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    SubjectRe: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default
    Hi Gražvydas,

    On 08/05/2014 07:15 PM, Grazvydas Ignotas wrote:
    > On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@ti.com> wrote:
    >> For v3.12 and prior, 1-bit Hamming code ECC via software was the
    >> default choice. Commit c66d039197e4 in v3.13 changed the behaviour
    >> to use 1-bit Hamming code via Hardware using a different ECC layout
    >> i.e. (ROM code layout) than what is used by software ECC.
    >>
    >> This ECC layout change causes NAND filesystems created in v3.12
    >> and prior to be unusable in v3.13 and later. So revert back to
    >> using software ECC by default if an ECC scheme is not explicitely
    >> specified.
    >>
    >> This defect can be observed on the following boards during legacy boot
    >>
    >> -omap3beagle
    >> -omap3touchbook
    >> -overo
    >> -am3517crane
    >> -devkit8000
    >> -ldp
    >> -3430sdp
    >
    > omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
    > booting mainline (I think it was 3.14) with rootfs on NAND, and while
    > it did boot and reached a shell, there were lots of ubifs errors, fs
    > got corrupted and I lost all my data. I used to be able to boot
    > mainline this way fine sometime ~3.8 release. It's interesting that
    > 3.14 was able to read the data, even with wrong ecc setup.

    This is due to another bug introduced in 3.7 by commit 65b97cf6b8deca3ad7a3e00e8316bb89617190fb.
    Because of that bug (i.e. inverted CS_MASK in omap_calculate_ecc), omap_calculate_ecc() always fails with -EINVAL and calculated ECC bytes are always 0. I'll be sending a patch to fix that as well. But that will only affect the cases where OMAP_ECC_HAM1_CODE_HW is used which happened for pandora from 3.13 onwards.

    >
    > Do you think it's safe again to boot ubifs created on 3.2 after
    > applying this series?
    >

    Yes. If you boot pandora using legacy boot (non DT method), it passes 0 for .ecc_opt in pandora_nand_data. This used to mean OMAP_ECC_HAMMING_CODE_DEFAULT which is software ecc. i.e. NAND_ECC_SOFT with default ECC layout. Until the above mentioned commits changed the meaning. We now call that option OMAP_ECC_HAM1_CODE_SW.

    Please let me know if it works for you. Thanks.

    cheers,
    -roger
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