Re: [RFC PATCH v2 6/6] mtd: rawnand: micron: support 8/512 on-die ECC

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

On Tue, 19 Jun 2018 17:31:25 +1200
Chris Packham <chris.packham@alliedtelesis.co.nz> wrote:

> Micron MT29F1G08ABAFAWP-ITE:F supports an on-die ECC with 8 bits
> per 512 bytes. Add support for this combination.
> 
> Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
> ---
> This seems deceptively easy so I've probably missed something. I have
> tested with running some of the ubifs stress tests from mtd-utils and
> things seem OK.
> 
> Changes in v2:
> - New
> 
>  drivers/mtd/nand/raw/nand_micron.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
> index d1e8f57544a0..2164dd112f5c 100644
> --- a/drivers/mtd/nand/raw/nand_micron.c
> +++ b/drivers/mtd/nand/raw/nand_micron.c
> @@ -240,9 +240,9 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
>  
>  	/*
>  	 * Some Micron NANDs have an on-die ECC of 4/512, some other
> -	 * 8/512. We only support the former.
> +	 * 8/512.
>  	 */
> -	if (chip->ecc_strength_ds != 4)
> +	if (chip->ecc_strength_ds != 4 && chip->ecc_strength_ds != 8)
>  		return MICRON_ON_DIE_UNSUPPORTED;

I remember that chips with 8bits/512bytes on-die ECC had an extra
command to query a more precise number of bitflips (see this
discussion [1]). It's probably worth implementing that, since those
chips are more likely to have bitflips than the 4bit/512 versions, and
you don't want to move the data around as soon as you have one bitflip. 

>  
>  	return MICRON_ON_DIE_SUPPORTED;
> @@ -274,9 +274,9 @@ static int micron_nand_init(struct nand_chip *chip)
>  			return -EINVAL;
>  		}
>  
> -		chip->ecc.bytes = 8;
> +		chip->ecc.bytes = chip->ecc_strength_ds * 2;
>  		chip->ecc.size = 512;
> -		chip->ecc.strength = 4;
> +		chip->ecc.strength = chip->ecc_strength_ds;
>  		chip->ecc.algo = NAND_ECC_BCH;
>  		chip->ecc.read_page = micron_nand_read_page_on_die_ecc;
>  		chip->ecc.write_page = micron_nand_write_page_on_die_ecc;

[1]http://lists.infradead.org/pipermail/linux-mtd/2017-March/072974.html