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Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking

From Boris Brezillon <boris.brezillon@free-electrons.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking
Date 2017-03-22 22:00 +0100
Message-ID <tnVwl-8pR-9@gated-at.bofh.it> (permalink)
References <tnPhf-3Fu-3@gated-at.bofh.it> <tnPhh-3Fu-63@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Wed, 22 Mar 2017 23:07:17 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:
>  		dev_err(denali->dev,
> @@ -1148,12 +1136,15 @@ static int denali_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>  	if (check_erased_page) {
>  		read_oob_data(mtd, chip->oob_poi, denali->page);
>  
> -		/* check ECC failures that may have occurred on erased pages */
> -		if (check_erased_page) {
> -			if (!is_erased(buf, mtd->writesize))
> -				mtd->ecc_stats.failed++;
> -			if (!is_erased(buf, mtd->oobsize))
> -				mtd->ecc_stats.failed++;
> +		stat = nand_check_erased_ecc_chunk(
> +					buf, mtd->writesize,
> +					chip->oob_poi, mtd->oobsize,
> +					NULL, 0,
> +					chip->ecc.strength * chip->ecc.steps);

That's not how it's supposed to be done. Each chunk should be checked
independently. Here is a simple example explaining why this is
important:

Let's consider the following setup:
- 4k pages
- 16bits/1024bytes ECC

With your approach, you turn this into:
- 4k pages
- 64bits/4096bytes ECC

Now suppose you have 32 bitflips in the first 1024 bytes. The real ECC
config is expected to report uncorrectable errors, but your approach
will just report that 32 bits have been fixed, which is wrong.

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Thread

[PATCH v2 00/53] mtd: nand: denali: 2nd round of Denali NAND IP patch bomb Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:20 +0100
  [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:20 +0100
    Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-22 21:40 +0100
      Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-23 08:40 +0100
        Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-23 09:10 +0100
    Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-22 22:00 +0100
      Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-23 08:40 +0100
        Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-23 09:00 +0100
          Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-24 03:50 +0100
            Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-24 09:10 +0100
  [PATCH v2 20/53] mtd: nand: denali: do not set mtd->name Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:20 +0100
    Re: [PATCH v2 20/53] mtd: nand: denali: do not set mtd->name Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-27 17:40 +0200
  [PATCH v2 18/53] mtd: nand: denali: use nand_chip to hold frequently accessed data Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:20 +0100
  [PATCH v2 07/53] mtd: nand: denali: consolidate INTR_STATUS__* and INTR_EN__* macros Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:20 +0100
  [PATCH v2 14/53] mtd: nand: denali: support 64bit capable DMA engine Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:20 +0100
  [PATCH v2 02/53] mtd: nand: use read_oob() instead of cmdfunc() for bad block check Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
  [PATCH v2 06/53] mtd: nand: denali: fix comment of denali_nand_info::flash_mem Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
  [PATCH v2 19/53] mtd: nand: denali: call nand_set_flash_node() to set DT node Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
  [PATCH v2 24/53] mtd: nand: denali: remove meaningless writes to read-only registers Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
  [PATCH v2 03/53] mtd: nand: denali: remove unused CONFIG option and macros Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
  [PATCH v2 01/53] mtd: nand: allow to set only one of ECC size and ECC strength from DT Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
  [PATCH v2 21/53] mtd: nand: denali: move multi device fixup code to a helper function Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
  [PATCH v2 11/53] mtd: nand: denali: fix bitflips calculation in handle_ecc() Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
    Re: [PATCH v2 11/53] mtd: nand: denali: fix bitflips calculation in  handle_ecc() Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-22 22:00 +0100
      Re: [PATCH v2 11/53] mtd: nand: denali: fix bitflips calculation in handle_ecc() Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-23 08:40 +0100
        Re: [PATCH v2 11/53] mtd: nand: denali: fix bitflips calculation in  handle_ecc() Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-23 09:20 +0100
  [PATCH v2 15/53] mtd: nand: denali_dt: remove dma-mask DT property Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
  [PATCH v2 12/53] mtd: nand: denali: support HW_ECC_FIXUP capability Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-22 15:30 +0100
    Re: [PATCH v2 12/53] mtd: nand: denali: support HW_ECC_FIXUP  capability Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-22 22:10 +0100
      Re: [PATCH v2 12/53] mtd: nand: denali: support HW_ECC_FIXUP capability Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-23 08:40 +0100
        Re: [PATCH v2 12/53] mtd: nand: denali: support HW_ECC_FIXUP  capability Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-23 09:30 +0100
    Re: [PATCH v2 12/53] mtd: nand: denali: support HW_ECC_FIXUP  capability Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-22 22:20 +0100
      Re: [PATCH v2 12/53] mtd: nand: denali: support HW_ECC_FIXUP capability Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-23 08:40 +0100

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