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Subject: Re: How to write to nand with an image containing oob data,
	including ECC?
From: Artem Bityutskiy <dedekind1@gmail.com>
To: Ricard Wanderlof <ricard.wanderlof@axis.com>
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Date: Tue, 29 Mar 2011 18:42:51 +0300
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Cc: Kelly Anderson <kelly@silka.with-linux.com>,
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On Tue, 2011-03-29 at 17:30 +0200, Ricard Wanderlof wrote:
> Hi,
> 
> In order to test an ECC algorithm (BCH in this case, as I recently posted 
> about), i want to write an image to a nand flash which contains bit 
> errors.
> 
> What I want to do, and I seem to remember doing this in the past, is to 
> dump the whole image, change a single bit, and write it back, including 
> the oob.
> 
> So what I'm doing is
> 
> $ nandwrite -o -n /dev/mtd3 /tmp/mtd3-badimage
> 
> where /tmp/mtd3-badimage contains an image including all oobs for all 
> pages.
> 
> However, this fails saying
> 
> Writing data to block 0 at offset 0x0
> libmtd: error!: cannot write 2048 bytes to mtd3 (eraseblock 0, offset 0)
>          error 22 (Invalid argument)
> nandwrite: error!: /dev/mtd3: MTD write failure
>             error 22 (Invalid argument)
> Data was only partially written due to error
> : Invalid argument
> 
> Using just -o doesn't work because it seems nandwrite writes the oob, but 
> then since it doesn't write the main page in raw mode, the ecc gets 
> overwritten. Strangely enough, the ECC doesn't seem to match the data 
> written, as I get uncorrectable errors when reading back (not just with 
> BCH, but also with the standard mtd built-in algorithm). Perhaps the oob 
> gets written twice, once with my data and once more with the calculated 
> ecc?
> 
> Is this a known bug, or are the some other options I should be using?

Check this bug-report, probably it is about the same. Not sure, I did
not have time to look at this:

http://lists.infradead.org/pipermail/linux-mtd/2011-March/034505.html

would be great if someone just sent a fix :-)

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)