mtd: docg3: add fast mode
Docg3 chips can work in 3 modes : normal MLC mode, fast mode and reliable mode. Normally, as docg3 is a MLC chip, it should be configured to work in normal mode. In both normal mode, each page is distinct. This means that writing to page 12 of blocks 14,15 writes only to that page, and reading from page 12 of blocks 14,15 reads only from that page. In reliable and fast modes, pages are coupled by pairs, and are clones one of each other. This means that the available capacity of the chip is halved. Pages are coupled in each block, and page of index 2*n contains the same data as page 2*n+1 of the same block. In fast mode, the reads occur a bit faster, but are a bit less reliable that in normal mode. When reading from page 2*n, the chip reads bytes from both page 2*n and page 2*n+1, makes a logical and for each byte, and returns the result. As programming a page means "clearing bits", even if a bit was not cleared on one page because the flash is worn out, the other page has the bit cleared, and the result of the "AND" gives a correct result. When writing to page 2*n, the chip writes data to both page 2*n and page 2*n+1. Signed-off-by: NRobert Jarzmik <robert.jarzmik@free.fr> Reviewed-by: NIvan Djelic <ivan.djelic@parrot.com> Reviewed-by: NMike Dunn <mikedunn@newsguy.com> Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>
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