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Date:	Mon, 20 Oct 2014 16:02:52 +1100
From:	Iwo Mergler <Iwo.Mergler@...commwireless.com>
To:	Huang Shijie <shijie8@...il.com>
CC:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Mike Voytovich <mvoytovich@...pal.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Roy Lee <roylee@...pal.com>,
	Brian Norris <computersforpeace@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v3 0/3] mtd: nand: gpmi: add proper raw access support

On Sun, 19 Oct 2014 13:20:38 +1100 Huang Shijie <shijie8@...il.com> wrote:
> On Tue, Oct 14, 2014 at 04:50:27PM +1100, Iwo Mergler wrote:
> > 
> > >
> > > No, it doesn't seem to be correct.
> > > But it's an MLC flash, so you'll most probably need to apply this
> > > patch to nandbiterrs testsuite:
> > >
> > > http://code.bulix.org/f69wuu-87021
> > >
> > > This patch is flashing the block between each bitflip insertion to
> > > avoid multiple write without erasure (which, AFAIK, is not
> > > supported by MLC flashes).
> > 
> > Hi Huang,
> > 
> > 
> > just out of interest, have you tried this on the MLC NAND without
> > the patch?
> > 
> > I'm aware that MLC says you shouldn't write multiple times, but
> > that is with a view towards specified data endurance. I would only
> > expect a few additional bit errors during the test.
> > 
> > Did you try the overwrite test?
> > 
> The following is the test result for overwrite with this MLC patch:
> 
> root@...6qdlsolo:~# insmod mtd_nandbiterrs.ko dev=1 mode=1
> [  762.534714] 
> [  762.536259] ==================================================
> [  762.542115] mtd_nandbiterrs: MTD device: 1
> [  762.546326] mtd_nandbiterrs: MTD device size 16777216,
> 	eraseblock=2097152, page=8192, oob=744
> 	[  762.554937] mtd_nandbiterrs: Device uses 1 subpages of 8192
> 	bytes
> 	[  762.561059] mtd_nandbiterrs: Using page=0, offset=0,
> 	eraseblock=0
> 	[  762.571333] mtd_nandbiterrs: overwrite biterrors test
> 	[  762.576715] mtd_nandbiterrs: write_page
> 	[  762.590448] mtd_nandbiterrs: error: read failed at 0x0
> 	[  762.595650] mtd_nandbiterrs: Read reported error -74
> 	[  762.600625] mtd_nandbiterrs: Bit error histogram (0
> 			operations total):
> 	[  762.608586] mtd_nandbiterrs: finished successfully.
> 	[  762.613501]
> 	==================================================
> 	insmod: ERROR: could not insert module mtd_nandbiterrs.ko:
> 	Input/output error
> 

Thanks. If I read this correctly, this means that writing the same data twice,
already generates more bit errors than the ECC can fix.


Best regards,

Iwo

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