• Brian Norris's avatar
    mtd: nand: write BBM to OOB even with flash-based BBT · e2414f4c
    Brian Norris authored
    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 incomplete and the
    flash-based table becomes the only source of current bad block
    information. This becomes an obvious problem when, for example:
    
     * 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
    
    So 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. Comments are
    updated, expanded, and/or relocated as necessary.
    
    The new flash-based BBT procedure for marking bad blocks:
     (1) erase the affected block, to allow OOB marker to be written cleanly
     (2) update in-memory BBT
     (3) write bad block marker to OOB area of affected block
     (4) update flash-based BBT
    Note that we retain the first error encountered in (3) or (4), finish the
    procedures, and dump the error in the end.
    
    This should handle power cuts gracefully enough. (1) and (2) are mostly
    harmless (note that (1) will not erase an already-recognized bad block).
    The OOB and BBT may be "out of sync" if we experience power loss bewteen
    (3) and (4), but we can reasonably expect that on next boot, subsequent
    I/O operations will discover that the block should be marked bad again,
    thus re-syncing the OOB and BBT.
    
    Note that this is a change from the previous default flash-based BBT
    behavior. If your system cannot support writing bad block markers to OOB,
    use the new NAND_BBT_NO_OOB_BBM option (in combination with
    NAND_BBT_USE_FLASH and NAND_BBT_NO_OOB).
    Signed-off-by: default avatarBrian Norris <computersforpeace@gmail.com>
    Signed-off-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
    Signed-off-by: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
    e2414f4c
nand_base.c 92.5 KB