From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: linux-mtd@lists.infradead.org,
Laurent Monat <laurent.monat@idquantique.com>,
thorsten.christiansson@idquantique.com,
Enrico Jorns <ejo@pengutronix.de>,
Jason Roberts <jason.e.roberts@intel.com>,
Artem Bityutskiy <artem.bityutskiy@linux.intel.com>,
Dinh Nguyen <dinguyen@kernel.org>,
Marek Vasut <marek.vasut@gmail.com>,
Brian Norris <computersforpeace@gmail.com>,
Graham Moore <grmoore@opensource.altera.com>,
David Woodhouse <dwmw2@infradead.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Chuanxiao Dong <chuanxiao.dong@intel.com>,
Jassi Brar <jaswinder.singh@linaro.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Richard Weinberger <richard@nod.at>,
Cyrille Pitchen <cyrille.pitchen@atmel.com>
Subject: Re: [PATCH v2 10/53] mtd: nand: denali: fix erased page checking
Date: Fri, 24 Mar 2017 09:06:59 +0100 [thread overview]
Message-ID: <20170324090659.76178a37@bbrezillon> (raw)
In-Reply-To: <CAK7LNARt9nagFk_bU0g_+AWk8dv61korDiRiRWTqh2Z-PHsQRw@mail.gmail.com>
On Fri, 24 Mar 2017 11:43:43 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:
> Hi Boris,
>
>
> 2017-03-23 16:56 GMT+09:00 Boris Brezillon <boris.brezillon@free-electrons.com>:
> > On Thu, 23 Mar 2017 14:04:44 +0900
> > Masahiro Yamada <yamada.masahiro@socionext.com> wrote:
> >
> >> Hi Boris,
> >>
> >> 2017-03-23 5:56 GMT+09:00 Boris Brezillon <boris.brezillon@free-electrons.com>:
> >> > 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.
> >>
> >>
> >> OK. How about adding a helper like follows:
> >>
> >> static int denali_check_erased_page(struct mtd_info *mtd,
> >> struct nand_chip *chip, uint8_t *buf)
> >> {
> >> uint8_t *ecc_code = chip->buffers->ecccode;
> >> int ecc_steps = chip->ecc.steps;
> >> int ecc_size = chip->ecc.size;
> >> int ecc_bytes = chip->ecc.bytes;
> >> int i, ret;
> >>
> >> ret = mtd_ooblayout_get_eccbytes(mtd, ecc_code, chip->oob_poi, 0,
> >> chip->ecc.total);
> >> if (ret)
> >> return ret;
> >>
> >> for (i = 0; i < ecc_steps; i++) {
> >> ret = nand_check_erased_ecc_chunk(buf, ecc_size,
> >> ecc_code, ecc_bytes,
> >> NULL, 0,
> >> chip->ecc.strength);
> >> if (ret < 0)
> >> return ret;
> >> buf += ecc_size;
> >> ecc_code += ecc_bytes;
> >> }
> >>
> >> return 0;
> >> }
> >>
> >>
> >>
> >> Then,
> >>
> >> stat = denali_check_erased_page(mtd, chip, buf);
> >> if (stat < 0) {
> >> mtd->ecc_stats.failed++;
> >> /* return 0 for uncorrectable bitflips */
> >> stat = 0;
> >> }
> >
> > What's the point of checking all ECC chunks if only one contains ECC
> > errors? I really recommend to put the nand_check_erased_ecc_chunk()
> > call next to the per-ECC-block correction test.
>
>
> OK. I can fix it for software ECC fixup.
>
>
> What should I do for hardware ECC fixup case?
> http://patchwork.ozlabs.org/patch/742321/
>
>
> If at least one ECC sector fails to correct bit-flips,
> the controller sets INTR__ECC_UNCOR_ERR flag.
>
>
> In this case, we can not know the number of uncorrectable errors.
>
> Possible solutions are:
>
> - Increment ecc_stats.failed only by one (compromised solution)
Let's go for this solution.
>
>
> > Also, mtd->ecc_stats.failed is supposed to be incremented each time an
> > uncorrectable error is detected. In your denali_sw_ecc_fixup()
> > implementation you can detect errors at the ECC chunk level, so you
> > should increment ecc_stats.failed for each failure and not once if at
> > least one chunk is faulty.
>
>
> Yes, I can do this for denali_sw_ecc_fixup().
>
> Can I ask what disadvantage would happen
> if ecc_stats.failed / .corrected is incremented only by one,
> where actually errors happen in multiple sectors.
Reporting wrong stats, which is not such a big deal, but let's try to
keep them correct when we can (the SW ECC fixup case).
next prev parent reply other threads:[~2017-03-24 8:07 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-22 14:07 [PATCH v2 00/53] mtd: nand: denali: 2nd round of Denali NAND IP patch bomb Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 01/53] mtd: nand: allow to set only one of ECC size and ECC strength from DT Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 02/53] mtd: nand: use read_oob() instead of cmdfunc() for bad block check Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 03/53] mtd: nand: denali: remove unused CONFIG option and macros Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 04/53] mtd: nand: denali: remove redundant define of BANK(x) Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 05/53] mtd: nand: denali: remove more unused struct members Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 06/53] mtd: nand: denali: fix comment of denali_nand_info::flash_mem Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 07/53] mtd: nand: denali: consolidate INTR_STATUS__* and INTR_EN__* macros Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 08/53] mtd: nand: denali: introduce capability flag Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 09/53] mtd: nand: denali: use int where no reason to use fixed width variable Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 10/53] mtd: nand: denali: fix erased page checking Masahiro Yamada
2017-03-22 20:36 ` Boris Brezillon
2017-03-23 5:15 ` Masahiro Yamada
2017-03-23 8:03 ` Boris Brezillon
2017-03-22 20:56 ` Boris Brezillon
2017-03-23 5:04 ` Masahiro Yamada
2017-03-23 7:56 ` Boris Brezillon
2017-03-24 2:43 ` Masahiro Yamada
2017-03-24 8:06 ` Boris Brezillon [this message]
2017-03-22 14:07 ` [PATCH v2 11/53] mtd: nand: denali: fix bitflips calculation in handle_ecc() Masahiro Yamada
2017-03-22 20:57 ` Boris Brezillon
2017-03-23 7:02 ` Masahiro Yamada
2017-03-23 8:12 ` Boris Brezillon
2017-03-22 14:07 ` [PATCH v2 12/53] mtd: nand: denali: support HW_ECC_FIXUP capability Masahiro Yamada
2017-03-22 21:09 ` Boris Brezillon
2017-03-23 7:06 ` Masahiro Yamada
2017-03-23 8:16 ` Boris Brezillon
2017-03-22 21:12 ` Boris Brezillon
2017-03-23 7:05 ` Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 13/53] mtd: nand: denali_dt: enable HW_ECC_FIXUP for Altera SOCFPGA variant Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 14/53] mtd: nand: denali: support 64bit capable DMA engine Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 15/53] mtd: nand: denali_dt: remove dma-mask DT property Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 16/53] mtd: nand: denali_dt: use pdev instead of ofdev for platform_device Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 17/53] mtd: nand: denali: allow to override revision number Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 18/53] mtd: nand: denali: use nand_chip to hold frequently accessed data Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 19/53] mtd: nand: denali: call nand_set_flash_node() to set DT node Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 20/53] mtd: nand: denali: do not set mtd->name Masahiro Yamada
2017-03-27 15:31 ` Boris Brezillon
2017-03-28 21:32 ` Masahiro Yamada
2017-03-28 21:40 ` Boris Brezillon
2017-03-29 1:19 ` Masahiro Yamada
2017-03-29 7:19 ` Boris Brezillon
2017-03-29 11:30 ` Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 21/53] mtd: nand: denali: move multi device fixup code to a helper function Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 22/53] mtd: nand: denali: simplify multi device fixup code Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 23/53] mtd: nand: denali: set DEVICES_CONNECTED 1 if not set Masahiro Yamada
2017-03-22 14:07 ` [PATCH v2 24/53] mtd: nand: denali: remove meaningless writes to read-only registers Masahiro Yamada
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