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Date: Tue, 3 Nov 2015 14:38:50 +0100
From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Tim Harvey <tharvey@gateworks.com>
Cc: Richard Weinberger <richard@nod.at>, Elie De Brauwer
 <eliedebrauwer@gmail.com>, Artem Bityutskiy <dedekind1@gmail.com>, Adrian
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 Shijie <shijie.huang@arm.com>, Brian Norris <computersforpeace@gmail.com>
Subject: Re: UBIFS corruption after power cut - possibly unstable bits issue?
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Hi Tim,

On Mon, 2 Nov 2015 12:31:11 -0800
Tim Harvey <tharvey@gateworks.com> wrote:

> On Mon, Nov 2, 2015 at 12:27 PM, Tim Harvey <tharvey@gateworks.com> wrote:
> > [    8.635364] UBIFS (ubi0:0): recovery needed
> > [    8.676203] ubi0 warning: ubi_io_read: error -74 (ECC error) while
> > reading 69632 bytes from PEB 2254:192512, read only 69632 bytes, retry
> > [    8.692460] ubi0 warning: ubi_io_read: error -74 (ECC error) while
> > reading 69632 bytes from PEB 2254:192512, read only 69632 bytes, retry
> > [    8.708741] ubi0 warning: ubi_io_read: error -74 (ECC error) while
> > reading 69632 bytes from PEB 2254:192512, read only 69632 bytes, retry
> > ^^^^ non correctable ecc error on PEB 2254  - I verified that this was
> > not the first time this PEB has been used

I suspect one of the bit in PEB 2254 to be stuck at 0 (even after
erasing the block the bit stays at 0). Have you tried to erase this
block (flash_erase /dev/mtd2 0x23380000 1) and dump it in raw mode
(nanddump -n -l 0x40000 -s 0x23380000 -f /tmp/dump /dev/mtd2)?

> >
> > I've cc'd Huang, Elie, and Brian who were involved in the patch to
> > detect bit-flips in gpmi-nand.c reads - perhaps they have some more
> > ideas. I find it interesting that in one case that patch resolves the
> > issue and in the other it does not.

I posted a slightly reworked version of Huang's patch [1] a while ago
addressing the "account for bitflips in OOB area" problem, but maybe we
could do better (avoid this extra "read in raw mode" step, or use the
generic nand_check_erased_ecc_chunk() function when ECC bytes are
aligned).

Best Regards,

Boris

[1]https://patchwork.ozlabs.org/patch/416543/

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com