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SubjectRe: [PATCH v5] mtd: rawnand: qcom: erased page bitflips detection
Hi Abhishek,

Abhishek Sahu <absahu@codeaurora.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@codeaurora.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

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