summaryrefslogtreecommitdiff
path: root/drivers/mtd/mtdconcat.c
blob: 9af840364a74ff849c2aa283b25c0dc6038565a1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
/*
 * MTD device concatenation layer
 *
 * (C) 2002 Robert Kaiser <rkaiser@sysgo.de>
 *
 * NAND support by Christian Gan <cgan@iders.ca>
 *
 * This code is GPL
 *
 * $Id: mtdconcat.c,v 1.11 2005/11/07 11:14:20 gleixner Exp $
 */

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

#include <linux/mtd/mtd.h>
#include <linux/mtd/concat.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 err = -EINVAL;
	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);

		if (err)
			break;

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

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

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_ecc(struct mtd_info *mtd, loff_t from, size_t len,
		size_t * retlen, u_char * buf, u_char * eccbuf,
		struct nand_oobinfo *oobsel)
{
	struct mtd_concat *concat = CONCAT(mtd);
	int err = -EINVAL;
	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;

		if (subdev->read_ecc)
			err = subdev->read_ecc(subdev, from, size,
					       &retsize, buf, eccbuf, oobsel);
		else
			err = -EINVAL;

		if (err)
			break;

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

		err = -EINVAL;
		buf += size;
		if (eccbuf) {
			eccbuf += subdev->oobsize;
			/* in nand.c at least, eccbufs are
			   tagged with 2 (int)eccstatus'; we
			   must account for these */
			eccbuf += 2 * (sizeof (int));
		}
		from = 0;
	}
	return err;
}

static int
concat_write_ecc(struct mtd_info *mtd, loff_t to, size_t len,
		 size_t * retlen, const u_char * buf, u_char * eccbuf,
		 struct nand_oobinfo *oobsel)
{
	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 if (subdev->write_ecc)
			err = subdev->write_ecc(subdev, to, size,
						&retsize, buf, eccbuf, oobsel);
		else
			err = -EINVAL;

		if (err)
			break;

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

		err = -EINVAL;
		buf += size;
		if (eccbuf)
			eccbuf += subdev->oobsize;
		to = 0;
	}
	return err;
}

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

		if (subdev->read_oob)
			err = subdev->read_oob(subdev, from, size,
					       &retsize, buf);
		else
			err = -EINVAL;

		if (err)
			break;

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

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

static int
concat_write_oob(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 if (subdev->write_oob)
			err = subdev->write_oob(subdev, to, size, &retsize,
						buf);
		else
			err = -EINVAL;

		if (err)
			break;

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

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

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;
	u_int32_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 = 0xffffffff;

	/* 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 != 0xffffffff)
				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, size_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];
		size_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, size_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];
		size_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_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 = subdev->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];
		subdev->resume(subdev);
	}
}

/*
 * 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      */
				   char *name)
{				/* name for the new device   */
	int i;
	size_t size;
	struct mtd_concat *concat;
	u_int32_t max_erasesize, curr_erasesize;
	int num_erase_region;

	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 = kmalloc(size, GFP_KERNEL);
	if (!concat) {
		printk
		    ("memory allocation error while creating concatenated device \"%s\"\n",
		     name);
		return NULL;
	}
	memset(concat, 0, size);
	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.oobblock = subdev[0]->oobblock;
	concat->mtd.oobsize = subdev[0]->oobsize;
	concat->mtd.ecctype = subdev[0]->ecctype;
	concat->mtd.eccsize = subdev[0]->eccsize;
	if (subdev[0]->read_ecc)
		concat->mtd.read_ecc = concat_read_ecc;
	if (subdev[0]->write_ecc)
		concat->mtd.write_ecc = concat_write_ecc;
	if (subdev[0]->read_oob)
		concat->mtd.read_oob = concat_read_oob;
	if (subdev[0]->write_oob)
		concat->mtd.write_oob = concat_write_oob;

	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;
		if (concat->mtd.oobblock   !=  subdev[i]->oobblock ||
		    concat->mtd.oobsize    !=  subdev[i]->oobsize ||
		    concat->mtd.ecctype    !=  subdev[i]->ecctype ||
		    concat->mtd.eccsize    !=  subdev[i]->eccsize ||
		    !concat->mtd.read_ecc  != !subdev[i]->read_ecc ||
		    !concat->mtd.write_ecc != !subdev[i]->write_ecc ||
		    !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->num_subdev = num_devs;
	concat->mtd.name = name;

	/*
	 * NOTE: for now, we do not provide any readv()/writev() methods
	 *       because they are messy to implement and they are not
	 *       used to a great extent anyway.
	 */
	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;

	/*
	 * 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 {
		/*
		 * 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;
		u_int32_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;
					erase_region_p->numblocks =
					    (position - begin) / curr_erasesize;
					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;
						erase_region_p->numblocks =
						    (position -
						     begin) / curr_erasesize;
						begin = position;

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

	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");