Eric Lee / smarc-uboot

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Commit ceb324a2914487aa517a6c70a06a20b5e3438fda

Authored by Peng Fan
1 parent 8183b60202
Exists in smarc-rel_imx_4.1.15_2.0.0_ga

MLK-12693-1 nand: mxs: fix the bitflips for erased page when uncorrectable error 

This patch is porting from linux:
http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/commit/?h=imx_4.1.15_1.0.0_ga&id=3d42fcece496224fde59f9343763fb2dfc5b0768

"
We may meet the bitflips in reading an erased page(contains all 0xFF),
this may causes the UBIFS corrupt, please see the log from Elie:

-----------------------------------------------------------------
[    3.831323] UBI warning: ubi_io_read: error -74 (ECC error) while reading 16384 bytes from PEB 443:245760, read only 16384 bytes, retry
[    3.845026] UBI warning: ubi_io_read: error -74 (ECC error) while reading 16384 bytes from PEB 443:245760, read only 16384 bytes, retry
[    3.858710] UBI warning: ubi_io_read: error -74 (ECC error) while reading 16384 bytes from PEB 443:245760, read only 16384 bytes, retry
[    3.872408] UBI error: ubi_io_read: error -74 (ECC error) while reading 16384 bytes from PEB 443:245760, read 16384 bytes
...
[    4.011529] UBIFS error (pid 36): ubifs_recover_leb: corrupt empty space LEB 27:237568, corruption starts at 9815
[    4.021897] UBIFS error (pid 36): ubifs_scanned_corruption: corruption at LEB 27:247383
[    4.030000] UBIFS error (pid 36): ubifs_scanned_corruption: first 6569 bytes from LEB 27:247383
-----------------------------------------------------------------

This patch does a check for the uncorrectable failure in the following steps:

   [0] set the threshold.
       The threshold is set based on the truth:
       "A single 0 bit will lead to gf_len(13 or 14) bits 0 after the BCH
        do the ECC."

        For the sake of safe, we will set the threshold with half the gf_len, and
        do not make it bigger the ECC strength.

   [1] count the bitflips of the current ECC chunk, assume it is N.

   [2] if the (N <= threshold) is true, we continue to read out the page with
       ECC disabled. and we count the bitflips again, assume it is N2.
       (We read out the whole page, not just a chunk, this makes the check
        more strictly, and make the code more simple.)

   [3] if the (N2 <= threshold) is true again, we can regard this is a erased
       page. This is because a real erased page is full of 0xFF(maybe also has
       several bitflips), while a page contains the 0xFF data will definitely
       has many bitflips in the ECC parity areas.

   [4] if the [3] fails, we can regard this is a page filled with the '0xFF'
       data.
"

Signed-off-by: Peng Fan <peng.fan@nxp.com>

Showing 1 changed file with 44 additions and 0 deletions Side-by-side Diff

drivers/mtd/nand/mxs_nand.c
Diff comments   View file @ ceb324a
... ... @@ -640,6 +640,45 @@
640 640 return buf;
641 641 }
642 642  
  643 +static bool mxs_nand_erased_page(struct mtd_info *mtd, struct nand_chip *nand,
  644 + uint8_t *buf, int chunk, int page)
  645 +{
  646 + int gf_len = galois_field;
  647 + unsigned int flip_bits = 0, flip_bits_noecc = 0;
  648 + unsigned int threshold;
  649 + unsigned int ecc_chunkn_size = MXS_NAND_CHUNK_DATA_CHUNK_SIZE;
  650 + unsigned int base = ecc_chunkn_size * chunk;
  651 + uint32_t *dma_buf = (uint32_t *)buf;
  652 + int i;
  653 +
  654 + threshold = gf_len / 2;
  655 + if (threshold > ecc_strength)
  656 + threshold = ecc_strength;
  657 +
  658 + for (i = 0; i < ecc_chunkn_size; i++) {
  659 + flip_bits += hweight8(~buf[base + i]);
  660 + if (flip_bits > threshold)
  661 + return false;
  662 + }
  663 +
  664 + nand->cmdfunc(mtd, NAND_CMD_READ0, 0, page);
  665 + nand->read_buf(mtd, buf, mtd->writesize);
  666 +
  667 + for (i = 0; i < mtd->writesize / 4; i++) {
  668 + flip_bits_noecc += hweight32(~dma_buf[i]);
  669 + if (flip_bits_noecc > threshold)
  670 + return false;
  671 + }
  672 +
  673 + mtd->ecc_stats.corrected += flip_bits;
  674 +
  675 + memset(buf, 0xff, mtd->writesize);
  676 +
  677 + printf("The page(%d) is an erased page(%d,%d,%d,%d).\n", page, chunk, threshold, flip_bits, flip_bits_noecc);
  678 +
  679 + return true;
  680 +}
  681 +
643 682 /*
644 683 * Read a page from NAND.
645 684 */
... ... @@ -742,6 +781,8 @@
742 781 goto rtn;
743 782 }
744 783  
  784 + mxs_nand_return_dma_descs(nand_info);
  785 +
745 786 /* Invalidate caches */
746 787 mxs_nand_inval_data_buf(nand_info);
747 788  
... ... @@ -758,6 +799,9 @@
758 799 continue;
759 800  
760 801 if (status[i] == 0xfe) {
  802 + if (mxs_nand_erased_page(mtd, nand,
  803 + nand_info->data_buf, i, page))
  804 + break;
761 805 failed++;
762 806 continue;
763 807 }