Re: [PATCH] fsl_ifc_nand: Added dts support for SW BCH ECC

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

On Tue,  6 Sep 2016 14:32:37 -0500
Matt Weber <matthew.weber@rockwellcollins.com> wrote:

> Added "nand-sw-ecc-bch", "nand-sw-ecc-block" and "nand-sw-ecc-strength"
> properties for software based BCH ECC. So if driver finds these
> properies in DTS NAND flash node, it disables HW ECC and sets ecc
> mode to NAND_ECC_SOFT_BCH and initializes ecc params.

Please don't do that. We already have standard properties to select the
ECC engine and its config (nand-ecc-mode, nand-ecc-algo,
nand-ecc-strength and nand-ecc-step-size).

You even don't have to manually parse these properties, all you have to
do is test the chip->ecc.mode and chip->ecc.algo after you've called
nand_scan_ident(). Based on these values, you can decide to
configure/use your ECC engine or let the core initialize the SW ECC
engine for you.

> 
> Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
> Signed-off-by: sgtandel <sanjay.tandel@rockwellcollins.com>
> ---
>  drivers/mtd/nand/fsl_ifc_nand.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/fsl_ifc_nand.c b/drivers/mtd/nand/fsl_ifc_nand.c
> index 4e9e5fd..1d74ce5 100644
> --- a/drivers/mtd/nand/fsl_ifc_nand.c
> +++ b/drivers/mtd/nand/fsl_ifc_nand.c
> @@ -806,7 +806,8 @@ static int fsl_ifc_chip_init(struct fsl_ifc_mtd *priv)
>  	struct fsl_ifc_runtime __iomem *ifc_runtime = ctrl->rregs;
>  	struct nand_chip *chip = &priv->chip;
>  	struct mtd_info *mtd = nand_to_mtd(&priv->chip);
> -	u32 csor;
> +	u32 csor, csor_swecc;
> +	struct device_node *np = priv->dev->of_node;
>  
>  	/* Fill in fsl_ifc_mtd structure */
>  	mtd->dev.parent = priv->dev;
> @@ -879,8 +880,35 @@ static int fsl_ifc_chip_init(struct fsl_ifc_mtd *priv)
>  		return -ENODEV;
>  	}
>  
> +	/* Independent of u-boot's csor settings, If we have "nand-sw-ecc-bch40"
> +	   property set in device tree's nand flash node, enable 40-bit sw bch ecc */
> +	if (of_property_read_bool(np, "nand-sw-ecc-bch")) {
> +
> +		csor_swecc = csor & (~CSOR_NAND_ECC_DEC_EN &
> +				~CSOR_NAND_ECC_ENC_EN & ~CSOR_NAND_ECC_MODE_8);
> +		ifc_out32(csor_swecc, &ifc_global->csor_cs[priv->bank].csor);
> +		chip->ecc.mode = NAND_ECC_SOFT_BCH;
> +
> +		/* ECC Block */
> +		if (of_property_read_u32(np, "nand-sw-ecc-block", &chip->ecc.size)) {
> +			dev_warn(priv->dev,"devicetree nand-sw-ecc-block property not found\n");
> +			chip->ecc.size = 1024;		/* ECC block default */
> +		}
> +
> +		/* ECC Strength */
> +		if (of_property_read_u32(np, "nand-sw-ecc-strength", &chip->ecc.strength)) {
> +			dev_warn(priv->dev,"devicetree nand-sw-ecc-strength property not found\n");
> +			chip->ecc.strength = 40;	/* 40-bit ECC */
> +		}
> +
> +		 /* Enough bytes to store m*t bits */
> +		chip->ecc.bytes = ((fls(1 + 8 * chip->ecc.size) * chip->ecc.strength) + 7) / 8;
> +		chip->ecc.layout = NULL;
> +		dev_dbg(priv->dev, "NAND_ECC_SOFT_BCH enabled. Strength %d per %d bytes. m*t=%d\n",
> +						chip->ecc.strength, chip->ecc.size, chip->ecc.bytes);
> +	}
>  	/* Must also set CSOR_NAND_ECC_ENC_EN if DEC_EN set */
> -	if (csor & CSOR_NAND_ECC_DEC_EN) {
> +	else if (csor & CSOR_NAND_ECC_DEC_EN) {
>  		chip->ecc.mode = NAND_ECC_HW;
>  		mtd_set_ooblayout(mtd, &fsl_ifc_ooblayout_ops);
>