mtd: sharpslpart: Add sharpslpart partition parser

mtd: sharpslpart: Add sharpslpart partition parser

The Sharp SL Series (Zaurus) PXA handhelds have 16/64/128M of NAND flash
and share the same layout of the first 7M partition, managed by Sharp FTL.

GPL 2.4 sources: http://support.ezaurus.com/developer/source/source_dl.asp

The purpose of this self-contained patch is to add a common parser and
remove the hardcoded sizes in the board files (these devices are not yet
converted to devicetree).
Users will have benefits because the mtdparts= tag will not be necessary
anymore and they will be free to repartition the little sized flash.

The obsolete bootloader can not pass the partitioning info to modern
kernels anymore so it has to be read from flash at known logical addresses.
(see http://www.h5.dion.ne.jp/~rimemoon/zaurus/memo_006.htm )

In kernel, under arch/arm/mach-pxa we have already 8 machines:
MACH_POODLE, MACH_CORGI, MACH_SHEPERD, MACH_HUSKY, MACH_AKITA, MACH_SPITZ,
MACH_BORZOI, MACH_TOSA.
Lost after the 2.4 vendor kernel are MACH_BOXER and MACH_TERRIER.

Almost every model has different factory partitioning: add to this the
units can be repartitioned by users with userspace tools (nandlogical)
and installers for popular (back then) linux distributions.

The Parameter Area in the first (boot) partition extends from 0x00040000 to
0x0007bfff (176k) and contains two copies of the partition table:
...
0x00060000: Partition Info1     16k
0x00064000: Partition Info2     16k
0x00668000: Model               16k
...

The first 7M partition is managed by the Sharp FTL reserving 5% + 1 blocks
for wear-leveling: some blocks are remapped and one layer of translation
(logical to physical) is necessary.

There isn't much documentation about this FTL in the 2.4 sources, just the
MTD methods for reading and writing using logical addresses and the block
management (wear-leveling, use counter).
It seems this FTL was tailored with 16KiB eraesize in mind so to fit one
param block exactly, to have two copies of the partition table on two
blocks.
Later pxa27x devices have same size but 128KiB erasesize and less blocks
(56 vs. 448) but the same schema was adopted, even if the two tables are
now in the same eraseblock.

For the purpose of the MTD parser only the read part of the code was taken.

The NAND drivers that can use this parser are sharpsl.c and tmio_nand.c.

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Richard Weinberger <richard@nod.at>