/*
 * 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\n");

        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\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_is_nand(mtd)) {
                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     = (loff_t)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 = 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.\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");