Message-ID: <BLU436-SMTP79A4D637801F08C772536AB86E0@phx.gbl>
From: Bill Pringlemeir <bpringle@sympatico.ca>
To: Brian Norris <computersforpeace@gmail.com>
CC: Stefan Agner <stefan@agner.ch>, bpringlemeir@gmail.com,
        sebastian@breakpoint.cc, robh+dt@kernel.org, pawel.moll@arm.com,
        mark.rutland@arm.com, ijc+devicetree@hellion.org.uk,
        galak@codeaurora.org, shawn.guo@linaro.org, kernel@pengutronix.de,
        boris.brezillon@free-electrons.com, marb@ixxat.de,
        aaron@tastycactus.com, linux-mtd@lists.infradead.org,
        devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, albert.aribaud@3adev.fr,
        klimov.linux@gmail.com, Bill Pringlemeir <bpringlemeir@nbsps.com>
Subject: Re: [PATCH v10 2/5] mtd: nand: vf610_nfc: add hardware BCH-ECC support
Organization: Twits of the world
References: <1438594050-4595-1-git-send-email-stefan@agner.ch>
	<1438594050-4595-3-git-send-email-stefan@agner.ch>
	<ff2e2716578a1ae5f0c4b0e0ca8bbdc3@agner.ch>
	<20150825195411.GJ81844@google.com>
	<07a479863eef4c53ab2ef6ef85321680@agner.ch>
	<20150826213448.GU81844@google.com>
Date: Fri, 28 Aug 2015 17:14:08 -0400
In-Reply-To: <20150826213448.GU81844@google.com> (Brian Norris's message of
	"Wed, 26 Aug 2015 14:34:48 -0700")
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On 26 Aug 2015, computersforpeace@gmail.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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