Re: [PATCH] mtd: rawnand: fsmc: Fix Hamming ECC

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Tue,  4 Sep 2018 11:14:38 +0200
Boris Brezillon <boris.brezillon@bootlin.com> wrote:

> Apparently ECC bytes are not ordered as expected by nand_correct_data()
> in the ecc_calc buffer which leads to invalid bitflip correction when
> an ECC error is detected (can be reproduced with 'nandbiterrs -i').
> 
> Re-ordering ECC bytes seems to fix the problem.
> 
> While at it, get rid of the useless u8 cast.
> 
> Fixes: 6c009ab89a21 ("mtd: generic FSMC NAND MTD driver")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> ---
>  drivers/mtd/nand/raw/fsmc_nand.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/nand/raw/fsmc_nand.c b/drivers/mtd/nand/raw/fsmc_nand.c
> index f418236fa020..c79f8e965b38 100644
> --- a/drivers/mtd/nand/raw/fsmc_nand.c
> +++ b/drivers/mtd/nand/raw/fsmc_nand.c
> @@ -440,9 +440,9 @@ static int fsmc_read_hwecc_ecc1(struct mtd_info *mtd, const uint8_t *data,
>  	uint32_t ecc_tmp;
>  
>  	ecc_tmp = readl_relaxed(host->regs_va + ECC1);
> -	ecc[0] = (uint8_t) (ecc_tmp >> 0);
> -	ecc[1] = (uint8_t) (ecc_tmp >> 8);
> -	ecc[2] = (uint8_t) (ecc_tmp >> 16);
> +	ecc[0] = ecc_tmp >> 8;
> +	ecc[1] = ecc_tmp;
> +	ecc[2] = ecc_tmp >> 16;

Hm, looks like there's a Kconfig option (CONFIG_MTD_NAND_ECC_SMC) to let
nand_ecc_correct() swap those 2 bytes for us, but it's clearly not a
good thing to take this decision based on a Kconfig option (does not
work if you want the same kernel to be used on various platforms).

I'll come up with a better solution.