linux-kernel - Re: [PATCH 0/9] drivers:mtd:UBI: add bakvol module for MLC NAND paired page issue

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Date:	Mon, 28 Sep 2015 09:41:34 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	"Bean Huo 霍斌斌 (beanhuo)" <beanhuo@...ron.com>
Cc:	"dedekind1@...il.com" <dedekind1@...il.com>,
	"adrian.hunter@...el.com" <adrian.hunter@...el.com>,
	"computersforpeace@...il.com" <computersforpeace@...il.com>,
	"baruch@...s.co.il" <baruch@...s.co.il>,
	"asierra@...-inc.com" <asierra@...-inc.com>,
	"guz.fnst@...fujitsu.com" <guz.fnst@...fujitsu.com>,
	"gsi@...x.de" <gsi@...x.de>, "richard@....at" <richard@....at>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"Frank Liu 刘群 (frankliu)" <frankliu@...ron.com>,
	Andrea Scian <rnd4@...e-tech.it>,
	"Peter Pan 潘柏宏 (peterpan)" <peterpan@...ron.com>,
	"Karl Zhang 张双锣 (karlzhang)" 
	<karlzhang@...ron.com>,
	Iwo Mergler <Iwo.Mergler@...commwireless.com>,
	"Jeff Lauruhn (jlauruhn)" <jlauruhn@...ron.com>,
	Stefan Roese <sr@...x.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/9] drivers:mtd:UBI: add bakvol module for MLC NAND
 paired page issue

Hi Bean,

Next time you send a patch series, could send all the patches in reply
to the cover letter?

On Mon, 28 Sep 2015 07:02:35 +0000
Bean Huo 霍斌斌 (beanhuo) <beanhuo@...ron.com> wrote:

> Hello,
> 
> This series aims at adding a bakvol module for MLC NAND paired page
> Power loss protection.
> MLC NAND paired page power loss is a known issue so far, MLC NAND pages are
> coupled in a sense that if you cut power while writing to a page, you corrupt not only
> this page, but also one of the previous pages which is paired with the current one.
> Currently, there is no a perfect solution for this. 
> This paired page solution is based on NAND multiple plane program feature. For this
> Patch, only used dual plane page program, means two different plane pages can
> Be programmed together at the same time.
> Dual plane page program only implements in backup operation. Only lower page data
> Be duplicated and back up into a internal log volume by dual plane program method.

Hm, I'm not very fond of the idea, especially because of the complexity
caused by dual plane program operations (you can't take a random block
to write your backup on it, which means WL is complexified too), and
the fact that you're duplicating data (thus introducing a performance
penalty and storage overhead).

> 
> This patch has been testing on Micron 70s/80s/90s MLC NAND.
> Of course there are some places needed to be improved and simplified.
> 
> Any suggestion and comments welcomed.

Sure, I'll try to review it soon.

Thanks for submitting those patches.

Best Regards,

Boris

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