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

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Message-ID: <20070326000149.GE19691@lazybastard.org>
Date:	Mon, 26 Mar 2007 02:01:52 +0200
From:	Jörn Engel <joern@...ybastard.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	David Lang <david.lang@...italinsight.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	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, 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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