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Date: Sun, 22 Apr 2012 10:58:44 +0300
From: Shmulik Ladkani <shmulik.ladkani@gmail.com>
To: Brian Norris <computersforpeace@gmail.com>, Mike Dunn
 <mikedunn@newsguy.com>
Subject: Re: [PATCH 1/2] mtd: nand: add OOB argument to NAND {read,
 write}_page interfaces
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On Thu, 19 Apr 2012 15:06:33 -0700 Brian Norris <computersforpeace@gmail.co=
m> wrote:
> On Thu, Apr 19, 2012 at 9:50 AM, Mike Dunn <mikedunn@newsguy.com> wrote:
> > On 04/17/2012 08:44 PM, Brian Norris wrote:
> >
> >> Now, in future revisions of this ASIC, it may be possible to access
> >> OOB via DMA as well, but even if this happens, it doesn't make a lot
> >> of sense on this hardware to *always* pull OOB data.
> >
> >
> > No, it doesn't. In fact, I'm not aware of any code within or on top of =
mtd that
> > does anything with the oob data when a page is read.  If oob is needed,
> > mtd_read_oob() is used.
>=20
> I guess this may not be an issue for page read, but I know one use for
> write_page data+OOB. MLC NAND, for instance, requires that you write
> *once* to a page, so I introduced ioctl(MEMWRITE) which generically
> allows page, OOB, or both to be written. This trickles down to the
> nand_ecc_ctrl.write_page function, I think. There are probably other
> cases that I'm not really thinking of right now.

=46rom MTD user's perspective, mtd_read() and mtd_write() interfaces
do not expose the OOB to the user at all.

OTHO, mtd_read_oob() and mtd_write_oob() allow the user to read/write
either the OOB on its own (NULL 'ops->datbuf'), or the page data along
with its accompanying OOB (non-null 'ops->datbuf' and 'ops->oobbuf').

There are few users of the mtd_read_oob/mtd_write_oob interfaces that
provide a non-null 'ops->datbuf':
- nand_bbt.c
- MEMWRITE mtdchar ioctl
- mtdswap.c
- sm_ftl.c
- yaffs2 (out-of-tree)

Regards,
Shmulik