Re: [PATCH v3 4/4] mtd: mxc_nand: generate nand_ecclayout for 8 bit ECC

Brian Norris
2015-05-20T22:41:20Z

On Wed, May 13, 2015 at 11:17:39AM +0300, Baruch Siach wrote:
> Hardware 8 bit ECC requires a different nand_ecclayout. Instead of adding yet
> another static struct nand_ecclayout, generate it in code.

I like the idea of not adding more static declarations. But I think you
have a potential problem below.

> Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
> Signed-off-by: Baruch Siach <baruch@tkos.co.il>
> ---
> v3:
> Rename ecc_8bit_layout to ecc_8bit_layout_4k (Uwe Kleine-König)
>
> v2:
> Initialize eccbytes
> ---
> drivers/mtd/nand/mxc_nand.c | 22 +++++++++++++++++++++-
> 1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mtd/nand/mxc_nand.c b/drivers/mtd/nand/mxc_nand.c
> index 010be8aa41d4..25759563bf11 100644
> --- a/drivers/mtd/nand/mxc_nand.c
> +++ b/drivers/mtd/nand/mxc_nand.c
> @@ -960,6 +960,23 @@ static int get_eccsize(struct mtd_info *mtd)
> return 8;
> }
>
> +static void ecc_8bit_layout_4k(struct nand_ecclayout *layout)
> +{
> + int i, j;
> +
> + layout->eccbytes = 8*18;
> + for (i = 0; i < 8; i++)
> + for (j = 0; j < 18; j++)
> + layout->eccpos[i*18 + j] = i*26 + j + 7;
> +
> + layout->oobfree[0].offset = 2;
> + layout->oobfree[0].length = 4;
> + for (i = 1; i < 8; i++) {
> + layout->oobfree[i].offset = i*26;
> + layout->oobfree[i].length = 7;
> + }
> +}
> +
> static void preset_v1(struct mtd_info *mtd)
> {
> struct nand_chip *nand_chip = mtd->priv;
> @@ -1636,8 +1653,11 @@ static int mxcnd_probe(struct platform_device *pdev)
>
> if (mtd->writesize == 2048)
> this->ecc.layout = host->devtype_data->ecclayout_2k;
> - else if (mtd->writesize == 4096)
> + else if (mtd->writesize == 4096) {
> this->ecc.layout = host->devtype_data->ecclayout_4k;
> + if (get_eccsize(mtd) == 8)
> + ecc_8bit_layout_4k(this->ecc.layout);

So you're overwriting an existing layout (e.g., nandv2_hw_eccoob_4k).
What if you have more than one NAND chip? You might do better by
dynamically allocating the memory.

> + }
>
> /*
> * Experimentation shows that i.MX NFC can only handle up to 218 oob

Brian