linux-kernel - Re: [PATCH v5] mtd: rawnand: qcom: erased page bitflips detection

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Date:   Sun, 8 Jul 2018 23:47:42 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Abhishek Sahu <absahu@...eaurora.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, Andy Gross <andy.gross@...aro.org>,
        Archit Taneja <architt@...eaurora.org>
Subject: Re: [PATCH v5] mtd: rawnand: qcom: erased page bitflips detection

Hi Abhishek,

Abhishek Sahu <absahu@...eaurora.org> wrote on Tue,  3 Jul 2018
17:36:03 +0530:

> NAND parts can have bitflips in an erased page due to the
> process technology used. In this case, QCOM NAND controller
> is not able to identify that page as an erased page.
> Currently the driver calls nand_check_erased_ecc_chunk() for
> identifying the erased pages but this won’t work always since the
> checking is being with ECC engine returned data. In case of
> bitflips, the ECC engine tries to correct the data and then it
> generates the uncorrectable error. Now, this data is not equal to
> original raw data. For erased CW identification, the raw data
> should be read again from NAND device and this
> nand_check_erased_ecc_chunk function() should be called for raw
> data only.
> 
> Now following logic is being added to identify the erased
> codeword bitflips.
> 
> 1. In most of the cases, not all the codewords will have bitflips
>    and only single CW will have bitflips. So, there is no need to
>    read the complete raw page data. The NAND raw read can be
>    scheduled for any CW in page. The NAND controller works on CW
>    basis and it will update the status register after each CW read.
>    Maintain the bitmask for the CW which generated the uncorrectable
>    error.
> 2. Do raw read for all the CW's which generated the uncorrectable
>    error.
> 3. Both DATA and OOB need to be checked for number of 0. The
>    top-level API can be called with only data buf or OOB buf so use
>    chip->databuf if data buf is null and chip->oob_poi if
>    OOB buf is null for copying the raw bytes temporarily.
> 4. For each CW, check the number of 0 in cw_data and usable
>    oob bytes, The bbm and spare (unused) bytes bit flip won’t
>    affect the ECC so don’t check the number of bitflips in this area.
> 
> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
> ---
> * Changes from v4:
> 
>  1. Used for_each_set_bit for determining CW’s which generated
>     uncorrectable errors.
>  2. Introduced cw_data_buf and cw_oob_buf which will have starting
>     buffer address for current codeword and used the same in helper
>     functions.
>  3. Added new line before calling of nand_check_erased_ecc_chunk for
>     better code readability.
> 
> * Changes from v3:
> 
>  1. Major changes in erased codeword detection for
>     raw read function
> 
> * Changes from v2:
>   NONE
> 
> * Changes from v1:
>  1. Minor change in commit message
>  2. invalidate pagebuf if databuf or oob_poi is used
> 
>  drivers/mtd/nand/raw/qcom_nandc.c | 126 +++++++++++++++++++++++++++-----------
>  1 file changed, 89 insertions(+), 37 deletions(-)

Applied to nand/next.

Thanks,
Miquèl