Re: [PATCH] mtd: rawnand: micron: handle "ecc off" devices correctly

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Marco,

+ Richard
+ Working e-mail address for Boris

Marco Felsch <m.felsch@pengutronix.de> wrote on Fri, 26 Jul 2019
09:44:34 +0200:

> Some devices don't support ecc "official". By "official" I mean that the
> feature can be set trough the "SET FEATURE (EFh)" command but isn't
> reported to the "READ ID Parameter Tables". Because the "ECC Field"
> still says that it is disabled. This is applicable at least
> for the MT29F2G08ABAGA and MT29F2G08ABBGA devices. Even worse the
> datasheet describes the ECC feature in chapter "ECC Protection".
> 
> Currently the driver checks the "READ ID Parameter" field directly after
> we enabled the feature. If the check fails we return immediately but
> leave the ECC on. Now all future read/program cycles goes trough the ecc
> and the host nfc gets confused and reports ECC errors.
> 
> To address this in a common way we need to turn off the ECC directly
> after reading the "READ ID Parameter" and before checking the
> "ECC status".
> 
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>

Good catch! However you report that on-die ECC correction is working
but you still disable it; any reason to do so ? Would it be better to
actually enable on-die ECC and explicitly mark these two chips as
buggy (see [1] for checking the chip IDs)?

[1] https://elixir.bootlin.com/linux/v5.3-rc1/source/drivers/mtd/nand/raw/nand_macronix.c#L83

> ---
>  drivers/mtd/nand/raw/nand_micron.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
> index 1622d3145587..fb199ad2f1a6 100644
> --- a/drivers/mtd/nand/raw/nand_micron.c
> +++ b/drivers/mtd/nand/raw/nand_micron.c
> @@ -390,6 +390,14 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
>  	    (chip->id.data[4] & MICRON_ID_INTERNAL_ECC_MASK) != 0x2)
>  		return MICRON_ON_DIE_UNSUPPORTED;
>  
> +	/*
> +	 * It seems that there are devices which do not support ECC official.
> +	 * At least the MT29F2G08ABAGA / MT29F2G08ABBGA devices supports
> +	 * enabling the ECC feature but don't reflect that to the READ_ID table.
> +	 * So we have to guarantee that we disable the ECC feature directly
> +	 * after we did the READ_ID table command. Later we can evaluate the
> +	 * ECC_ENABLE support.
> +	 */
>  	ret = micron_nand_on_die_ecc_setup(chip, true);
>  	if (ret)
>  		return MICRON_ON_DIE_UNSUPPORTED;
> @@ -398,13 +406,13 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
>  	if (ret)
>  		return MICRON_ON_DIE_UNSUPPORTED;
>  
> -	if (!(id[4] & MICRON_ID_ECC_ENABLED))
> -		return MICRON_ON_DIE_UNSUPPORTED;
> -
>  	ret = micron_nand_on_die_ecc_setup(chip, false);
>  	if (ret)
>  		return MICRON_ON_DIE_UNSUPPORTED;
>  
> +	if (!(id[4] & MICRON_ID_ECC_ENABLED))
> +		return MICRON_ON_DIE_UNSUPPORTED;
> +
>  	ret = nand_readid_op(chip, 0, id, sizeof(id));
>  	if (ret)
>  		return MICRON_ON_DIE_UNSUPPORTED;

Thanks,
Miquèl

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