On Thu, Oct 11, 2007 at 08:44:14PM +0100, Ben Dooks wrote:
> On Thu, Oct 11, 2007 at 10:35:55AM -0400, Ian McDonnell wrote:
> > Ben,
> > 
> > On Thursday 11 October 2007 07:25, Ben Dooks wrote:
> > > I'm working on upgrading a client's kernel from 2.6.10 to
> > > 2.6.22. They are using yaffs to store their configuration
> > > data.
> > >
> > > When I start the 2.6.22 kernel, I get a number of the
> > > following: **>> yaffs chunk 32 was not erased
> > >
> > > If I run 2.6.10 after writing the files from 2.6.22 I get
> > > blocks with ECC errors in them, and the files get corrupted.
> > 
> > The problem is with a change to MTD -- MTD's NAND interface had 
> > an overhaul between 2.6.17 and mid-late 2.6.18. MTD's default 
> > layout of oob data in the NAND page's spare area changed. This 
> > means that yaffs' tag metadata gets scrambled when you jump 
> > between versions of MTD. There are ways to fix this, you can 
> > supply MTD with your own layout policy. Rumage through the mail 
> > archive to find some discussion on the topic.
> > http://aleph1.co.uk/lurker/list/yaffs.en.html
> 
> I didn't find anything relevant to this. I have found one problem,
> if CONFIG_YAFFS_DOES_ECC is set, and the mtd driver has an ECC
> method, then it seems to be using the mtd hardware ECC code during
> reads. The Kconfig help text seems to imply this should override
> anything NAND is up to?
> 
> Even with the hardware ECC disabled, nipping between the two
> kernels is still giving:
> 
> yaffs_ECCCorrect: READ ff,ff,bf WANT ff,ff,ff, DIFF 00,00,40
> 
> The diff value is _always_ 00,00,40 whatever the ECC being read.

With the diff always being this, I belive the mtd oob layout is now
synchronised between the two kernel versions... both kernels can see
the file in question, but the ecc correction causes the file to end
up being 'corrected' when it does not need it. 

I will continue running debug on this, becuase before the debugging
the two ecc genrators where exactly the same file.

-- 
Ben

Q:      What's a light-year?
A:      One-third less calories than a regular year.