mtd_nandbiterrs.c

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/*
 * Copyright © 2012 NetCommWireless
 * Iwo Mergler <[email protected]>
 *
 * 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.
 */
#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>

#define msg(FMT, VA...) pr_info("mtd_nandbiterrs: "FMT, ##VA)

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;

    msg("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) {
        msg("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)
        msg("write_page\n");

    err = mtd_write(mtd, offset, mtd->writesize, &written, wbuffer);
    if (err || written != mtd->writesize) {
        msg("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)
        msg("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) {
        msg("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)
        msg("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) {
        msg("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)
        msg("verify_page\n");

    for (i = 0; i < mtd->writesize; i++) {
        if (rbuffer[i] != hash(i+seed)) {
            msg("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);
                msg("Inserted biterror @ %u/%u\n", byte, bit);
                return 0;
            }
        }
        byte++;
    }
    msg("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;

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

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

        msg("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));

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

        err = verify_page(0);
        if (err) {
            bitstats[max_corrected] = opno;
            msg("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. */
    msg("Bit error histogram (%d operations total):\n", opno);
    for (i = 0; i < max_corrected; i++)
        msg("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;

    msg("\n");
    msg("==================================================\n");
    msg("MTD device: %d\n", dev);

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

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

    msg("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;

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

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

    msg("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;
    msg("finished successfully.\n");
    msg("==================================================\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");