linux-kernel - Re: [PATCH v10 2/5] mtd: nand: vf610

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Message-ID: <BLU436-SMTP79A4D637801F08C772536AB86E0@phx.gbl>
Date:	Fri, 28 Aug 2015 17:14:08 -0400
From:	Bill Pringlemeir <bpringle@...patico.ca>
To:	Brian Norris <computersforpeace@...il.com>
CC:	Stefan Agner <stefan@...er.ch>, bpringlemeir@...il.com,
	sebastian@...akpoint.cc, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, shawn.guo@...aro.org, kernel@...gutronix.de,
	boris.brezillon@...e-electrons.com, marb@...at.de,
	aaron@...tycactus.com, linux-mtd@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, albert.aribaud@...ev.fr,
	klimov.linux@...il.com, Bill Pringlemeir <bpringlemeir@...ps.com>
Subject: Re: [PATCH v10 2/5] mtd: nand: vf610_nfc: add hardware BCH-ECC support


On 26 Aug 2015, computersforpeace@...il.com wrote:

> On Wed, Aug 26, 2015 at 10:57:38AM -0700, Stefan Agner wrote:
>> When printing the ECC error count on ECC fail when reading an erased
>> NAND flash, the numbers of bit flips (stuck at zero) seem to widely
>> correlate with the number returned by the controller. While it seems
>> to correlate widely, there are exceptions, as discussed in the
>> thread: http://thread.gmane.org/gmane.linux.ports.arm.kernel/295424

>> Maybe this is an artifact of the ECC algorithm we just
>> can't/shouldn't rely on? I am not sure where this originated, I did
>> not found any indication in the reference manual about what that
>> value contains in the error case.

> Doesn't sound too reliable to me. And I'm not sure even if it was
> reliable, that it would provide much value. We have to a lot of
> re-counting anyway, so we might as well just be using our own
> threshold.  Or maybe I'm missing the point.

>> Bill, do you have an idea why we used that value as threshold in
>> early implementations?

>> Otherwise I also think we should just drop the use of this value.

Yes, using this value is not especially useful if we re-read with ECC
disabled to count the bit flips for erased pages.   I think this is what
Stefan has done in the 11th patch set.

-- 
Married men live  longer than single men, but married  men are much more
willing to die - Dilworth
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