */
                if (from + devops.len > subdev->size)
                        devops.len = subdev->size - from;

                err = mtd_read_oob(subdev, from, &devops);
                ops->retlen += devops.retlen;
                ops->oobretlen += devops.oobretlen;

                /* Save information about bitflips! */
                if (unlikely(err)) {
                        if (mtd_is_eccerr(err)) {
                                mtd->ecc_stats.failed++;
                                ret = err;
                        } else if (mtd_is_bitflip(err)) {
                                mtd->ecc_stats.corrected++;
                                /* Do not overwrite -EBADMSG !! */
                                if (!ret)
                                        ret = err;
                        } else
                                return err;
                }

                if (devops.datbuf) {
                        devops.len = ops->len - ops->retlen;
                        if (!devops.len)
                                return ret;
                        devops.datbuf += devops.retlen;
                }
                if (devops.oobbuf) {
                        devops.ooblen = ops->ooblen - ops->oobretlen;
                        if (!devops.ooblen)
                                return ret;
                        devops.oobbuf += ops->oobretlen;
                }

                from = 0;
        }
        return -EINVAL;
}

static int
concat_write_oob(struct mtd_info *mtd, loff_t to, struct mtd_oob_ops *ops)
{
        struct mtd_concat *concat = CONCAT(mtd);
        struct mtd_oob_ops devops = *ops;
        int i, err;

        if (!(mtd->flags & MTD_WRITEABLE))
                return -EROFS;

        ops->retlen = ops->oobretlen = 0;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];

                if (to >= subdev->size) {
                        to -= subdev->size;
                        continue;
                }

                /* partial write ? */
                if (to + devops.len > subdev->size)
                        devops.len = subdev->size - to;

                err = mtd_write_oob(subdev, to, &devops);
                ops->retlen += devops.oobretlen;
                if (err)
                        return err;

                if (devops.datbuf) {
                        devops.len = ops->len - ops->retlen;
                        if (!devops.len)
                                return 0;
                        devops.datbuf += devops.retlen;
                }
                if (devops.oobbuf) {
                        devops.ooblen = ops->ooblen - ops->oobretlen;
                        if (!devops.ooblen)
                                return 0;
                        devops.oobbuf += devops.oobretlen;
                }
                to = 0;
        }
        return -EINVAL;
}

static void concat_erase_callback(struct erase_info *instr)
{
        wake_up((wait_queue_head_t *) instr->priv);
}

static int concat_dev_erase(struct mtd_info *mtd, struct erase_info *erase)
{
        int err;
        wait_queue_head_t waitq;
        DECLARE_WAITQUEUE(wait, current);

        /*
         * This code was stol^H^H^H^Hinspired by mtdchar.c
         */
        init_waitqueue_head(&waitq);

        erase->mtd = mtd;
        erase->callback = concat_erase_callback;
        erase->priv = (unsigned long) &waitq;

        /*
         * FIXME: Allow INTERRUPTIBLE. Which means
         * not having the wait_queue head on the stack.
         */
        err = mtd_erase(mtd, erase);
        if (!err) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                add_wait_queue(&waitq, &wait);
                if (erase->state != MTD_ERASE_DONE
                    && erase->state != MTD_ERASE_FAILED)
                        schedule();
                remove_wait_queue(&waitq, &wait);
                set_current_state(TASK_RUNNING);

                err = (erase->state == MTD_ERASE_FAILED) ? -EIO : 0;
        }
        return err;
}

static int concat_erase(struct mtd_info *mtd, struct erase_info *instr)
{
        struct mtd_concat *concat = CONCAT(mtd);
        struct mtd_info *subdev;
        int i, err;
        uint64_t length, offset = 0;
        struct erase_info *erase;

        /*
         * Check for proper erase block alignment of the to-be-erased area.
         * It is easier to do this based on the super device's erase
         * region info rather than looking at each particular sub-device
         * in turn.
         */
        if (!concat->mtd.numeraseregions) {
                /* the easy case: device has uniform erase block size */
                if (instr->addr & (concat->mtd.erasesize - 1))
                        return -EINVAL;
                if (instr->len & (concat->mtd.erasesize - 1))
                        return -EINVAL;
        } else {
                /* device has variable erase size */
                struct mtd_erase_region_info *erase_regions =
                    concat->mtd.eraseregions;

                /*
                 * Find the erase region where the to-be-erased area begins:
                 */
                for (i = 0; i < concat->mtd.numeraseregions &&
                     instr->addr >= erase_regions[i].offset; i++) ;
                --i;

                /*
                 * Now erase_regions[i] is the region in which the
                 * to-be-erased area begins. Verify that the starting
                 * offset is aligned to this region's erase size:
                 */
                if (i < 0 || instr->addr & (erase_regions[i].erasesize - 1))
                        return -EINVAL;

                /*
                 * now find the erase region where the to-be-erased area ends:
                 */
                for (; i < concat->mtd.numeraseregions &&
                     (instr->addr + instr->len) >= erase_regions[i].offset;
                     ++i) ;
                --i;
                /*
                 * check if the ending offset is aligned to this region's erase size
                 */
                if (i < 0 || ((instr->addr + instr->len) &
                                        (erase_regions[i].erasesize - 1)))
                        return -EINVAL;
        }

        /* make a local copy of instr to avoid modifying the caller's struct */
        erase = kmalloc(sizeof (struct erase_info), GFP_KERNEL);

        if (!erase)
                return -ENOMEM;

        *erase = *instr;
        length = instr->len;

        /*
         * find the subdevice where the to-be-erased area begins, adjust
         * starting offset to be relative to the subdevice start
         */
        for (i = 0; i < concat->num_subdev; i++) {
                subdev = concat->subdev[i];
                if (subdev->size <= erase->addr) {
                        erase->addr -= subdev->size;
                        offset += subdev->size;
                } else {
                        break;
                }
        }

        /* must never happen since size limit has been verified above */
        BUG_ON(i >= concat->num_subdev);

        /* now do the erase: */
        err = 0;
        for (; length > 0; i++) {
                /* loop for all subdevices affected by this request */
                subdev = concat->subdev[i];     /* get current subdevice */

                /* limit length to subdevice's size: */
                if (erase->addr + length > subdev->size)
                        erase->len = subdev->size - erase->addr;
                else
                        erase->len = length;

                length -= erase->len;
                if ((err = concat_dev_erase(subdev, erase))) {
                        /* sanity check: should never happen since
                         * block alignment has been checked above */
                        BUG_ON(err == -EINVAL);
                        if (erase->fail_addr != MTD_FAIL_ADDR_UNKNOWN)
                                instr->fail_addr = erase->fail_addr + offset;
                        break;
                }
                /*
                 * erase->addr specifies the offset of the area to be
                 * erased *within the current subdevice*. It can be
                 * non-zero only the first time through this loop, i.e.
                 * for the first subdevice where blocks need to be erased.
                 * All the following erases must begin at the start of the
                 * current subdevice, i.e. at offset zero.
                 */
                erase->addr = 0;
                offset += subdev->size;
        }
        instr->state = erase->state;
        kfree(erase);
        if (err)
                return err;

        if (instr->callback)
                instr->callback(instr);
        return 0;
}

static int concat_lock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int i, err = -EINVAL;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];
                uint64_t size;

                if (ofs >= subdev->size) {
                        size = 0;
                        ofs -= subdev->size;
                        continue;
                }
                if (ofs + len > subdev->size)
                        size = subdev->size - ofs;
                else
                        size = len;

                err = mtd_lock(subdev, ofs, size);
                if (err)
                        break;

                len -= size;
                if (len == 0)
                        break;

                err = -EINVAL;
                ofs = 0;
        }

        return err;
}

static int concat_unlock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int i, err = 0;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];
                uint64_t size;

                if (ofs >= subdev->size) {
                        size = 0;
                        ofs -= subdev->size;
                        continue;
                }
                if (ofs + len > subdev->size)
                        size = subdev->size - ofs;
                else
                        size = len;

                err = mtd_unlock(subdev, ofs, size);
                if (err)
                        break;

                len -= size;
                if (len == 0)
                        break;

                err = -EINVAL;
                ofs = 0;
        }

        return err;
}

static void concat_sync(struct mtd_info *mtd)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int i;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];
                mtd_sync(subdev);
        }
}

static int concat_suspend(struct mtd_info *mtd)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int i, rc = 0;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];
                if ((rc = mtd_suspend(subdev)) < 0)
                        return rc;
        }
        return rc;
}

static void concat_resume(struct mtd_info *mtd)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int i;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];
                mtd_resume(subdev);
        }
}

static int concat_block_isbad(struct mtd_info *mtd, loff_t ofs)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int i, res = 0;

        if (!mtd_can_have_bb(concat->subdev[0]))
                return res;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];

                if (ofs >= subdev->size) {
                        ofs -= subdev->size;
                        continue;
                }

                res = mtd_block_isbad(subdev, ofs);
                break;
        }

        return res;
}

static int concat_block_markbad(struct mtd_info *mtd, loff_t ofs)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int i, err = -EINVAL;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];

                if (ofs >= subdev->size) {
                        ofs -= subdev->size;
                        continue;
                }

                err = mtd_block_markbad(subdev, ofs);
                if (!err)
                        mtd->ecc_stats.badblocks++;
                break;
        }

        return err;
}

/*
 * try to support NOMMU mmaps on concatenated devices
 * - we don't support subdev spanning as we can't guarantee it'll work
 */
static unsigned long concat_get_unmapped_area(struct mtd_info *mtd,
                                              unsigned long len,
                                              unsigned long offset,
                                              unsigned long flags)
{
        struct mtd_concat *concat = CONCAT(mtd);
        int i;

        for (i = 0; i < concat->num_subdev; i++) {
                struct mtd_info *subdev = concat->subdev[i];

                if (offset >= subdev->size) {
                        offset -= subdev->size;
                        continue;
                }

                return mtd_get_unmapped_area(subdev, len, offset, flags);
        }

        return (unsigned long) -ENOSYS;
}

/*
 * This function constructs a virtual MTD device by concatenating
 * num_devs MTD devices. A pointer to the new device object is
 * stored to *new_dev upon success. This function does _not_
 * register any devices: this is the caller's responsibility.
 */
struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],   /* subdevices to concatenate */
                                   int num_devs,        /* number of subdevices      */
                                   const char *name)
{                               /* name for the new device   */
        int i;
        size_t size;
        struct mtd_concat *concat;
        uint32_t max_erasesize, curr_erasesize;
        int num_erase_region;
        int max_writebufsize = 0;

        printk(KERN_NOTICE "Concatenating MTD devices:\n");
        for (i = 0; i < num_devs; i++)
                printk(KERN_NOTICE "(%d): \"%s\"\n", i, subdev[i]->name);
        printk(KERN_NOTICE "into device \"%s\"\n", name);

        /* allocate the device structure */
        size = SIZEOF_STRUCT_MTD_CONCAT(num_devs);
        concat = kzalloc(size, GFP_KERNEL);
        if (!concat) {
                printk
                    ("memory allocation error while creating concatenated device \"%s\"\n",
                     name);
                return NULL;
        }
        concat->subdev = (struct mtd_info **) (concat + 1);

        /*
         * Set up the new "super" device's MTD object structure, check for
         * incompatibilities between the subdevices.
         */
        concat->mtd.type = subdev[0]->type;
        concat->mtd.flags = subdev[0]->flags;
        concat->mtd.size = subdev[0]->size;
        concat->mtd.erasesize = subdev[0]->erasesize;
        concat->mtd.writesize = subdev[0]->writesize;

        for (i = 0; i < num_devs; i++)
                if (max_writebufsize < subdev[i]->writebufsize)
                        max_writebufsize = subdev[i]->writebufsize;
        concat->mtd.writebufsize = max_writebufsize;

        concat->mtd.subpage_sft = subdev[0]->subpage_sft;
        concat->mtd.oobsize = subdev[0]->oobsize;
        concat->mtd.oobavail = subdev[0]->oobavail;
        if (subdev[0]->_writev)
                concat->mtd._writev = concat_writev;
        if (subdev[0]->_read_oob)
                concat->mtd._read_oob = concat_read_oob;
        if (subdev[0]->_write_oob)
                concat->mtd._write_oob = concat_write_oob;
        if (subdev[0]->_block_isbad)
                concat->mtd._block_isbad = concat_block_isbad;
        if (subdev[0]->_block_markbad)
                concat->mtd._block_markbad = concat_block_markbad;

        concat->mtd.ecc_stats.badblocks = subdev[0]->ecc_stats.badblocks;

        concat->mtd.backing_dev_info = subdev[0]->backing_dev_info;

        concat->subdev[0] = subdev[0];

        for (i = 1; i < num_devs; i++) {
                if (concat->mtd.type != subdev[i]->type) {
                        kfree(concat);
                        printk("Incompatible device type on \"%s\"\n",
                               subdev[i]->name);
                        return NULL;
                }
                if (concat->mtd.flags != subdev[i]->flags) {
                        /*
                         * Expect all flags except MTD_WRITEABLE to be
                         * equal on all subdevices.
                         */
                        if ((concat->mtd.flags ^ subdev[i]->
                             flags) & ~MTD_WRITEABLE) {
                                kfree(concat);
                                printk("Incompatible device flags on \"%s\"\n",
                                       subdev[i]->name);
                                return NULL;
                        } else
                                /* if writeable attribute differs,
                                   make super device writeable */
                                concat->mtd.flags |=
                                    subdev[i]->flags & MTD_WRITEABLE;
                }

                /* only permit direct mapping if the BDIs are all the same
                 * - copy-mapping is still permitted
                 */
                if (concat->mtd.backing_dev_info !=
                    subdev[i]->backing_dev_info)
                        concat->mtd.backing_dev_info =
                                &default_backing_dev_info;

                concat->mtd.size += subdev[i]->size;
                concat->mtd.ecc_stats.badblocks +=
                        subdev[i]->ecc_stats.badblocks;
                if (concat->mtd.writesize   !=  subdev[i]->writesize ||
                    concat->mtd.subpage_sft != subdev[i]->subpage_sft ||
                    concat->mtd.oobsize    !=  subdev[i]->oobsize ||
                    !concat->mtd._read_oob  != !subdev[i]->_read_oob ||
                    !concat->mtd._write_oob != !subdev[i]->_write_oob) {
                        kfree(concat);
                        printk("Incompatible OOB or ECC data on \"%s\"\n",
                               subdev[i]->name);
                        return NULL;
                }
                concat->subdev[i] = subdev[i];

        }

        concat->mtd.ecclayout = subdev[0]->ecclayout;

        concat->num_subdev = num_devs;
        concat->mtd.name = name;

        concat->mtd._erase = concat_erase;
        concat->mtd._read = concat_read;
        concat->mtd._write = concat_write;
        concat->mtd._sync = concat_sync;
        concat->mtd._lock = concat_lock;
        concat->mtd._unlock = concat_unlock;
        concat->mtd._suspend = concat_suspend;
        concat->mtd._resume = concat_resume;
        concat->mtd._get_unmapped_area = concat_get_unmapped_area;

        /*
         * Combine the erase block size info of the subdevices:
         *
         * first, walk the map of the new device and see how
         * many changes in erase size we have
         */
        max_erasesize = curr_erasesize = subdev[0]->erasesize;
        num_erase_region = 1;
        for (i = 0; i < num_devs; i++) {
                if (subdev[i]->numeraseregions == 0) {
                        /* current subdevice has uniform erase size */
                        if (subdev[i]->erasesize != curr_erasesize) {
                                /* if it differs from the last subdevice's erase size, count it */
                                ++num_erase_region;
                                curr_erasesize = subdev[i]->erasesize;
                                if (curr_erasesize > max_erasesize)
                                        max_erasesize = curr_erasesize;
                        }
                } else {
                        /* current subdevice has variable erase size */
                        int j;
                        for (j = 0; j < subdev[i]->numeraseregions; j++) {

                                /* walk the list of erase regions, count any changes */
                                if (subdev[i]->eraseregions[j].erasesize !=
                                    curr_erasesize) {
                                        ++num_erase_region;
                                        curr_erasesize =
                                            subdev[i]->eraseregions[j].
                                            erasesize;
                                        if (curr_erasesize > max_erasesize)
                                                max_erasesize = curr_erasesize;
                                }
                        }
                }
        }

        if (num_erase_region == 1) {
                /*
                 * All subdevices have the same uniform erase size.
                 * This is easy:
                 */
                concat->mtd.erasesize = curr_erasesize;
                concat->mtd.numeraseregions = 0;
        } else {
                uint64_t tmp64;

                /*
                 * erase block size varies across the subdevices: allocate
                 * space to store the data describing the variable erase regions
                 */
                struct mtd_erase_region_info *erase_region_p;
                uint64_t begin, position;

                concat->mtd.erasesize = max_erasesize;
                concat->mtd.numeraseregions = num_erase_region;
                concat->mtd.eraseregions = erase_region_p =
                    kmalloc(num_erase_region *
                            sizeof (struct mtd_erase_region_info), GFP_KERNEL);
                if (!erase_region_p) {
                        kfree(concat);
                        printk
                            ("memory allocation error while creating erase region list"
                             " for device \"%s\"\n", name);
                        return NULL;
                }

                /*
                 * walk the map of the new device once more and fill in
                 * in erase region info:
                 */
                curr_erasesize = subdev[0]->erasesize;
                begin = position = 0;
                for (i = 0; i < num_devs; i++) {
                        if (subdev[i]->numeraseregions == 0) {
                                /* current subdevice has uniform erase size */
                                if (subdev[i]->erasesize != curr_erasesize) {
                                        /*
                                         *  fill in an mtd_erase_region_info structure for the area
                                         *  we have walked so far:
                                         */
                                        erase_region_p->offset = begin;
                                        erase_region_p->erasesize =
                                            curr_erasesize;
                                        tmp64 = position - begin;
                                        do_div(tmp64, curr_erasesize);
                                        erase_region_p->numblocks = tmp64;
                                        begin = position;

                                        curr_erasesize = subdev[i]->erasesize;
                                        ++erase_region_p;
                                }
                                position += subdev[i]->size;
                        } else {
                                /* current subdevice has variable erase size */
                                int j;
                                for (j = 0; j < subdev[i]->numeraseregions; j++) {
                                        /* walk the list of erase regions, count any changes */
                                        if (subdev[i]->eraseregions[j].
                                            erasesize != curr_erasesize) {
                                                erase_region_p->offset = begin;
                                                erase_region_p->erasesize =
                                                    curr_erasesize;
                                                tmp64 = position - begin;
                                                do_div(tmp64, curr_erasesize);
                                                erase_region_p->numblocks = tmp64;
                                                begin = position;

                                                curr_erasesize =
                                                    subdev[i]->eraseregions[j].
                                                    erasesize;
                                                ++erase_region_p;
                                        }
                                        position +=
                                            subdev[i]->eraseregions[j].
                                            numblocks * (uint64_t)curr_erasesize;
                                }
                        }
                }
                /* Now write the final entry */
                erase_region_p->offset = begin;
                erase_region_p->erasesize = curr_erasesize;
                tmp64 = position - begin;
                do_div(tmp64, curr_erasesize);
                erase_region_p->numblocks = tmp64;
        }

        return &concat->mtd;
}

/*
 * This function destroys an MTD object obtained from concat_mtd_devs()
 */

void mtd_concat_destroy(struct mtd_info *mtd)
{
        struct mtd_concat *concat = CONCAT(mtd);
        if (concat->mtd.numeraseregions)
                kfree(concat->mtd.eraseregions);
        kfree(concat);
}

EXPORT_SYMBOL(mtd_concat_create);
EXPORT_SYMBOL(mtd_concat_destroy);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Robert Kaiser <rkaiser@sysgo.de>");
MODULE_DESCRIPTION("Generic support for concatenating of MTD devices");