linux-kernel - Re: [RFC PATCH 2/2] mtd: nand: use nand_check_erased_ecc

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Message-ID: <20150731123221.34cf601e@bbrezillon>
Date:	Fri, 31 Jul 2015 12:32:21 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Andrea Scian <rnd4@...e-tech.it>
Cc:	linux-mtd@...ts.infradead.org,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-kernel@...r.kernel.org, Han Xu <b45815@...escale.com>
Subject: Re: [RFC PATCH 2/2] mtd: nand: use nand_check_erased_ecc_chunk in
 default ECC read functions

Hi Andrea,

Adding Han in Cc.

On Fri, 31 Jul 2015 12:07:21 +0200
Andrea Scian <rnd4@...e-tech.it> wrote:

> 
> Dear Boris,
> 
> 
> Il 30/07/2015 19:34, Boris Brezillon ha scritto:
> > The default NAND read functions are relying on an underlying controller
> > to correct bitflips, but some of those controller cannot properly fix
> > bitflips in erased pages.
> > In case of ECC failures, check if the page of subpage is empty before
> > reporting an ECC failure.
> 
> I'm still wondering if chip->ecc.strength is the right threshold.
> 
> Did you see my comments here [1]? WDYT?

Yes I've read it, and decided to go for ecc->strength as a first
step (I'm more interested in discussing the approach than the threshold
value right now ;-)).

Anyway, as you pointed out in the thread, writing data on an erased
page already containing some bitflips might generate even more
bitflips, so using a different threshold for the erased page check
makes sense. This threshold should definitely be correlated to the ECC
strength, but how, that's the question.

How about taking a rather conservative value like 10% of the specified
ECC strength, and see how it goes.

> 
> Maybe we can have this discussion in a separate thread, if you want ;-)

No, I think we should keep discussing it in this thread.

Thanks,

Boris

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