linux-kernel - Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

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Date:	Tue, 5 Aug 2014 19:15:31 +0300
From:	Grazvydas Ignotas <notasas@...il.com>
To:	Roger Quadros <rogerq@...com>
Cc:	Brian Norris <computersforpeace@...il.com>,
	Tony Lindgren <tony@...mide.com>, Felipe Balbi <balbi@...com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	pekon.gupta@...il.com, artem.bityutskiy@...ux.intel.com,
	dwmw2@...radead.org, jg1.han@...sung.com,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mtd: nand: omap: Revert to using software ECC by default

On Tue, Aug 5, 2014 at 1:11 PM, Roger Quadros <rogerq@...com> wrote:
> For v3.12 and prior, 1-bit Hamming code ECC via software was the
> default choice. Commit c66d039197e4 in v3.13 changed the behaviour
> to use 1-bit Hamming code via Hardware using a different ECC layout
> i.e. (ROM code layout) than what is used by software ECC.
>
> This ECC layout change causes NAND filesystems created in v3.12
> and prior to be unusable in v3.13 and later. So revert back to
> using software ECC by default if an ECC scheme is not explicitely
> specified.
>
> This defect can be observed on the following boards during legacy boot
>
> -omap3beagle
> -omap3touchbook
> -overo
> -am3517crane
> -devkit8000
> -ldp
> -3430sdp

omap3pandora is also using sw ecc, with ubifs. Some time ago I tried
booting mainline (I think it was 3.14) with rootfs on NAND, and while
it did boot and reached a shell, there were lots of ubifs errors, fs
got corrupted and I lost all my data. I used to be able to boot
mainline this way fine sometime ~3.8 release. It's interesting that
3.14 was able to read the data, even with wrong ecc setup.

Do you think it's safe again to boot ubifs created on 3.2 after
applying this series?

-- 
Gražvydas
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