[PATCH v2] mtd: nand: write bad block marker even with BBT

[Brian Norris]

Sorry for two e-mails; apparently several addresses I reached were no
longer valid. I'm removing Randy Dunlap and Sukumar Ghorai from the CC
list, and I updated Barry Song and Adrian Hunter's addresses.

Hopefully this can prevent other people from receiving too many
bounces :) Patch description copied below.

On Mon, Dec 19, 2011 at 2:03 PM, Brian Norris
<computersforpeace at gmail.com> wrote:
> Currently, the flash-based BBT implementation writes bad block data only
> to its flash-based table and not to the OOB marker area. Then, as new
> bad blocks are marked over time, the OOB markers become out of date and
> the flash-based table becomes the only source of current bad block
> information. This can be a problem when:
>
>  * bootloader cannot read the flash-based BBT format
>  * BBT is corrupted and the flash must be rescanned for bad
>   blocks; we want to remember bad blocks that were marked from Linux
>
> In an attempt to keep the bad block markers in sync with the flash-based
> BBT, this patch changes the default so that we write bad block markers
> to the proper OOB area on each block in addition to flash-based BBT.
>
> Theoretically, the bad block table and the OOB markers can still get out
> of sync if the system experiences a power cut between writing the BBT to
> flash and writing the OOB marker to a newly-marked bad block. However,
> this is a relatively unlikely event, as new bad blocks shouldn't appear
> frequently.
>
> Note that this is a change from the previous default flash-based BBT
> behavior. If any contributors rely on the old behavior, they are welcome
> to introduce an option flag for it.
>
> Adapted from code by Matthieu Castet.
>
> Signed-off-by: Brian Norris <computersforpeace at gmail.com>

Brian