Re: JFFS2: file contents in case of data CRC error

[Jamie Lokier <jamie@shareable.org>]

Matt Reimer wrote:
> On Jan 31, 2008 8:54 AM, llandre <r&d2@dave-tech.it> wrote:
> > I have a JFFS2 partition on 32MByte NAND device.
> > When reading a specific file - see below for details - JFFS2 reports a
> > Data CRC error but function nand_correct_data never returns -1, so I
> > assume ECC algorithm is able to correct errors.
> > However the file is not equal to the original one that has been written
> > to NAND. In fact, in the middle of the file, I see a 4-kByte "hole"
> > where all bytes are 0.
> > Anybody can help me about understanding if this is the expected
> > behaviour of JFFS2?
> > Thanks in advance.
> 
> I saw exactly this problem on an s3c2440 board back in October. It
> turned out that the ECC correction code in the s3c2410 driver was
> incorrect in a couple of ways, resulting in corrupt data being passed
> up to JFFS2. I'm not sure, but I think what happened from there is
> that JFFS2 failed to decompress a block and instead of returning an
> error it left the page zeroed. You can use jffs2dump to correlate the
> offset reported in the CRC error with the problematic inode. Check the
> thread "bit flip" in October 2007.

I've seen similar things with cfi_cmdset_0002 on NOR flash, with Linux
2.4.26.  Occasional bit flips on reading flash, resulting in zero
blocks in the read file from JFFS2 - no errors reported to the
application.

I have reason to think our board timings were ever so slightly out of
spec, and haven't seen it in newer board revisions.

-- Jamie