/*
   * 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>
  #include "mtd_test.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;
  }
  
  /* Writes wbuffer to page */
  static int write_page(int log)
  {
  	if (log)
  		pr_info("write_page
  ");
  
  	return mtdtest_write(mtd, offset, mtd->writesize, wbuffer);
  }
  
  /* 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
  ");
  
  	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)
  ", 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
  ");
  
  	/* 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
  ", (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
  ");
  
  	for (i = 0; i < mtd->writesize; i++) {
  		if (rbuffer[i] != hash(i+seed)) {
  			pr_err("Error: page offset %u, expected %02x, got %02x
  ",
  				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
  ", byte, bit);
  				return 0;
  			}
  		}
  		byte++;
  	}
  	pr_err("biterror: Failed to find a '1' bit
  ");
  	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
  ");
  
  	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
  ", err);
  		if (err < 0) {
  			pr_err("After %d biterrors per subpage, read reported error %d
  ",
  				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
  ");
  			goto exit;
  		}
  
  		pr_info("Successfully corrected %d bit errors per subpage
  ",
  			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
  ");
  
  	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
  ");
  				err = -EIO;
  				break;
  			}
  			bitstats[err]++;
  			if (err > max_corrected) {
  				max_corrected = err;
  				pr_info("Read reported %d corrected bit errors
  ",
  					err);
  			}
  		} else { /* err < 0 */
  			pr_info("Read reported error %d
  ", 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
  ");
  			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):
  ", opno);
  	for (i = 0; i < max_corrected; i++)
  		pr_info("Page reads with %3d corrected bit errors: %d
  ",
  			i, bitstats[i]);
  
  exit:
  	return err;
  }
  
  static int __init mtd_nandbiterrs_init(void)
  {
  	int err = 0;
  
  	printk("
  ");
  	printk(KERN_INFO "==================================================
  ");
  	pr_info("MTD device: %d
  ", dev);
  
  	mtd = get_mtd_device(NULL, dev);
  	if (IS_ERR(mtd)) {
  		err = PTR_ERR(mtd);
  		pr_err("error: cannot get MTD device
  ");
  		goto exit_mtddev;
  	}
  
  	if (!mtd_type_is_nand(mtd)) {
  		pr_info("this test requires NAND flash
  ");
  		err = -ENODEV;
  		goto exit_nand;
  	}
  
  	pr_info("MTD device size %llu, eraseblock=%u, page=%u, oob=%u
  ",
  		(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
  ", subcount, subsize);
  
  	offset     = page_offset * mtd->writesize;
  	eraseblock = mtd_div_by_eb(offset, mtd);
  
  	pr_info("Using page=%u, offset=%llu, eraseblock=%u
  ",
  		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 = mtdtest_erase_eraseblock(mtd, eraseblock);
  	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 = mtdtest_erase_eraseblock(mtd, eraseblock);
  	if (err)
  		goto exit_error;
  
  	err = -EIO;
  	pr_info("finished successfully.
  ");
  	printk(KERN_INFO "==================================================
  ");
  
  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");