Re: [PATCH v2] mtd: nand: fix lack of oob layout when using no ecc

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Mon, 10 Jul 2017 14:05:19 +0200
Miquel RAYNAL <miquel.raynal@free-electrons.com> wrote:

> Fix nand core lack of OOB layout when:
> - the NFC driver does not provide any OOB layout,
> - ECC operations are disabled (using NAND_ECC_NONE).
> Using this configuration leads to a crash during the probe.
> 
> Add layout functions for small and large pages with mainly free bytes
> plus reserved space for bad block markers.
> 
> Check the configuration and eventually assign this OOB layout in
> nand_scan_tail().
> 
> Bad block markers position was extracted from the existing OOB layouts
> by assigning as free all the bytes marked as ECC.
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
> ---
>  drivers/mtd/nand/nand_base.c | 61 +++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 60 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index c5221795a1e8..98ac54c0a0a7 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -53,7 +53,38 @@ static int nand_get_device(struct mtd_info *mtd, int new_state);
>  static int nand_do_write_oob(struct mtd_info *mtd, loff_t to,
>  			     struct mtd_oob_ops *ops);
>  
> -/* Define default oob placement schemes for large and small page devices */
> +/*
> + * Define default OOB placement schemes for:
> + *   - no ECC or software ECC
> + *   - small or large page devices
> + */
> +static int nand_ooblayout_free_sp_no_ecc(struct mtd_info *mtd, int section,
> +					   struct mtd_oob_region *oobregion)
> +{
> +	if (section > 1)
> +		return -ERANGE;
> +
> +	if (!section) {
> +		if (mtd->oobsize == 16) {
> +			oobregion->offset = 0;
> +			oobregion->length = 4;
> +		} else {
> +			oobregion->offset = 0;
> +			oobregion->length = 5;
> +		}
> +	} else {
> +		oobregion->offset = 6;
> +		oobregion->length = mtd->oobsize - oobregion->offset;
> +	}
> +
> +	return 0;
> +}
> +
> +const struct mtd_ooblayout_ops nand_ooblayout_sp_no_ecc_ops = {
> +	.free = nand_ooblayout_free_sp_no_ecc,
> +};
> +EXPORT_SYMBOL_GPL(nand_ooblayout_sp_no_ecc_ops);
> +
>  static int nand_ooblayout_ecc_sp(struct mtd_info *mtd, int section,
>  				 struct mtd_oob_region *oobregion)
>  {
> @@ -109,6 +140,23 @@ const struct mtd_ooblayout_ops nand_ooblayout_sp_ops = {
>  };
>  EXPORT_SYMBOL_GPL(nand_ooblayout_sp_ops);
>  
> +static int nand_ooblayout_free_lp_no_ecc(struct mtd_info *mtd, int section,
> +					   struct mtd_oob_region *oobregion)
> +{
> +	if (section)
> +		return -ERANGE;
> +
> +	oobregion->offset = 2;
> +	oobregion->length = mtd->oobsize - oobregion->offset;
> +
> +	return 0;
> +}
> +
> +const struct mtd_ooblayout_ops nand_ooblayout_lp_no_ecc_ops = {
> +	.free = nand_ooblayout_free_lp_no_ecc,
> +};
> +EXPORT_SYMBOL_GPL(nand_ooblayout_lp_no_ecc_ops);
> +
>  static int nand_ooblayout_ecc_lp(struct mtd_info *mtd, int section,
>  				 struct mtd_oob_region *oobregion)
>  {
> @@ -4635,6 +4683,17 @@ int nand_scan_tail(struct mtd_info *mtd)
>  	chip->oob_poi = chip->buffers->databuf + mtd->writesize;
>  
>  	/*
> +	 * When using ECC_NONE, ooblayout must only reserve space for bad block
> +	 * markers.
> +	 */
> +	if (!mtd->ooblayout && ecc->mode == NAND_ECC_NONE) {
> +		if (mtd->writesize <= 512)
> +			mtd_set_ooblayout(mtd, &nand_ooblayout_sp_no_ecc_ops);
> +		else
> +			mtd_set_ooblayout(mtd, &nand_ooblayout_lp_no_ecc_ops);
> +	}

Just realized you were breaking existing users of ECC_NONE. Before your
patch, they were using nand_ooblayout_sp_ops for NANDs with 8 or 16 OOB
bytes, and nand_ooblayout_lp_hamming_ops for NANDs with 64 or 128
OOB bytes.

Probably better to put this in the following switch (default case).

> +
> +	/*
>  	 * If no default placement scheme is given, select an appropriate one.
>  	 */
>  	if (!mtd->ooblayout &&