Subject: Re: [RFC PATCH 25/27] mtd: nand: Add helpers to manage ECC engines and configurations

From: Boris Brezillon <[email-masked]>
Date: Fri, 22 Feb 2019 15:44:31 +0100

On Thu, 21 Feb 2019 13:58:04 +0100
Miquel Raynal <[email-masked]> wrote:

> Add the logic in the NAND core to find the right ECC engine depending
> on the NAND chip requirements and the user desires. Right now, the
> choice may be made between (more will come):
> * software Hamming
> * software BCH
> * on-die (SPI-NAND devices only)
> 
> Once the ECC engine has been found, the ECC engine must be
> configured.
> 
> Signed-off-by: Miquel Raynal <[email-masked]>
> ---
>  drivers/mtd/nand/core.c  | 107 +++++++++++++++++++++++++++++++++++++++
>  include/linux/mtd/nand.h |   4 ++
>  2 files changed, 111 insertions(+)
> 
> diff --git a/drivers/mtd/nand/core.c b/drivers/mtd/nand/core.c
> index 872d46b5fc0f..9feb118c9f68 100644
> --- a/drivers/mtd/nand/core.c
> +++ b/drivers/mtd/nand/core.c
> @@ -207,6 +207,113 @@ int nanddev_mtd_max_bad_blocks(struct mtd_info *mtd, loff_t offs, size_t len)
>  }
>  EXPORT_SYMBOL_GPL(nanddev_mtd_max_bad_blocks);
>  
> +/**
> + * nanddev_find_ecc_engine() - Find a suitable ECC engine
> + * @nand: NAND device
> + */
> +static int nanddev_find_ecc_engine(struct nand_device *nand)

Can we pass the conf in argument instead of reading it from
nand->ecc.user_conf?

> +{
> +	bool is_spinand = mtd_type_is_spinand(&nand->mtd);

And here is the reason for the SPINAND type.

> +
> +	/* Read the user desires in terms of ECC engine/configuration */
> +	nand_ecc_read_user_conf(nand);
> +
> +	/* No ECC engine requestedn, let's return without error */
> +	if (nand->ecc.user_conf.mode == NAND_ECC_NONE)
> +		return 0;
> +
> +	/* Raw NAND default mode is hardware */
> +	if (!is_spinand && nand->ecc.user_conf.mode < 0)
> +		nand->ecc.user_conf.mode = NAND_ECC_HW;

We should let the raw NAND layer take this decision (actually, it's
even a raw NAND controller driver decision). Please complain if
user_conf.mode is invalid.
This way you won't need the SPINAND type you added in one of your
previous patch.

> +
> +	/* SPI-NAND default mode is on-die */
> +	if (is_spinand && nand->ecc.user_conf.mode < 0)
> +		nand->ecc.user_conf.mode = NAND_ECC_ON_DIE;
> +
> +	switch (nand->ecc.user_conf.mode) {
> +	case NAND_ECC_SOFT:
> +		nand->ecc.engine = nand_ecc_sw_get_engine(nand);
> +		break;
> +	case NAND_ECC_ON_DIE:
> +		if (is_spinand)
> +			nand->ecc.engine = spinand_ondie_ecc_get_engine();

So, maybe it's worth having the ondie ECC engine instance directly
embedded in nand_device instead of spinand, or maybe just a pointer, so
that you don't reserve extra space when the NAND device does not have
on-die ECC.

> +		else
> +			pr_err("On-die ECC engines for non SPI devices not supported yet\n");
> +		break;
> +	case NAND_ECC_HW:
> +		pr_err("Hardware ECC engines not supported yet\n");
> +		break;
> +	default:
> +		pr_err("Missing ECC engine property\n");
> +	}
> +
> +	if (!nand->ecc.engine)
> +		return  -EINVAL;
> +
> +	return 0;
> +}

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