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

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Message-ID: <4EEF849B.7030804@freescale.com>
Date:	Mon, 19 Dec 2011 12:38:19 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	<dedekind1@...il.com>
CC:	<shuo.liu@...escale.com>, <dwmw2@...radead.org>,
	<Artem.Bityutskiy@...ia.com>, <linux-mtd@...ts.infradead.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <leoli@...escale.com>
Subject: Re: [PATCH 3/3] mtd/nand : workaround for Freescale FCM to support
 large-page Nand chip

On 12/17/2011 08:35 AM, Artem Bityutskiy wrote:
> On Mon, 2011-12-12 at 15:30 -0600, Scott Wood wrote:
>> On 12/12/2011 03:19 PM, Artem Bityutskiy wrote:
>>> On Mon, 2011-12-12 at 15:15 -0600, Scott Wood wrote:
>>>> NAND chips come from the factory with bad blocks marked at a certain
>>>> offset into each page.  This offset is normally in the OOB area, but
>>>> since we change the layout from "4k data, 128 byte oob" to "2k data, 64
>>>> byte oob, 2k data, 64 byte oob" the marker is no longer in the oob.  On
>>>> first use we need to migrate the markers so that they are still in the oob.
>>>
>>> Ah, I see, thanks. Are you planning to implement in-kernel migration or
>>> use a user-space tool?
>>
>> That's the kind of answer I was hoping to get from Shuo. :-)
>>
>> Most likely is a firmware-based tool, but I'd like there to be some way
>> for the tool to mark that this has happened, so that the Linux driver
>> can refuse to do non-raw accesses to a chip that isn't marked as having
>> been migrated (or at least yell loudly in the log).
>>
>> Speaking of raw accesses, these are currently broken in the eLBC
>> driver... we need some way for the generic layer to tell us what kind of
>> access it is before the transaction starts, not once it wants to read
>> out the buffer (unless we add more hacks to delay the start of a read
>> transaction until first buffer access...).  We'd be better off with a
>> high-level "read page/write page" function that does the whole thing
>> (not just buffer access, but command issuance as well).
> 
> It looks like currently you can re-define chip->read_page, so I guess
> you should rework MTD and make chip->write_page re-definable?

Unless something has changed very recently, there is no chip->read_page
or chip->write_page.  There is chip->ecc.read_page and
chip->ecc.write_page, but they are too low-level.  What we'd need to
replace is a portion of nand_do_read_ops()/nand_do_write_ops().

-Scott

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