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Subject: Re: OOB Location
From: Thomas Gleixner <tglx@linutronix.de>
To: ajain@neomagic.com
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Date: Thu, 28 Sep 2006 02:14:19 +0200
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On Sat, 2006-09-16 at 18:56 +0530, Ajay Jain wrote:
> I have one question regarding JFFS2 on NAND flash. My hardware has a
> NAND flash controller, which does automatic error correction. It needs
> 10 bytes for this, which it stores in the OOB area of each page. JFFS2
> also stores some information in this area, from locations 8-15 for a 512
> page-size NAND flash. Now the issue is that the storage locations as
> used by our hardware and JFFS2 clash. My first hunch is that its a
> quirky hardware. My questions is:

That's supported. JFFS2 puts the cleanmarker into the bytes which are
not used by ECC.

static struct nand_ecclayout rtc_from4_nand_oobinfo = {
	.eccbytes = 32,
	.eccpos = {
		   0, 1, 2, 3, 4, 5, 6, 7,
		   8, 9, 10, 11, 12, 13, 14, 15,
		   16, 17, 18, 19, 20, 21, 22, 23,
		   24, 25, 26, 27, 28, 29, 30, 31},
	.oobfree = {{32, 32}}
};

JFFS2 puts the cleanmarker at offset 32 in OOB.

> Is it possible to use some other location for storing file-system
> information. Is there an option, so that JFFS2 can store this
> information in some other area? If yes, how to use this. I saw the
> 'mkfs.jffs2' help, it does not expose any such option. 

mkfs.jffs2 does not know anything about the OOB usage scheme at all.

	tglx