linux-kernel - Re: [PATCH 3/3] mtd/nand : workaround for Freescale FCM to support large-page Nand chip

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Date:	Thu, 15 Dec 2011 11:32:40 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	Li Yang <leoli@...escale.com>
CC:	<Artem.Bityutskiy@...ia.com>, <dedekind1@...il.com>,
	<linuxppc-dev@...ts.ozlabs.org>, LiuShuo <b35362@...escale.com>,
	<linux-kernel@...r.kernel.org>, <shuo.liu@...escale.com>,
	<linux-mtd@...ts.infradead.org>, <akpm@...ux-foundation.org>,
	<dwmw2@...radead.org>
Subject: Re: [PATCH 3/3] mtd/nand : workaround for Freescale FCM to support
 large-page Nand chip

On 12/14/2011 10:59 PM, Li Yang wrote:
> The limitation of the proposed bad block marker migration is that you
> need to make sure the migration is done and only done once.  If it is
> done more than once, the factory bad block marker is totally messed
> up.  It requires a complex mechanism to automatically guarantee the
> migration is only done once, and it still won't be 100% safe.
> 
> I would suggest we use a much easier compromise that we form the BBT
> base on the factory bad block marker on first use of the flash, and
> after that the factory bad block marker is dropped.  We just relies on
> the BBT for information about bad blocks.  Although by doing so we
> can't regenerate the BBT again,  as there is mirror for the BBT I
> don't think we have too much risk.

I have corrupted the BBT too often during development (e.g. a bug makes
all accesses fail, so the upper layers decide to mark everything bad) to
be comfortable with this.

Elsewhere in the thread I suggested a way to let the marker be in either
the bbt or in a dedicated block, depending on whether it's a development
situation where the BBT needs to be erasable.

-Scott

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