Re: should nand driver create ECC for a page after ERASE cmd?

[Brian Norris <computersforpeace@gmail.com>]

On Sun, Dec 21, 2014 at 07:44:26PM +0100, Oleksij Rempel wrote:
> Am 21.12.2014 um 17:28 schrieb Boris Brezillon:
> > Well, actually it depends on your NAND/ECC controller capabilities (but
> > given your discussion with Richard on IRC, I guess you already
> > understood that ;-))
> > 
> > 1) Wiser controllers are generating 0xff ECC bytes for a data chunk
> > (chunk == ECC step size) filled with 0xff. With BCH algorithms this is
> > easily done by XORing the ECC bytes with the appropriate pattern (see
> > soft BCH implementation)
> > 2) Some controller just verify if the data chunk + ECC bytes are all
> > 0xff before passing it to the ECC engine. If they are filled with 0xff
> > the ECC correction is bypassed.
> > This method has one drawback: it does not properly handle bitflips
> > occurring in erased pages (if one bitflip occurs the NAND controller
> > consider the chunk as not empty, and pass it to the BCH engine).
> > 3) The controller does not handle erased pages at all, and in this case
> > you'll have to manually test it (as Ezequiel suggested) when you
> > encounter an ECC error.
> 
> Boris,
> i think your explanation can be placed to mtd web page, some where here :)
> http://www.linux-mtd.infradead.org/doc/general.html#L_mtd_tests

Patches are welcome:

http://www.linux-mtd.infradead.org/faq/general.html#L_mtdwww

Brian