Re: [PATCH v2] mtd: rawnand: micron: handle on-die "ECC-off" devices correctly

[Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>]

On Mon, 29 Jul 2019 09:06:52 +0200
Marco Felsch <m.felsch@xxxxxxxxxxxxxx> wrote:

> Some devices are supposed to do not support on-die ECC but experience

		^ are not supposed to support

> shows that internal ECC machinery can actually be enabled through the
> "SET FEATURE (EFh)" command, even if a read of the "READ ID Parameter
> Tables" returns that it is not.
> 
> Currently, the driver checks the "READ ID Parameter" field directly
> after having enabled the feature. If the check fails it returns
> immediately but leaves the ECC on. When using buggy chips like
> MT29F2G08ABAGA and MT29F2G08ABBGA, all future read/program cycles will
> go through the on-die ECC, confusing the host controller which is
> supposed to be the one handling correction.
> 
> To address this in a common way we need to turn off the on-die ECC
> directly after reading the "READ ID Parameter" and before checking the
> "ECC status".
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: dbc44edbf833 ("mtd: rawnand: micron: Fix on-die ECC detection logic")
> Signed-off-by: Marco Felsch <m.felsch@xxxxxxxxxxxxxx>
> Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> ---
> v2:
> - adapt commit message according Miquel comments
> - add fixes, stable tags
> - add Boris rb-tag
> 
>  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.

								    ^officially.

> +	 * 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;


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