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Date: Mon, 26 Mar 2007 02:01:52 +0200
From: =?utf-8?B?SsO2cm4=?= Engel <joern@lazybastard.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: David Lang <david.lang@digitalinsight.com>,
       Thomas Gleixner <tglx@linutronix.de>, Matt Mackall <mpm@selenic.com>,
       Josh Boyer <jwboyer@linux.vnet.ibm.com>,
       Artem Bityutskiy <dedekind@infradead.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Frank Haverkamp <haver@vnet.ibm.com>,
       Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 00/22 take 3] UBI: Unsorted Block Images
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On Mon, 26 March 2007 00:46:33 +0100, David Woodhouse wrote:
> On Mon, 2007-03-26 at 00:55 +0200, Jörn Engel wrote:
> > > although, since you can flip bits to 1 without requireing an erase you 
> > [ vice versa.  you can flip bits to 0 without erasing. ]
> 
> And on NAND flash you can't just do it in multiple cycles one bit at a
> time. The 'tally' trick isn't viable there.

You can on NAND.  ECC is done in software.  And for a data structure as
simple as the 'tally', foregoing ECC is not a huge problem - most
bitflips are easily detected and the remaining only cause off-by-a-few
on the erase count.

On NOR with transparent (hardware) ECC you can't.

Jörn

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