Re: [PATCH] mtd: nand: samsung: Disable subpage writes on E-die NAND

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Tue, 9 Jan 2018 00:48:37 +0100
Ladislav Michl <ladis@linux-mips.org> wrote:

> Samsung E-die SLC NAND manufactured using 21nm process supports only

I would add the chip name here (K9F1G08U0E).

> 1 partial program cycle, so disable subpage writes for it.

Which means it does not support partial page programming, so how about
rewording it like that:

Samsung E-die SLC NAND manufactured using 21nm process (K9F1G08U0E)
does not support partial page programming, so disable subpage writes
for it.

> Manufacturing process is stored in lowest two bits of 5th ID byte.
> 
> Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
> ---
>  Note: Patch generated and tested against next-20180108 on at91sam9g20
>        board with K9F1G08U0E.

Just out of curiosity, what are the symptoms when you don't have this
flag set?

> 
>  drivers/mtd/nand/nand_samsung.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/nand/nand_samsung.c b/drivers/mtd/nand/nand_samsung.c
> index f6b0a63a068c..9400b4a84243 100644
> --- a/drivers/mtd/nand/nand_samsung.c
> +++ b/drivers/mtd/nand/nand_samsung.c
> @@ -92,10 +92,17 @@ static void samsung_nand_decode_id(struct nand_chip *chip)
>  	} else {
>  		nand_decode_ext_id(chip);
>  
> -		/* Datasheet values for SLC Samsung K9F4G08U0D-S[I|C]B0(T00) */
> -		if (nand_is_slc(chip) && chip->id.data[1] == 0xDC) {
> -			chip->ecc_step_ds = 512;
> -			chip->ecc_strength_ds = 1;
> +		if (nand_is_slc(chip)) {
> +			/* K9F4G08U0D-S[I|C]B0(T00) */
> +			if (chip->id.data[1] == 0xDC) {
> +				chip->ecc_step_ds = 512;
> +				chip->ecc_strength_ds = 1;
> +			}
> +
> +			/* 21nm chips do not support partial page write */
> +			if (chip->id.len > 4 &&
> +			    (chip->id.data[4] & GENMASK(1,0)) == 0x1)

NAND vendors tend to change their ID decoding scheme a lot, so maybe we
should be more restrictive here: replace "chip->id.len > 4" by
"chip->id.len == 5" and restrict it to chip->id.data[1] == 0xF1.

> +				chip->options |= NAND_NO_SUBPAGE_WRITE;
>  		}
>  	}
>  }