/*
   * 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.retlen;
  		ops->oobretlen += 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:
  ");
  	for (i = 0; i < num_devs; i++)
  		printk(KERN_NOTICE "(%d): \"%s\"
  ", i, subdev[i]->name);
  	printk(KERN_NOTICE "into device \"%s\"
  ", 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\"
  ",
  		     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->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\"
  ",
  			       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\"
  ",
  				       subdev[i]->name);
  				return NULL;
  			} else
  				/* if writeable attribute differs,
  				   make super device writeable */
  				concat->mtd.flags |=
  				    subdev[i]->flags & MTD_WRITEABLE;
  		}

  		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\"
  ",
  			       subdev[i]->name);
  			return NULL;
  		}
  		concat->subdev[i] = subdev[i];
  
  	}

  	mtd_set_ooblayout(&concat->mtd, subdev[0]->ooblayout);

  	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\"
  ", 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");