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    SubjectRe: [PATCH v2 07/16] mtd/docg3: add OOB layout to mtdinfo
    On Sun, 2011-11-13 at 14:53 +0200, Artem Bityutskiy wrote:
    > On Sun, 2011-11-13 at 11:18 +0100, Robert Jarzmik wrote:
    > > I personally think this should be provided by the MTD API. A function
    > > is_page_blank(ofs) could tell if the page was written or not. Now if the
    > > function is NULL, the upper layer (UBIFS, ...) could decide _by itself_ to
    > > assign a free OOB byte to that meaning. But IMHO it's not the drivers duty to
    > > take these decisions to restrict the OOB, let it be done at an upper level.
    > Probably it is a good idea to introduce an mtd_is_page_blank. But it
    > should either work for all flashes or not introduced at all. I do not
    > think upper layers should use OOB at all. And this interface should also
    > work for NOR flash. Probably it should just fall-back to comparing the
    > data with 0xFF if the driver cannot offer anything special.

    We *tried* comparing with 0xFF in JFFS2 and found that it wasn't good
    enough (it could be *mostly* erased before a powerfail but not
    completely, so as soon as you start to program it you get a lot of
    bitflips). Hence the cleanmarkers.

    The only way you can treat a page as erased is if you *know* it was
    successfully erased. So I'd be reluctant to introduce a function that
    encourages people to draw inferences they shouldn't.

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