[PATCH] nand: fix wrong default oob layout for small pages using soft ecc

[Boris Brezillon]

On Wed, 5 Jul 2017 09:04:53 +0200
Boris Brezillon <boris.brezillon at free-electrons.com> wrote:

> Hi Miquel,
> 
> On Wed,  5 Jul 2017 08:51:09 +0200
> Miquel Raynal <miquel.raynal at free-electrons.com> wrote:
> 
> > When using soft ecc, if no ooblayout is given, the core automatically
> > uses one of the nand_ooblayout_{sp,lp}*() functions to determine the
> > layout inside the out of band data.
> > 
> > Until kernel version 4.6, struct nand_ecclayout was used for that
> > purpose. During the migration from 4.6 to 4.7, an error shown up in the
> > small page layout, in the case oob section is only 8 bytes long.
> > 
> > The layout was using three bytes (0, 1, 2) for ecc, two bytes (3, 4)
> > as free bytes, one byte (5) for bad block marker and finally
> > two bytes (6, 7) as free bytes, as shown there:
> > 
> > [linux-4.6] drivers/mtd/nand/nand_base.c:52
> > static struct nand_ecclayout nand_oob_8 = {
> > 	.eccbytes = 3,
> > 	.eccpos = {0, 1, 2},
> > 	.oobfree = {
> > 		{.offset = 3,
> > 		 .length = 2},
> > 		{.offset = 6,
> > 		 .length = 2} }
> > };
> > 
> > This fixes the current implementation which is incoherent. It
> > references bit 3 at the same time as an ecc byte and a free byte.
> > 
> > Furthermore, it is clear with the previous implementation that there
> > is only one ecc section with 8 bytes oob sections. We shall return
> > -ERANGE in the nand_ooblayout_ecc_sp() function when asked for the
> > second section.

Applied to nand/fixes.

Thanks,

Boris

> > 
> > Signed-off-by: Miquel Raynal <miquel.raynal at free-electrons.com>  
> 
> Looks good to me. BTW, it looks like a good candidate for stable.
> No need to send a v2, I'll add the following when applying:
> 
> Fixes: 41b207a70d3a ("mtd: nand: implement the default mtd_ooblayout_ops")
> Cc: <stable at vger.kernel.org>
> 
> Thanks,
> 
> Boris
> 
> > ---
> >  drivers/mtd/nand/nand_base.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> > index b1dd12729f19..c5221795a1e8 100644
> > --- a/drivers/mtd/nand/nand_base.c
> > +++ b/drivers/mtd/nand/nand_base.c
> > @@ -65,8 +65,14 @@ static int nand_ooblayout_ecc_sp(struct mtd_info *mtd, int section,
> >  
> >  	if (!section) {
> >  		oobregion->offset = 0;
> > -		oobregion->length = 4;
> > +		if (mtd->oobsize == 16)
> > +			oobregion->length = 4;
> > +		else
> > +			oobregion->length = 3;
> >  	} else {
> > +		if (mtd->oobsize == 8)
> > +			return -ERANGE;
> > +
> >  		oobregion->offset = 6;
> >  		oobregion->length = ecc->total - 4;
> >  	}  
>