linux-kernel - Re: [PATCH v2 07/16] mtd/docg3: add OOB layout to mtdinfo

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Message-ID: <87ehxchta0.fsf@free.fr>
Date:	Sun, 13 Nov 2011 17:38:31 +0100
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	dedekind1@...il.com, David Woodhouse <dwmw2@...radead.org>
Cc:	Mike Dunn <mikedunn@...sguy.com>, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Ivan Djelic <ivan.djelic@...rot.com>
Subject: Re: [PATCH v2 07/16] mtd/docg3: add OOB layout to mtdinfo

Artem Bityutskiy <dedekind1@...il.com> writes:

> What Robert says is that we probably need an is_page_blank() and let the
> driver implement it optimally, or make MTD fall-back to 0xFFs
> comparison.
>
> This is my understanding.
And that's exactly my point.

And while we're discussing MTD API, I'd like to add another thing I was thinking
of, from a conversation Mike and Ivan had.

They discussed how UBIFS is "intolerant" to bitflips, and marks a block as
"unusable" if one bitflip occured, even if the ECC can fix much more.

What I was thinking is that the MTD oob information which exposes how many ECC
are available should expose as well how many bitflips can be fixed (for example
4 bitflips can be fixed, 5 bitflips can be detected). Then, the read_oob()
function could return back 0 if read was successful, -Exxxx on error, or a
positive number N if N bitflips were fixed.
With this information, upper level could decide from (read_oob() return and
ecc.fixable_bitflips) if a block should be marked as unusable (worn out) or not.

I'd like some feedback on this idea as well.

Cheers.

--
Robert
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