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    SubjectRe: [PATCH v2] mtd: rawnand: denali: set SPARE_AREA_SKIP_BYTES register to 8 if unset
    Hi Masahiro,

    Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Fri, 28 Sep
    2018 13:16:01 +0900:

    > NAND devices need additional data area (OOB) for error correction,
    > but it is also used for Bad Block Marker (BBM). In many cases, the
    > first byte in OOB is used for BBM, but the location actually depends
    > on chip vendors. The NAND controller should preserve the precious
    > BBM to keep track of bad blocks.
    >
    > In Denali IP, the SPARE_AREA_SKIP_BYTES register is used to specify
    > the number of bytes to skip from the start of OOB. The ECC engine
    > will automatically skip the specified number of bytes when it gets
    > access to OOB area.
    >
    > The same value for SPARE_AREA_SKIP_BYTES should be used between
    > firmware and the operating system if you intend to use the NAND
    > device across the control hand-off.
    >
    > In fact, the current denali.c code expects firmware to have already
    > set the SPARE_AREA_SKIP_BYTES register, then reads the value out.
    >
    > If no firmware (or bootloader) has initialized the controller, the
    > register value is zero, which is the default after power-on-reset.
    > In other words, the Linux driver cannot initialize the controller
    > by itself.
    >
    > Some possible solutions are:
    >
    > [1] Add a DT property to specify the skipped bytes in OOB
    > [2] Associate the preferred value with compatible
    > [3] Hard-code the default value in the driver
    >
    > My first attempt was [1], but in the review process, [3] was suggested
    > as a counter-implementation.
    > (https://lore.kernel.org/patchwork/patch/983055/)
    >
    > The default value 8 was chosen to match to the boot ROM of the UniPhier
    > platform. The preferred value may vary by platform. If so, please
    > trade up to a different solution.
    >
    > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
    > ---
    >

    Applied to nand/next.


    Thanks,
    Miquèl

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