linux-kernel - Re: [PATCH -next v3 1/2] mtd: nand: toshiba: Retrieve ECC requirements from extended ID

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Message-ID: <20171206160805.2435094b@bbrezillon>
Date:   Wed, 6 Dec 2017 16:08:05 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     KOBAYASHI Yoshitake <yoshitake.kobayashi@...hiba.co.jp>
Cc:     richard@....at, dwmw2@...radead.org, computersforpeace@...il.com,
        marek.vasut@...il.com, cyrille.pitchen@...ev4u.fr,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v3 1/2] mtd: nand: toshiba: Retrieve ECC
 requirements from extended ID

On Wed,  6 Dec 2017 23:04:57 +0900
KOBAYASHI Yoshitake <yoshitake.kobayashi@...hiba.co.jp> wrote:

> This patch enables support to read the ECC strength and size from the
> NAND flash using Toshiba Memory SLC NAND extended-ID. This patch is
> based on the information of the 6th ID byte of the Toshiba Memory SLC
> NAND.
> 
> Signed-off-by: KOBAYASHI Yoshitake <yoshitake.kobayashi@...hiba.co.jp>
> ---
>  drivers/mtd/nand/nand_toshiba.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/mtd/nand/nand_toshiba.c b/drivers/mtd/nand/nand_toshiba.c
> index 57df857..c2c141b 100644
> --- a/drivers/mtd/nand/nand_toshiba.c
> +++ b/drivers/mtd/nand/nand_toshiba.c
> @@ -35,6 +35,34 @@ static void toshiba_nand_decode_id(struct nand_chip *chip)
>  	    (chip->id.data[5] & 0x7) == 0x6 /* 24nm */ &&
>  	    !(chip->id.data[4] & 0x80) /* !BENAND */)
>  		mtd->oobsize = 32 * mtd->writesize >> 9;
> +
> +	/*
> +	 * Extract ECC requirements from 6th id byte.
> +	 * For Toshiba SLC, ecc requrements are as follows:
> +	 *  - 43nm: 1 bit ECC for each 512Byte is required.
> +	 *  - 32nm: 4 bit ECC for each 512Byte is required.
> +	 *  - 24nm: 8 bit ECC for each 512Byte is required.
> +	 */
> +	if (chip->id.len >= 6 && nand_is_slc(chip)) {
> +		chip->ecc_step_ds = 512;
> +		switch (chip->id.data[5] & 0x7) {
> +		case 0x4:
> +			chip->ecc_strength_ds = 1;
> +			break;
> +		case 0x5:
> +			chip->ecc_strength_ds = 4;
> +			break;
> +		case 0x6:
> +			chip->ecc_strength_ds = 8;
> +			break;
> +		default:
> +			WARN(1, "Could not get ECC info");
> +			chip->ecc_step_ds = 0;
> +			break;
> +		}
> +	} else if (chip->id.len < 6 && nand_is_slc(chip)) {
> +		WARN(1, "Could not get ECC info, 6th nand id byte does not exist.");

I'm pretty sure you have old NAND chips that do not have 6bytes ids
(see the table here [1]), and printing a huge backtrace in this case is
probably not what you want.

If you're okay with dropping this else block, I'll do the change when
applying, no need to send a new version.

> +	}
>  }
>  
>  static int toshiba_nand_init(struct nand_chip *chip)