Re: [PATCH] mtd: nand: Add support for reading ooblayout from device tree

[Boris Brezillon <boris.brezillon@bootlin.com>]

Hi Paul,

On Fri, 11 May 2018 23:29:12 +0200
Paul Cercueil <paul@crapouillou.net> wrote:

> By specifying the properties "mtd-oob-ecc" and "mtd-oob-free", it is
> now possible to specify from devicetree where the ECC data is located
> inside the OOB region.

Why would we want to do that? I mean, ECC/free regions are ECC
controller dependent (and NAND chip dependent for the OOB size part),
so there's no reason to describe it in the DT. And more importantly,
people are likely to get it wrong.

I'm curious, why do you need that?

Regards,

Boris

> 
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> ---
>  Documentation/devicetree/bindings/mtd/nand.txt |  7 +++++
>  drivers/mtd/nand/raw/nand_base.c               | 42 ++++++++++++++++++++++++++
>  2 files changed, 49 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/nand.txt b/Documentation/devicetree/bindings/mtd/nand.txt
> index 8bb11d809429..118ea92787cb 100644
> --- a/Documentation/devicetree/bindings/mtd/nand.txt
> +++ b/Documentation/devicetree/bindings/mtd/nand.txt
> @@ -45,6 +45,13 @@ Optional NAND chip properties:
>  		     as reliable as possible.
>  - nand-rb: shall contain the native Ready/Busy ids.
>  
> +- nand-oob-ecc: <offset, length> couples of integers, specifying the offset
> +		     and length of the ECC data in the OOB region. There can be more
> +		     than one couple.
> +- nand-oob-free: <offset, length> couples of integers, specifying the offset
> +		     and length of a free-to-use area in the OOB region. There can be
> +		     more than one couple.
> +
>  The ECC strength and ECC step size properties define the correction capability
>  of a controller. Together, they say a controller can correct "{strength} bit
>  errors per {size} bytes".
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index 72f3a89da513..c905531effb0 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -213,6 +213,43 @@ static const struct mtd_ooblayout_ops nand_ooblayout_lp_hamming_ops = {
>  	.free = nand_ooblayout_free_lp_hamming,
>  };
>  
> +static int nand_oob_of(struct device_node *np, int section,
> +		       struct mtd_oob_region *oobregion, const char *prop)
> +{
> +	int ret = of_property_read_u32_index(np, prop,
> +			section * 2, &oobregion->offset);
> +	if (ret == -EOVERFLOW)
> +		return -ERANGE; /* We're done */
> +	if (ret)
> +		return ret;
> +
> +	ret = of_property_read_u32_index(np, prop,
> +			section * 2 + 1, &oobregion->length);
> +	if (ret == -EOVERFLOW)
> +		return -EINVAL; /* We must have an even number of integers */
> +
> +	return ret;
> +}
> +
> +static int nand_ooblayout_ecc_of(struct mtd_info *mtd, int section,
> +				 struct mtd_oob_region *oobregion)
> +{
> +	return nand_oob_of(mtd->dev.of_node, section,
> +			oobregion, "nand-oob-ecc");
> +}
> +
> +static int nand_ooblayout_free_of(struct mtd_info *mtd, int section,
> +				 struct mtd_oob_region *oobregion)
> +{
> +	return nand_oob_of(mtd->dev.of_node, section,
> +			oobregion, "nand-oob-free");
> +}
> +
> +static const struct mtd_ooblayout_ops nand_ooblayout_of_ops = {
> +	.ecc = nand_ooblayout_ecc_of,
> +	.free = nand_ooblayout_free_of,
> +};
> +
>  static int check_offs_len(struct mtd_info *mtd,
>  					loff_t ofs, uint64_t len)
>  {
> @@ -5843,6 +5880,11 @@ static int nand_dt_init(struct nand_chip *chip)
>  	if (of_property_read_bool(dn, "nand-ecc-maximize"))
>  		chip->ecc.options |= NAND_ECC_MAXIMIZE;
>  
> +	if (!chip->mtd.ooblayout &&
> +				of_property_read_bool(dn, "nand-oob-ecc") &&
> +				of_property_read_bool(dn, "nand-oob-free"))
> +		chip->mtd.ooblayout = &nand_ooblayout_of_ops;
> +
>  	return 0;
>  }
>