On Fri, 31 Jul 2015 15:40:13 +0200 Andrea Scian <[email protected]> wrote:
> > Boris, > > Il 31/07/2015 12:32, Boris Brezillon ha scritto: > > Hi Andrea, > > > > Adding Han in Cc. > > > > On Fri, 31 Jul 2015 12:07:21 +0200 > > Andrea Scian <[email protected]> wrote: > > > >> > >> Dear Boris, > >> > >> > >> Il 30/07/2015 19:34, Boris Brezillon ha scritto: > >>> The default NAND read functions are relying on an underlying controller > >>> to correct bitflips, but some of those controller cannot properly fix > >>> bitflips in erased pages. > >>> In case of ECC failures, check if the page of subpage is empty before > >>> reporting an ECC failure. > >> > >> I'm still wondering if chip->ecc.strength is the right threshold. > >> > >> Did you see my comments here [1]? WDYT? > > > > Yes I've read it, and decided to go for ecc->strength as a first > > step (I'm more interested in discussing the approach than the threshold > > value right now ;-)). > > I perfectly understand, that's the reason why I ask if you want to move > to another thread ;-) > > > Anyway, as you pointed out in the thread, writing data on an erased > > page already containing some bitflips might generate even more > > bitflips, so using a different threshold for the erased page check > > makes sense. This threshold should definitely be correlated to the ECC > > strength, but how, that's the question. > > > > How about taking a rather conservative value like 10% of the specified > > ECC strength, and see how it goes. > > Yes, I think that there's no real way to get the right value, other than > feedbacks from on-field testing with various devices. > > I'm also thinking about changing how a NAND page is written on the > device, now that we know that even erased page may have (too many!) > bitflips if they has not been so-freshly erased. > > Read on NAND device is lot's faster that write, so maybe we can: > > a) read the page before write it, check for bitflips on erased area and > write it only if it fit our threshold > > b) read the page after write it and check if the bitflips are lower that > a give value > > In this way: > - we can use ecc_strength as read threshold, because it fits all the > other NAND read > > - we can use "something a bit lower than" mtd->bitflip_threshold on > read-before-write or read-after-write. If we don't do so the block will > be scrubbed next time we read it again (if we are lucky.. if we are > unlucky the block will have bitflip > ecc_strength!): IOW we did a write > that will trigger another erase/write cycle. > > Am I misunderstanding something? Nope, but this implies doing an extra read after each write :-/ -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
