mtd: nand: remove multiplied-by-2 block logic

The previous patch makes the following comment obsolete:

	/*
	 * Note that numblocks is 2 * (real numblocks) here, see i+=2
	 * below as it makes shifting and masking less painful
	 */

I don't think it ever could have been "less painful" to have to shift an
extra bit (or 2, or 3) at various points in nand_bbt.c (and even
outside, since we leak our in-memory format). But now it is certainly
more painful, since we have nice macros and functions to retrieve the
relevant portions of the BBT.

This patch removes any points where the block number is
doubled/halved/otherwise-shifted, instead representing the block number
in its most natural form: as the actual block number.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
mtd: nand: eliminate cast

Just make 'res' an int.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
mtd: nand: refactor chip->block_markbad interface

The chip->block_markbad pointer should really only be responsible for
writing a bad block marker for new bad blocks. It should not take care
of BBT-related functionality, nor should it handle bookkeeping of bad
block stats.

This patch refactors the 3 users of the block_markbad interface (plus
the default nand_base implementation) so that the common code is kept in
nand_block_markbad_lowlevel(). It removes some inconsistencies between
the various implementations and should allow for more centralized
improvements in the future.

Because gpmi-nand no longer needs the nand_update_bbt() function, let's
stop exporting it as well.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Huang Shijie <b32955@freescale.com> (for gpmi-nand parts)
mtd: nand: hide in-memory BBT implementation details

nand_base.c shouldn't have to know the implementation details of
nand_bbt's in-memory BBT. Specifically, nand_base shouldn't perform the
bit masking and shifting to isolate a BBT entry.

Instead, just move some of the BBT code into a new nand_markbad_bbt()
interface. This interface allows external users (i.e., nand_base) to
mark a single block as bad in the BBT. Then nand_bbt will take care of
modifying the in-memory BBT and updating the flash-based BBT (if
applicable).

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
mtd: nand: remove NAND_BBT_SCANEMPTY

NAND_BBT_SCANEMPTY is a strange, badly-supported option with omap as its
single remaining user.

NAND_BBT_SCANEMPTY was likely used by accident in omap2[1]. And anyway,
omap2 doesn't scan the chip for bad blocks (courtesy of
NAND_SKIP_BBTSCAN), and so its use of this option is irrelevant.

This patch drops the NAND_BBT_SCANEMPTY option.

[1] http://lists.infradead.org/pipermail/linux-mtd/2012-July/042902.html

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Ivan Djelic <ivan.djelic@parrot.com>