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

[Boris Brezillon]

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.
> 
> 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;
>  	}