--- /dev/null
+/*
+ * 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.
+ */
+#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");
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