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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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