mtd: Add MTD concat support to concatenate multiple MTD NOR devices

This patch adds concatenation support to the U-Boot MTD infrastructure.
By enabling CONFIG_MTD_CONCAT this MTD CFI wrapper will concatenate
all found NOR devices into one single MTD device. This can be used by
e.g by UBI to access a partition that spans over multiple NOR chips.

Signed-off-by: Stefan Roese <sr@denx.de>

3 files changed, 886 insertions, 1 deletions

diff --git a/drivers/mtd/Makefile b/drivers/mtd/Makefile
index ed3f91e2a4..19dc02b0c3 100644
--- a/drivers/mtd/Makefile
+++ b/drivers/mtd/Makefile
@@ -26,6 +26,7 @@ include $(TOPDIR)/config.mk
 LIB	:= $(obj)libmtd.a
 
 COBJS-$(CONFIG_MTD_PARTITIONS) += mtdcore.o mtdpart.o
+COBJS-$(CONFIG_MTD_CONCAT) += mtdconcat.o
 COBJS-$(CONFIG_HAS_DATAFLASH) += at45.o
 COBJS-$(CONFIG_FLASH_CFI_DRIVER) += cfi_flash.o
 COBJS-$(CONFIG_FLASH_CFI_MTD) += cfi_mtd.o
diff --git a/drivers/mtd/cfi_mtd.c b/drivers/mtd/cfi_mtd.c
index 4a76917ac3..300517e869 100644
--- a/drivers/mtd/cfi_mtd.c
+++ b/drivers/mtd/cfi_mtd.c
@@ -25,14 +25,19 @@
 
 #include <common.h>
 #include <flash.h>
+#include <malloc.h>
 
 #include <asm/errno.h>
 #include <linux/mtd/mtd.h>
+#include <linux/mtd/concat.h>
 
 extern flash_info_t flash_info[];
 
 static struct mtd_info cfi_mtd_info[CONFIG_SYS_MAX_FLASH_BANKS];
 static char cfi_mtd_names[CONFIG_SYS_MAX_FLASH_BANKS][16];
+#ifdef CONFIG_MTD_CONCAT
+static char c_mtd_name[16];
+#endif
 
 static int cfi_mtd_erase(struct mtd_info *mtd, struct erase_info *instr)
 {
@@ -145,16 +150,68 @@ static int cfi_mtd_unlock(struct mtd_info *mtd, loff_t ofs, size_t len)
 static int cfi_mtd_set_erasesize(struct mtd_info *mtd, flash_info_t *fi)
 {
 	int sect_size = 0;
+	int sect_size_old = 0;
 	int sect;
+	int regions = 0;
+	int numblocks = 0;
+	ulong offset = 0;
+	ulong base_addr = fi->start[0];
 
 	/*
-	 * Select the largest sector size as erasesize (e.g. for UBI)
+	 * First detect the number of eraseregions so that we can allocate
+	 * the array of eraseregions correctly
 	 */
 	for (sect = 0; sect < fi->sector_count; sect++) {
+		if (sect_size_old != flash_sector_size(fi, sect))
+			regions++;
+		sect_size_old = flash_sector_size(fi, sect);
+	}
+
+	mtd->eraseregions = malloc(sizeof(struct mtd_erase_region_info) * regions);
+
+	/*
+	 * Now detect the largest sector and fill the eraseregions
+	 */
+	sect_size_old = 0;
+	regions = 0;
+	for (sect = 0; sect < fi->sector_count; sect++) {
+		if ((sect_size_old != flash_sector_size(fi, sect)) &&
+		    (sect_size_old != 0)) {
+			mtd->eraseregions[regions].offset = offset - base_addr;
+			mtd->eraseregions[regions].erasesize = sect_size_old;
+			mtd->eraseregions[regions].numblocks = numblocks;
+
+			/* Now start counting the next eraseregions */
+			numblocks = 0;
+			regions++;
+		} else {
+			numblocks++;
+		}
+
+		if (sect_size_old != flash_sector_size(fi, sect))
+			offset = fi->start[sect];
+
+		/*
+		 * Select the largest sector size as erasesize (e.g. for UBI)
+		 */
 		if (flash_sector_size(fi, sect) > sect_size)
 			sect_size = flash_sector_size(fi, sect);
+
+		sect_size_old = flash_sector_size(fi, sect);
 	}
 
+	/*
+	 * Set the last region
+	 */
+	mtd->eraseregions[regions].offset = offset - base_addr;
+	mtd->eraseregions[regions].erasesize = sect_size_old;
+	mtd->eraseregions[regions].numblocks = numblocks + 1;
+
+	if (regions)
+		mtd->numeraseregions = regions + 1;
+	else
+		mtd->numeraseregions = 0;
+
 	mtd->erasesize = sect_size;
 
 	return 0;
@@ -165,6 +222,8 @@ int cfi_mtd_init(void)
 	struct mtd_info *mtd;
 	flash_info_t *fi;
 	int error, i;
+	int devices_found = 0;
+	struct mtd_info *mtd_list[CONFIG_SYS_MAX_FLASH_BANKS];
 
 	for (i = 0; i < CONFIG_SYS_MAX_FLASH_BANKS; i++) {
 		fi = &flash_info[i];
@@ -193,7 +252,25 @@ int cfi_mtd_init(void)
 
 		if (add_mtd_device(mtd))
 			return -ENOMEM;
+
+		mtd_list[devices_found++] = mtd;
+	}
+
+#ifdef CONFIG_MTD_CONCAT
+	if (devices_found > 1) {
+		/*
+		 * We detected multiple devices. Concatenate them together.
+		 */
+		sprintf(c_mtd_name, "nor%d", devices_found);
+		mtd = mtd_concat_create(mtd_list, devices_found, c_mtd_name);
+
+		if (mtd == NULL)
+			return -ENXIO;
+
+		if (add_mtd_device(mtd))
+			return -ENOMEM;
 	}
+#endif /* CONFIG_MTD_CONCAT */
 
 	return 0;
 }
diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
new file mode 100644
index 0000000000..fc2270127a
--- /dev/null
+++ b/drivers/mtd/mtdconcat.c
@@ -0,0 +1,807 @@
+/*
+ * MTD device concatenation layer
+ *
+ * (C) 2002 Robert Kaiser <rkaiser@sysgo.de>
+ *
+ * NAND support by Christian Gan <cgan@iders.ca>
+ *
+ * This code is GPL
+ */
+
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/compat.h>
+#include <linux/mtd/concat.h>
+#include <ubi_uboot.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;
+
+	*retlen = 0;
+
+	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 = subdev->read(subdev, from, size, &retsize, buf);
+
+		/* Save information about bitflips! */
+		if (unlikely(err)) {
+			if (err == -EBADMSG) {
+				mtd->ecc_stats.failed++;
+				ret = err;
+			} else if (err == -EUCLEAN) {
+				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;
+
+	if (!(mtd->flags & MTD_WRITEABLE))
+		return -EROFS;
+
+	*retlen = 0;
+
+	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;
+
+		if (!(subdev->flags & MTD_WRITEABLE))
+			err = -EROFS;
+		else
+			err = subdev->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_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 = subdev->read_oob(subdev, from, &devops);
+		ops->retlen += devops.retlen;
+		ops->oobretlen += devops.oobretlen;
+
+		/* Save information about bitflips! */
+		if (unlikely(err)) {
+			if (err == -EBADMSG) {
+				mtd->ecc_stats.failed++;
+				ret = err;
+			} else if (err == -EUCLEAN) {
+				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 = 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 = subdev->write_oob(subdev, to, &devops);
+		ops->retlen += devops.retlen;
+		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)
+{
+	/* Nothing to do here in U-Boot */
+}
+
+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;
+
+	if (!(mtd->flags & MTD_WRITEABLE))
+		return -EROFS;
+
+	if (instr->addr > concat->mtd.size)
+		return -EINVAL;
+
+	if (instr->len + instr->addr > concat->mtd.size)
+		return -EINVAL;
+
+	/*
+	 * 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 (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 ((instr->addr + instr->len) & (erase_regions[i].erasesize -
+						  1))
+			return -EINVAL;
+	}
+
+	instr->fail_addr = MTD_FAIL_ADDR_UNKNOWN;
+
+	/* 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;
+
+		if (!(subdev->flags & MTD_WRITEABLE)) {
+			err = -EROFS;
+			break;
+		}
+		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;
+
+	if ((len + ofs) > mtd->size)
+		return -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 = subdev->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;
+
+	if ((len + ofs) > mtd->size)
+		return -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 = subdev->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];
+		subdev->sync(subdev);
+	}
+}
+
+static int concat_block_isbad(struct mtd_info *mtd, loff_t ofs)
+{
+	struct mtd_concat *concat = CONCAT(mtd);
+	int i, res = 0;
+
+	if (!concat->subdev[0]->block_isbad)
+		return res;
+
+	if (ofs > mtd->size)
+		return -EINVAL;
+
+	for (i = 0; i < concat->num_subdev; i++) {
+		struct mtd_info *subdev = concat->subdev[i];
+
+		if (ofs >= subdev->size) {
+			ofs -= subdev->size;
+			continue;
+		}
+
+		res = subdev->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;
+
+	if (!concat->subdev[0]->block_markbad)
+		return 0;
+
+	if (ofs > mtd->size)
+		return -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 = subdev->block_markbad(subdev, ofs);
+		if (!err)
+			mtd->ecc_stats.badblocks++;
+		break;
+	}
+
+	return err;
+}
+
+/*
+ * 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;
+
+	debug("Concatenating MTD devices:\n");
+	for (i = 0; i < num_devs; i++)
+		debug("(%d): \"%s\"\n", i, subdev[i]->name);
+	debug("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
+	 * incompatibilites 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;
+	concat->mtd.subpage_sft = subdev[0]->subpage_sft;
+	concat->mtd.oobsize = subdev[0]->oobsize;
+	concat->mtd.oobavail = subdev[0]->oobavail;
+	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\"\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;
+		}
+
+		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;
+
+	/*
+	 * 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;
+}