Re: [PATCH v2 3/3] Add 4-bit ECC support for large page NAND chips on Davinci

[Troy Kisky <troy.kisky@boundarydevices.com>]

s-paulraj@ti.com wrote:
> From: Sandeep Paulraj <s-paulraj@ti.com>
> 
> The patch applies to linux-mtd GIT tree
> 
> This patch adds 4-bit ECC support for large page NAND chips using the new ECC
> mode NAND_ECC_HW_OOB_FIRST. The platform data from board-dm355-evm has been
> adjusted to use this mode.
> 
> The patches have been verified on DM355 device with 2K and 4K page size 
> Micron devices using mtd-tests.
> Error correction upto 4-bits has also been verified using
> nandwrite/nanddump utilities.
> 
> Reviewed-by: David Brownell <dbrownell@users.sourceforge.net>
> Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
> Signed-off-by: Sneha Narnakaje <nsnehaprabha@ti.com>
> ---
>  drivers/mtd/nand/davinci_nand.c |   65 ++++++++++++++++++++++++++++++++++----
>  1 files changed, 58 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
> index ba6940d..2ff0712 100644
> --- a/drivers/mtd/nand/davinci_nand.c
> +++ b/drivers/mtd/nand/davinci_nand.c
> @@ -500,6 +500,49 @@ static struct nand_ecclayout hwecc4_small __initconst = {
>  	},
>  };
>  
> +/* An ECC layout for using 4-bit ECC with large-page (2048bytes) flash,
> + * storing ten ECC bytes plus the manufacturer's bad block marker byte,
> + * and not overlapping the default BBT markers.
> + */
> +static struct nand_ecclayout hwecc4_2048 __initconst = {
> +	.eccbytes = 40,
> +	.eccpos = { /* 2 bytes at offset 0 hold the badblock markers */
> +		/* 4 bytes at offset 8 hold BBT header */
> +		/* 1 byte at offset 12 holds BBT version */
> +		/* 8 bytes at offset 16 hold JFFS2 clean markers */
> +		24, 25, 26, 27, 28, 29,	30, 31, 32, 33,
> +		34, 35, 36, 37, 38, 39,	40, 41, 42, 43,
> +		44, 45, 46, 47, 48, 49, 50, 51, 52, 53,
> +		54, 55, 56, 57, 58, 59, 60, 61, 62, 63, },
> +	.oobfree = {
> +		{.offset = 16, .length = 8, },

why not  offset = 2, length = 22
Won't the badblock marker show if this is used as a BBT?
Can JFFS2 not use the same bytes when not a BBT?

> +		{.offset = 64, },

You can kill the above line.

> +	},
> +};
> +
> +/* An ECC layout for using 4-bit ECC with large-page (4096bytes) flash,
> + * storing ten ECC bytes plus the manufacturer's bad block marker byte,
> + * and not overlapping the default BBT markers.
> + */
> +static struct nand_ecclayout hwecc4_4096 __initconst = {
> +	.eccbytes = 80,
> +	.eccpos = { /* 2 bytes at offset 0 hold the badblock markers */
> +		/* 4 bytes at offset 8 hold BBT header */
> +		/* 1 byte at offset 12 holds BBT version */
> +		/* 8 bytes at offset 16 hold JFFS2 clean markers */
> +		24, 25, 26, 27, 28, 29,	30, 31, 32, 33,
> +		34, 35, 36, 37, 38, 39,	40, 41, 42, 43,
> +		44, 45, 46, 47, 48, 49, 50, 51, 52, 53,
> +		54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
> +		64, 65, 66, 67, 68, 69, 70, 71, 72, 73,
> +		74, 75, 76, 77, 78, 69,	80, 81, 82, 83,
> +		84, 85, 86, 87, 88, 89, 90, 91, 92, 93,
> +		94, 95, 96, 97, 98, 99, 100, 101, 102, 103, },

Can these not be at the end??? i.e. 48-127

> +	.oobfree = {
> +		{.offset = 16, .length = 8, },
> +		{.offset = 104, },
> +	},
> +};
>  
>  static int __init nand_davinci_probe(struct platform_device *pdev)
>  {
> @@ -689,15 +732,23 @@ static int __init nand_davinci_probe(struct platform_device *pdev)
>  				info->mtd.oobsize - 16;
>  			goto syndrome_done;
>  		}
> +		if (chunks == 4) {
> +			info->ecclayout = hwecc4_2048;
> +			info->ecclayout.oobfree[1].length = info->mtd.oobsize -
> +				info->ecclayout.oobfree[1].offset;

This can be removed, it is already 0.

> +			info->chip.ecc.mode = NAND_ECC_HW_OOB_FIRST;
> +			goto syndrome_done;
> +		}
> +		if (chunks == 8) {
> +			info->ecclayout = hwecc4_4096;
> +			info->ecclayout.oobfree[1].length = info->mtd.oobsize -
> +				info->ecclayout.oobfree[1].offset;
> +			info->chip.ecc.mode = NAND_ECC_HW_OOB_FIRST;
> +			goto syndrome_done;
> +		}
>  
> -		/* For large page chips we'll be wanting to use a
> -		 * not-yet-implemented mode that reads OOB data
> -		 * before reading the body of the page, to avoid
> -		 * the "infix OOB" model of NAND_ECC_HW_SYNDROME
> -		 * (and preserve manufacturer badblock markings).
> -		 */
>  		dev_warn(&pdev->dev, "no 4-bit ECC support yet "
> -				"for large page NAND\n");
> +				"for >4K page NAND\n");
>  		ret = -EIO;
>  		goto err_scan;
>