linux-kernel - Re: [PATCH 00/22 take 3] UBI: Unsorted Block Images

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Message-Id: <1174903360.4182.25.camel@chaos>
Date:	Mon, 26 Mar 2007 12:02:40 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Jörn Engel <joern@...ybastard.org>,
	David Lang <david.lang@...italinsight.com>,
	Matt Mackall <mpm@...enic.com>,
	Josh Boyer <jwboyer@...ux.vnet.ibm.com>,
	Artem Bityutskiy <dedekind@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frank Haverkamp <haver@...t.ibm.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 00/22 take 3] UBI: Unsorted Block Images

On Mon, 2007-03-26 at 10:45 +0100, David Woodhouse wrote:
> On Mon, 2007-03-26 at 03:04 +0200, Jörn Engel wrote:
> > That limitation stems from ECC and ECC is done in software.  Currently
> > everyone and his dog is doing ECC in chunks of 256 bytes on NAND.  So
> > your minimum write size is 256 bytes _if you care about ECC_.  If you
> > don't care, you can write single bits on NAND, just as you can on NOR.
> 
> No, on NAND flash it's a limitation of the hardware. The number of write
> cycles you can perform to a given page is limited. Exceed it and the
> contents of that page become undefined due to leakage, until you next
> erase it. 

Right and you cannot write to random locations in a page. The write
chunks have to be in consecutive order. If you write 0xAA to offset 0,
you cannot rewrite it to 0x00 later without risking corruption.

	tglx


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