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

[Nick Bane]

Charles/Christian

One problem with Christian's proposal is that it fails to distinguish
between a totally failed read and an error corrected read. If the return
values from readChunkFromNAND can differentiate the two states that may be
helpful in the future.

Nick Bane

----- Original Message -----
From: "Charles Manning" <manningc2@actrix.gen.nz>
To: "Christian Gan" <cgan@iders.ca>; "Nick Bane" <nick@cecomputing.co.uk>;
"yaffs list" <yaffs@toby-churchill.org>
Sent: Thursday, February 27, 2003 9:01 PM
Subject: Re: yaffs: serious error in yaffs guts


> Hi Christian
>
> It is easiest for me if someone using the Linux MTD with NANDECC can test
> this. Otherewise I will have to write a software emulator.
>
> Could you roll this together with Thomas' recent patchs for NANDECC, with
> your proposed ammendments, and I can apply them as a consistent patch set.
>
> Thanx
>
> -- Charles
>
>
> On Fri, 28 Feb 2003 06:27, Christian Gan wrote:
> > 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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>



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