[Yaffs-archive] RE: yaffs: serious error in yaffs guts

[Christian Gan]

Also,

In yaffs_guts there is no real need to check eccres1 and eccres2 you should
only need to check the return value of nandmtd_ReadChunkFromNand.  The two
extra ints from the NAND MTD are only useful when you are performing
multiple page reads when calling nand_read_ecc, since they will tell you
which of the pages you requested has failed.  But YAFFs only a reads single
page at a time, looking at the return value of nand_read_ecc is enough to
know if the write was successful or if an ecc error has occurred for that
page.  This value is checked in nandmtd_ReadChunkFromNand and it passes on a
YAFFS_OK or YAFFS_FAIL (for any ecc errors) appropriately.

Christian

> -----Original Message-----
> From: Nick Bane [mailto:nick@cecomputing.co.uk]
> Sent: Thursday, February 27, 2003 10:31 AM
> To: yaffs list
> Subject: yaffs: serious error in yaffs guts
>
>
> Charles
>
> A couple of bugs. One serious, one minor.
>
> in yaffs_ReadChunkFromNAND when dev->useNANDECC is true, it is
> assumed that
> readChunkFromNAND fills in the two ecc result integers on the end
> of the oob
> data.
> These are then tested to see if there has been and ecc read
> fail/correction
> by the mtd layer.
>
> The problem with this is that readChunkFromNAND never actually passes the
> ecc correction data back but leaves it in a local variable
> tmpSpare and only
> copies YAFFS_BYTES_PER_SPARE from it.
>
> The serious consequence of this is that all chunk reads are then
> flagged as
> failures and their blocks are marked as needing retiring once the data is
> erased so yaffs nand becomes effectively write-once. The really serious
> consequence of this is that one cannot now distinguish between
> yaffs_retired_blocks and nand_factory_bad_blocks so one has to
> speculatively
> erase the entire device losing the factory erase data (which seems to be
> zero on devices I have seen). Shouldn't we use a value other than 0 for
> yaffs to mark the block as bad (with more than two zero bits) so
> they can be
> distinguished?
>
> The other bug is in testing the ecc correction results in
> yaffs_ReadChunkFromNAND.
> if(nspare.eccres2 || nspare.eccres2)
> Clearly one of them should be eccres1
>
> Nick
>
> -------------------------------------------
> Nick Bane
> Cambridge, UK.
> +44(0)1954 719270
>
>
>
>
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