drivers/mtd/tests/mtd_nandbiterrs.c - kernel/msm-4.9 - Gitiles

 /*
  * Copyright © 2012 NetCommWireless
  * Iwo Mergler <Iwo.Mergler@netcommwireless.com.au>
  *
  * Test for multi-bit error recovery on a NAND page This mostly tests the
  * ECC controller / driver.
  *
  * There are two test modes:
  *
  *	0 - artificially inserting bit errors until the ECC fails
  *	    This is the default method and fairly quick. It should
  *	    be independent of the quality of the FLASH.
  *
  *	1 - re-writing the same pattern repeatedly until the ECC fails.
  *	    This method relies on the physics of NAND FLASH to eventually
  *	    generate '0' bits if '1' has been written sufficient times.
  *	    Depending on the NAND, the first bit errors will appear after
  *	    1000 or more writes and then will usually snowball, reaching the
  *	    limits of the ECC quickly.
  *
  *	    The test stops after 10000 cycles, should your FLASH be
  *	    exceptionally good and not generate bit errors before that. Try
  *	    a different page in that case.
  *
  * Please note that neither of these tests will significantly 'use up' any
  * FLASH endurance. Only a maximum of two erase operations will be performed.
  *
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 as published by
  * the Free Software Foundation.
  *
  * 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; see the file COPYING. If not, write to the Free Software
  * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  */

 #define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt

 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/mtd/mtd.h>
 #include <linux/err.h>
 #include <linux/mtd/nand.h>
 #include <linux/slab.h>

 static int dev;
 module_param(dev, int, S_IRUGO);
 MODULE_PARM_DESC(dev, "MTD device number to use");

 static unsigned page_offset;
 module_param(page_offset, uint, S_IRUGO);
 MODULE_PARM_DESC(page_offset, "Page number relative to dev start");

 static unsigned seed;
 module_param(seed, uint, S_IRUGO);
 MODULE_PARM_DESC(seed, "Random seed");

 static int mode;
 module_param(mode, int, S_IRUGO);
 MODULE_PARM_DESC(mode, "0=incremental errors, 1=overwrite test");

 static unsigned max_overwrite = 10000;

 static loff_t   offset;     /* Offset of the page we're using. */
 static unsigned eraseblock; /* Eraseblock number for our page. */

 /* We assume that the ECC can correct up to a certain number
  * of biterrors per subpage. */
 static unsigned subsize;  /* Size of subpages */
 static unsigned subcount; /* Number of subpages per page */

 static struct mtd_info *mtd;   /* MTD device */

 static uint8_t *wbuffer; /* One page write / compare buffer */
 static uint8_t *rbuffer; /* One page read buffer */

 /* 'random' bytes from known offsets */
 static uint8_t hash(unsigned offset)
 {
 	unsigned v = offset;
 	unsigned char c;
 	v ^= 0x7f7edfd3;
 	v = v ^ (v >> 3);
 	v = v ^ (v >> 5);
 	v = v ^ (v >> 13);
 	c = v & 0xFF;
 	/* Reverse bits of result. */
 	c = (c & 0x0F) << 4 | (c & 0xF0) >> 4;
 	c = (c & 0x33) << 2 | (c & 0xCC) >> 2;
 	c = (c & 0x55) << 1 | (c & 0xAA) >> 1;
 	return c;
 }

 static int erase_block(void)
 {
 	int err;
 	struct erase_info ei;
 	loff_t addr = eraseblock * mtd->erasesize;

 	pr_info("erase_block\n");

 	memset(&ei, 0, sizeof(struct erase_info));
 	ei.mtd  = mtd;
 	ei.addr = addr;
 	ei.len  = mtd->erasesize;

 	err = mtd_erase(mtd, &ei);
 	if (err || ei.state == MTD_ERASE_FAILED) {
 		pr_err("error %d while erasing\n", err);
 		if (!err)
 			err = -EIO;
 		return err;
 	}

 	return 0;
 }

 /* Writes wbuffer to page */
 static int write_page(int log)
 {
 	int err = 0;
 	size_t written;

 	if (log)
 		pr_info("write_page\n");

 	err = mtd_write(mtd, offset, mtd->writesize, &written, wbuffer);
 	if (err || written != mtd->writesize) {
 		pr_err("error: write failed at %#llx\n", (long long)offset);
 		if (!err)
 			err = -EIO;
 	}

 	return err;
 }

 /* Re-writes the data area while leaving the OOB alone. */
 static int rewrite_page(int log)
 {
 	int err = 0;
 	struct mtd_oob_ops ops;

 	if (log)
 		pr_info("rewrite page\n");

 	ops.mode      = MTD_OPS_RAW; /* No ECC */
 	ops.len       = mtd->writesize;
 	ops.retlen    = 0;
 	ops.ooblen    = 0;
 	ops.oobretlen = 0;
 	ops.ooboffs   = 0;
 	ops.datbuf    = wbuffer;
 	ops.oobbuf    = NULL;

 	err = mtd_write_oob(mtd, offset, &ops);
 	if (err || ops.retlen != mtd->writesize) {
 		pr_err("error: write_oob failed (%d)\n", err);
 		if (!err)
 			err = -EIO;
 	}

 	return err;
 }

 /* Reads page into rbuffer. Returns number of corrected bit errors (>=0)
  * or error (<0) */
 static int read_page(int log)
 {
 	int err = 0;
 	size_t read;
 	struct mtd_ecc_stats oldstats;

 	if (log)
 		pr_info("read_page\n");

 	/* Saving last mtd stats */
 	memcpy(&oldstats, &mtd->ecc_stats, sizeof(oldstats));

 	err = mtd_read(mtd, offset, mtd->writesize, &read, rbuffer);
 	if (err == -EUCLEAN)
 		err = mtd->ecc_stats.corrected - oldstats.corrected;

 	if (err < 0 || read != mtd->writesize) {
 		pr_err("error: read failed at %#llx\n", (long long)offset);
 		if (err >= 0)
 			err = -EIO;
 	}

 	return err;
 }

 /* Verifies rbuffer against random sequence */
 static int verify_page(int log)
 {
 	unsigned i, errs = 0;

 	if (log)
 		pr_info("verify_page\n");

 	for (i = 0; i < mtd->writesize; i++) {
 		if (rbuffer[i] != hash(i+seed)) {
 			pr_err("Error: page offset %u, expected %02x, got %02x\n",
 				i, hash(i+seed), rbuffer[i]);
 			errs++;
 		}
 	}

 	if (errs)
 		return -EIO;
 	else
 		return 0;
 }

 #define CBIT(v, n) ((v) & (1 << (n)))
 #define BCLR(v, n) ((v) = (v) & ~(1 << (n)))

 /* Finds the first '1' bit in wbuffer starting at offset 'byte'
  * and sets it to '0'. */
 static int insert_biterror(unsigned byte)
 {
 	int bit;

 	while (byte < mtd->writesize) {
 		for (bit = 7; bit >= 0; bit--) {
 			if (CBIT(wbuffer[byte], bit)) {
 				BCLR(wbuffer[byte], bit);
 				pr_info("Inserted biterror @ %u/%u\n", byte, bit);
 				return 0;
 			}
 		}
 		byte++;
 	}
 	pr_err("biterror: Failed to find a '1' bit\n");
 	return -EIO;
 }

 /* Writes 'random' data to page and then introduces deliberate bit
  * errors into the page, while verifying each step. */
 static int incremental_errors_test(void)
 {
 	int err = 0;
 	unsigned i;
 	unsigned errs_per_subpage = 0;

 	pr_info("incremental biterrors test\n");

 	for (i = 0; i < mtd->writesize; i++)
 		wbuffer[i] = hash(i+seed);

 	err = write_page(1);
 	if (err)
 		goto exit;

 	while (1) {

 		err = rewrite_page(1);
 		if (err)
 			goto exit;

 		err = read_page(1);
 		if (err > 0)
 			pr_info("Read reported %d corrected bit errors\n", err);
 		if (err < 0) {
 			pr_err("After %d biterrors per subpage, read reported error %d\n",
 				errs_per_subpage, err);
 			err = 0;
 			goto exit;
 		}

 		err = verify_page(1);
 		if (err) {
 			pr_err("ECC failure, read data is incorrect despite read success\n");
 			goto exit;
 		}

 		pr_info("Successfully corrected %d bit errors per subpage\n",
 			errs_per_subpage);

 		for (i = 0; i < subcount; i++) {
 			err = insert_biterror(i * subsize);
 			if (err < 0)
 				goto exit;
 		}
 		errs_per_subpage++;
 	}

 exit:
 	return err;
 }


 /* Writes 'random' data to page and then re-writes that same data repeatedly.
    This eventually develops bit errors (bits written as '1' will slowly become
    '0'), which are corrected as far as the ECC is capable of. */
 static int overwrite_test(void)
 {
 	int err = 0;
 	unsigned i;
 	unsigned max_corrected = 0;
 	unsigned opno = 0;
 	/* We don't expect more than this many correctable bit errors per
 	 * page. */
 	#define MAXBITS 512
 	static unsigned bitstats[MAXBITS]; /* bit error histogram. */

 	memset(bitstats, 0, sizeof(bitstats));

 	pr_info("overwrite biterrors test\n");

 	for (i = 0; i < mtd->writesize; i++)
 		wbuffer[i] = hash(i+seed);

 	err = write_page(1);
 	if (err)
 		goto exit;

 	while (opno < max_overwrite) {

 		err = rewrite_page(0);
 		if (err)
 			break;

 		err = read_page(0);
 		if (err >= 0) {
 			if (err >= MAXBITS) {
 				pr_info("Implausible number of bit errors corrected\n");
 				err = -EIO;
 				break;
 			}
 			bitstats[err]++;
 			if (err > max_corrected) {
 				max_corrected = err;
 				pr_info("Read reported %d corrected bit errors\n",
 					err);
 			}
 		} else { /* err < 0 */
 			pr_info("Read reported error %d\n", err);
 			err = 0;
 			break;
 		}

 		err = verify_page(0);
 		if (err) {
 			bitstats[max_corrected] = opno;
 			pr_info("ECC failure, read data is incorrect despite read success\n");
 			break;
 		}

 		opno++;
 	}

 	/* At this point bitstats[0] contains the number of ops with no bit
 	 * errors, bitstats[1] the number of ops with 1 bit error, etc. */
 	pr_info("Bit error histogram (%d operations total):\n", opno);
 	for (i = 0; i < max_corrected; i++)
 		pr_info("Page reads with %3d corrected bit errors: %d\n",
 			i, bitstats[i]);

 exit:
 	return err;
 }

 static int __init mtd_nandbiterrs_init(void)
 {
 	int err = 0;

 	printk("\n");
 	printk(KERN_INFO "==================================================\n");
 	pr_info("MTD device: %d\n", dev);

 	mtd = get_mtd_device(NULL, dev);
 	if (IS_ERR(mtd)) {
 		err = PTR_ERR(mtd);
 		pr_err("error: cannot get MTD device\n");
 		goto exit_mtddev;
 	}

 	if (mtd->type != MTD_NANDFLASH) {
 		pr_info("this test requires NAND flash\n");
 		err = -ENODEV;
 		goto exit_nand;
 	}

 	pr_info("MTD device size %llu, eraseblock=%u, page=%u, oob=%u\n",
 		(unsigned long long)mtd->size, mtd->erasesize,
 		mtd->writesize, mtd->oobsize);

 	subsize  = mtd->writesize >> mtd->subpage_sft;
 	subcount = mtd->writesize / subsize;

 	pr_info("Device uses %d subpages of %d bytes\n", subcount, subsize);

 	offset     = page_offset * mtd->writesize;
 	eraseblock = mtd_div_by_eb(offset, mtd);

 	pr_info("Using page=%u, offset=%llu, eraseblock=%u\n",
 		page_offset, offset, eraseblock);

 	wbuffer = kmalloc(mtd->writesize, GFP_KERNEL);
 	if (!wbuffer) {
 		err = -ENOMEM;
 		goto exit_wbuffer;
 	}

 	rbuffer = kmalloc(mtd->writesize, GFP_KERNEL);
 	if (!rbuffer) {
 		err = -ENOMEM;
 		goto exit_rbuffer;
 	}

 	err = erase_block();
 	if (err)
 		goto exit_error;

 	if (mode == 0)
 		err = incremental_errors_test();
 	else
 		err = overwrite_test();

 	if (err)
 		goto exit_error;

 	/* We leave the block un-erased in case of test failure. */
 	err = erase_block();
 	if (err)
 		goto exit_error;

 	err = -EIO;
 	pr_info("finished successfully.\n");
 	printk(KERN_INFO "==================================================\n");

 exit_error:
 	kfree(rbuffer);
 exit_rbuffer:
 	kfree(wbuffer);
 exit_wbuffer:
 	/* Nothing */
 exit_nand:
 	put_mtd_device(mtd);
 exit_mtddev:
 	return err;
 }

 static void __exit mtd_nandbiterrs_exit(void)
 {
 	return;
 }

 module_init(mtd_nandbiterrs_init);
 module_exit(mtd_nandbiterrs_exit);

 MODULE_DESCRIPTION("NAND bit error recovery test");
 MODULE_AUTHOR("Iwo Mergler");
 MODULE_LICENSE("GPL");
	/*
	* Copyright © 2012 NetCommWireless
	* Iwo Mergler <Iwo.Mergler@netcommwireless.com.au>
	*
	* Test for multi-bit error recovery on a NAND page This mostly tests the
	* ECC controller / driver.
	*
	* There are two test modes:
	*
	* 0 - artificially inserting bit errors until the ECC fails
	* This is the default method and fairly quick. It should
	* be independent of the quality of the FLASH.
	*
	* 1 - re-writing the same pattern repeatedly until the ECC fails.
	* This method relies on the physics of NAND FLASH to eventually
	* generate '0' bits if '1' has been written sufficient times.
	* Depending on the NAND, the first bit errors will appear after
	* 1000 or more writes and then will usually snowball, reaching the
	* limits of the ECC quickly.
	*
	* The test stops after 10000 cycles, should your FLASH be
	* exceptionally good and not generate bit errors before that. Try
	* a different page in that case.
	*
	* Please note that neither of these tests will significantly 'use up' any
	* FLASH endurance. Only a maximum of two erase operations will be performed.
	*
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 as published by
	* the Free Software Foundation.
	*
	* 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; see the file COPYING. If not, write to the Free Software
	* Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/init.h>
	#include <linux/module.h>
	#include <linux/moduleparam.h>
	#include <linux/mtd/mtd.h>
	#include <linux/err.h>
	#include <linux/mtd/nand.h>
	#include <linux/slab.h>

	static int dev;
	module_param(dev, int, S_IRUGO);
	MODULE_PARM_DESC(dev, "MTD device number to use");

	static unsigned page_offset;
	module_param(page_offset, uint, S_IRUGO);
	MODULE_PARM_DESC(page_offset, "Page number relative to dev start");

	static unsigned seed;
	module_param(seed, uint, S_IRUGO);
	MODULE_PARM_DESC(seed, "Random seed");

	static int mode;
	module_param(mode, int, S_IRUGO);
	MODULE_PARM_DESC(mode, "0=incremental errors, 1=overwrite test");

	static unsigned max_overwrite = 10000;

	static loff_t offset; /* Offset of the page we're using. */
	static unsigned eraseblock; /* Eraseblock number for our page. */

	/* We assume that the ECC can correct up to a certain number
	* of biterrors per subpage. */
	static unsigned subsize; /* Size of subpages */
	static unsigned subcount; /* Number of subpages per page */

	static struct mtd_info mtd; / MTD device */

	static uint8_t wbuffer; / One page write / compare buffer */
	static uint8_t rbuffer; / One page read buffer */

	/* 'random' bytes from known offsets */
	static uint8_t hash(unsigned offset)
	{
	unsigned v = offset;
	unsigned char c;
	v ^= 0x7f7edfd3;
	v = v ^ (v >> 3);
	v = v ^ (v >> 5);
	v = v ^ (v >> 13);
	c = v & 0xFF;
	/* Reverse bits of result. */
	c = (c & 0x0F) << 4 \| (c & 0xF0) >> 4;
	c = (c & 0x33) << 2 \| (c & 0xCC) >> 2;
	c = (c & 0x55) << 1 \| (c & 0xAA) >> 1;
	return c;
	}

	static int erase_block(void)
	{
	int err;
	struct erase_info ei;
	loff_t addr = eraseblock * mtd->erasesize;

	pr_info("erase_block\n");

	memset(&ei, 0, sizeof(struct erase_info));
	ei.mtd = mtd;
	ei.addr = addr;
	ei.len = mtd->erasesize;

	err = mtd_erase(mtd, &ei);
	if (err \|\| ei.state == MTD_ERASE_FAILED) {
	pr_err("error %d while erasing\n", err);
	if (!err)
	err = -EIO;
	return err;
	}

	return 0;
	}

	/* Writes wbuffer to page */
	static int write_page(int log)
	{
	int err = 0;
	size_t written;

	if (log)
	pr_info("write_page\n");

	err = mtd_write(mtd, offset, mtd->writesize, &written, wbuffer);
	if (err \|\| written != mtd->writesize) {
	pr_err("error: write failed at %#llx\n", (long long)offset);
	if (!err)
	err = -EIO;
	}

	return err;
	}

	/* Re-writes the data area while leaving the OOB alone. */
	static int rewrite_page(int log)
	{
	int err = 0;
	struct mtd_oob_ops ops;

	if (log)
	pr_info("rewrite page\n");

	ops.mode = MTD_OPS_RAW; /* No ECC */
	ops.len = mtd->writesize;
	ops.retlen = 0;
	ops.ooblen = 0;
	ops.oobretlen = 0;
	ops.ooboffs = 0;
	ops.datbuf = wbuffer;
	ops.oobbuf = NULL;

	err = mtd_write_oob(mtd, offset, &ops);
	if (err \|\| ops.retlen != mtd->writesize) {
	pr_err("error: write_oob failed (%d)\n", err);
	if (!err)
	err = -EIO;
	}

	return err;
	}

	/* Reads page into rbuffer. Returns number of corrected bit errors (>=0)
	* or error (<0) */
	static int read_page(int log)
	{
	int err = 0;
	size_t read;
	struct mtd_ecc_stats oldstats;

	if (log)
	pr_info("read_page\n");

	/* Saving last mtd stats */
	memcpy(&oldstats, &mtd->ecc_stats, sizeof(oldstats));

	err = mtd_read(mtd, offset, mtd->writesize, &read, rbuffer);
	if (err == -EUCLEAN)
	err = mtd->ecc_stats.corrected - oldstats.corrected;

	if (err < 0 \|\| read != mtd->writesize) {
	pr_err("error: read failed at %#llx\n", (long long)offset);
	if (err >= 0)
	err = -EIO;
	}

	return err;
	}

	/* Verifies rbuffer against random sequence */
	static int verify_page(int log)
	{
	unsigned i, errs = 0;

	if (log)
	pr_info("verify_page\n");

	for (i = 0; i < mtd->writesize; i++) {
	if (rbuffer[i] != hash(i+seed)) {
	pr_err("Error: page offset %u, expected %02x, got %02x\n",
	i, hash(i+seed), rbuffer[i]);
	errs++;
	}
	}

	if (errs)
	return -EIO;
	else
	return 0;
	}

	#define CBIT(v, n) ((v) & (1 << (n)))
	#define BCLR(v, n) ((v) = (v) & ~(1 << (n)))

	/* Finds the first '1' bit in wbuffer starting at offset 'byte'
	* and sets it to '0'. */
	static int insert_biterror(unsigned byte)
	{
	int bit;

	while (byte < mtd->writesize) {
	for (bit = 7; bit >= 0; bit--) {
	if (CBIT(wbuffer[byte], bit)) {
	BCLR(wbuffer[byte], bit);
	pr_info("Inserted biterror @ %u/%u\n", byte, bit);
	return 0;
	}
	}
	byte++;
	}
	pr_err("biterror: Failed to find a '1' bit\n");
	return -EIO;
	}

	/* Writes 'random' data to page and then introduces deliberate bit
	* errors into the page, while verifying each step. */
	static int incremental_errors_test(void)
	{
	int err = 0;
	unsigned i;
	unsigned errs_per_subpage = 0;

	pr_info("incremental biterrors test\n");

	for (i = 0; i < mtd->writesize; i++)
	wbuffer[i] = hash(i+seed);

	err = write_page(1);
	if (err)
	goto exit;

	while (1) {

	err = rewrite_page(1);
	if (err)
	goto exit;

	err = read_page(1);
	if (err > 0)
	pr_info("Read reported %d corrected bit errors\n", err);
	if (err < 0) {
	pr_err("After %d biterrors per subpage, read reported error %d\n",
	errs_per_subpage, err);
	err = 0;
	goto exit;
	}

	err = verify_page(1);
	if (err) {
	pr_err("ECC failure, read data is incorrect despite read success\n");
	goto exit;
	}

	pr_info("Successfully corrected %d bit errors per subpage\n",
	errs_per_subpage);

	for (i = 0; i < subcount; i++) {
	err = insert_biterror(i * subsize);
	if (err < 0)
	goto exit;
	}
	errs_per_subpage++;
	}

	exit:
	return err;
	}


	/* Writes 'random' data to page and then re-writes that same data repeatedly.
	This eventually develops bit errors (bits written as '1' will slowly become
	'0'), which are corrected as far as the ECC is capable of. */
	static int overwrite_test(void)
	{
	int err = 0;
	unsigned i;
	unsigned max_corrected = 0;
	unsigned opno = 0;
	/* We don't expect more than this many correctable bit errors per
	* page. */
	#define MAXBITS 512
	static unsigned bitstats[MAXBITS]; /* bit error histogram. */

	memset(bitstats, 0, sizeof(bitstats));

	pr_info("overwrite biterrors test\n");

	for (i = 0; i < mtd->writesize; i++)
	wbuffer[i] = hash(i+seed);

	err = write_page(1);
	if (err)
	goto exit;

	while (opno < max_overwrite) {

	err = rewrite_page(0);
	if (err)
	break;

	err = read_page(0);
	if (err >= 0) {
	if (err >= MAXBITS) {
	pr_info("Implausible number of bit errors corrected\n");
	err = -EIO;
	break;
	}
	bitstats[err]++;
	if (err > max_corrected) {
	max_corrected = err;
	pr_info("Read reported %d corrected bit errors\n",
	err);
	}
	} else { /* err < 0 */
	pr_info("Read reported error %d\n", err);
	err = 0;
	break;
	}

	err = verify_page(0);
	if (err) {
	bitstats[max_corrected] = opno;
	pr_info("ECC failure, read data is incorrect despite read success\n");
	break;
	}

	opno++;
	}

	/* At this point bitstats[0] contains the number of ops with no bit
	* errors, bitstats[1] the number of ops with 1 bit error, etc. */
	pr_info("Bit error histogram (%d operations total):\n", opno);
	for (i = 0; i < max_corrected; i++)
	pr_info("Page reads with %3d corrected bit errors: %d\n",
	i, bitstats[i]);

	exit:
	return err;
	}

	static int __init mtd_nandbiterrs_init(void)
	{
	int err = 0;

	printk("\n");
	printk(KERN_INFO "==================================================\n");
	pr_info("MTD device: %d\n", dev);

	mtd = get_mtd_device(NULL, dev);
	if (IS_ERR(mtd)) {
	err = PTR_ERR(mtd);
	pr_err("error: cannot get MTD device\n");
	goto exit_mtddev;
	}

	if (mtd->type != MTD_NANDFLASH) {
	pr_info("this test requires NAND flash\n");
	err = -ENODEV;
	goto exit_nand;
	}

	pr_info("MTD device size %llu, eraseblock=%u, page=%u, oob=%u\n",
	(unsigned long long)mtd->size, mtd->erasesize,
	mtd->writesize, mtd->oobsize);

	subsize = mtd->writesize >> mtd->subpage_sft;
	subcount = mtd->writesize / subsize;

	pr_info("Device uses %d subpages of %d bytes\n", subcount, subsize);

	offset = page_offset * mtd->writesize;
	eraseblock = mtd_div_by_eb(offset, mtd);

	pr_info("Using page=%u, offset=%llu, eraseblock=%u\n",
	page_offset, offset, eraseblock);

	wbuffer = kmalloc(mtd->writesize, GFP_KERNEL);
	if (!wbuffer) {
	err = -ENOMEM;
	goto exit_wbuffer;
	}

	rbuffer = kmalloc(mtd->writesize, GFP_KERNEL);
	if (!rbuffer) {
	err = -ENOMEM;
	goto exit_rbuffer;
	}

	err = erase_block();
	if (err)
	goto exit_error;

	if (mode == 0)
	err = incremental_errors_test();
	else
	err = overwrite_test();

	if (err)
	goto exit_error;

	/* We leave the block un-erased in case of test failure. */
	err = erase_block();
	if (err)
	goto exit_error;

	err = -EIO;
	pr_info("finished successfully.\n");
	printk(KERN_INFO "==================================================\n");

	exit_error:
	kfree(rbuffer);
	exit_rbuffer:
	kfree(wbuffer);
	exit_wbuffer:
	/* Nothing */
	exit_nand:
	put_mtd_device(mtd);
	exit_mtddev:
	return err;
	}

	static void __exit mtd_nandbiterrs_exit(void)
	{
	return;
	}

	module_init(mtd_nandbiterrs_init);
	module_exit(mtd_nandbiterrs_exit);

	MODULE_DESCRIPTION("NAND bit error recovery test");
	MODULE_AUTHOR("Iwo Mergler");
	MODULE_LICENSE("GPL");