target/linux/mvebu/patches-3.14/008-nand_warn_weak_ecc_strength.patch

   1 From 67a9ad9b8a6f6ea76ef8fc484ae49970d72d5534 Mon Sep 17 00:00:00 2001
   2 From: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
   3 Date: Wed, 14 May 2014 14:58:06 -0300
   4 Subject: mtd: nand: Warn the user if the selected ECC strength is too weak
   5
   6 This commit makes use of the chip->ecc_strength_ds and chip->ecc_step_ds which
   7 contain the datasheet minimum requested ECC strength to produce a noisy warning
   8 if the configured ECC strength is weaker.
   9
  10 Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
  11 Signed-off-by: Brian Norris <computersforpeace@gmail.com>
  12
  13 --- a/drivers/mtd/nand/nand_base.c
  14 +++ b/drivers/mtd/nand/nand_base.c
  15 @@ -3682,6 +3682,39 @@ int nand_scan_ident(struct mtd_info *mtd
  16  }
  17  EXPORT_SYMBOL(nand_scan_ident);
  18
  19 +/*
  20 + * Check if the chip configuration meet the datasheet requirements.
  21 +
  22 + * If our configuration corrects A bits per B bytes and the minimum
  23 + * required correction level is X bits per Y bytes, then we must ensure
  24 + * both of the following are true:
  25 + *
  26 + * (1) A / B >= X / Y
  27 + * (2) A >= X
  28 + *
  29 + * Requirement (1) ensures we can correct for the required bitflip density.
  30 + * Requirement (2) ensures we can correct even when all bitflips are clumped
  31 + * in the same sector.
  32 + */
  33 +static bool nand_ecc_strength_good(struct mtd_info *mtd)
  34 +{
  35 +       struct nand_chip *chip = mtd->priv;
  36 +       struct nand_ecc_ctrl *ecc = &chip->ecc;
  37 +       int corr, ds_corr;
  38 +
  39 +       if (ecc->size == 0 || chip->ecc_step_ds == 0)
  40 +               /* Not enough information */
  41 +               return true;
  42 +
  43 +       /*
  44 +        * We get the number of corrected bits per page to compare
  45 +        * the correction density.
  46 +        */
  47 +       corr = (mtd->writesize * ecc->strength) / ecc->size;
  48 +       ds_corr = (mtd->writesize * chip->ecc_strength_ds) / chip->ecc_step_ds;
  49 +
  50 +       return corr >= ds_corr && ecc->strength >= chip->ecc_strength_ds;
  51 +}
  52
  53  /**
  54   * nand_scan_tail - [NAND Interface] Scan for the NAND device
  55 @@ -3891,6 +3924,9 @@ int nand_scan_tail(struct mtd_info *mtd)
  56                 ecc->layout->oobavail += ecc->layout->oobfree[i].length;
  57         mtd->oobavail = ecc->layout->oobavail;
  58
  59 +       /* ECC sanity check: warn noisily if it's too weak */
  60 +       WARN_ON(!nand_ecc_strength_good(mtd));
  61 +
  62         /*
  63          * Set the number of read / write steps for one page depending on ECC
  64          * mode.