[U-Boot,1/4,v3] mtd: nand: fsmc: Add BCH4 SW ECC support for SPEAr600

This patch adds support for 4-bit ECC BCH4 for the SPEAr600 SoC. This can
be used by boards equipped with a NAND chip that requires 4-bit ECC strength.
The SPEAr600 HW ECC only supports 1-bit ECC strength.

To enable SW BCH4, you need to specify this in your config header:

And use the command "nandecc bch4" to select this ECC scheme upon runtime.

Tested on SPEAr600 x600 board.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Scott Wood <scottwood@freescale.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
---
v3:
- Don't set .caclulate, .correct, and .bytes for NAND_ECC_SOFT_BCH as this
  will be done in nand_scan_tail()
- Set .caclulate back to fsmc_read_hwecc() in the HW case
- Added comment that this function will only be called on SPEAr platforms,
  not supporting the BCH8 HW ECC (FSMC_VER8)

v2:
- Removed err = 0 initialization as suggested by Viresh
- Completed the commit text
- Added Viresh's Acked-by

 drivers/mtd/nand/fsmc_nand.c | 47 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

On Fri, 2015-09-11 at 08:23 +0200, Stefan Roese wrote:
> This patch adds support for 4-bit ECC BCH4 for the SPEAr600 SoC. This can
> be used by boards equipped with a NAND chip that requires 4-bit ECC 
> strength.
> The SPEAr600 HW ECC only supports 1-bit ECC strength.
> 
> To enable SW BCH4, you need to specify this in your config header:
> 
> And use the command "nandecc bch4" to select this ECC scheme upon runtime.
> 
> Tested on SPEAr600 x600 board.
> 
> Signed-off-by: Stefan Roese <sr@denx.de>
> Cc: Scott Wood <scottwood@freescale.com>
> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
> ---
> v3:
> - Don't set .caclulate, .correct, and .bytes for NAND_ECC_SOFT_BCH as this
>   will be done in nand_scan_tail()
> - Set .caclulate back to fsmc_read_hwecc() in the HW case
> - Added comment that this function will only be called on SPEAr platforms,
>   not supporting the BCH8 HW ECC (FSMC_VER8)
> 
> v2:
> - Removed err = 0 initialization as suggested by Viresh
> - Completed the commit text
> - Added Viresh's Acked-by
> 
>  drivers/mtd/nand/fsmc_nand.c | 47 
> ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/drivers/mtd/nand/fsmc_nand.c b/drivers/mtd/nand/fsmc_nand.c
> index 567eff0..fe57b16 100644
> --- a/drivers/mtd/nand/fsmc_nand.c
> +++ b/drivers/mtd/nand/fsmc_nand.c
> @@ -390,6 +390,53 @@ static int fsmc_read_page_hwecc(struct mtd_info *mtd, 
> struct nand_chip *chip,
>       return 0;
>  }
>  
> +#ifndef CONFIG_SPL_BUILD
> +/*
> + * fsmc_nand_switch_ecc - switch the ECC operation between different 
> engines
> + *
> + * @eccstrength              - the number of bits that could be corrected
> + *                     (1 - HW, 4 - SW BCH4)
> + */
> +int __maybe_unused fsmc_nand_switch_ecc(uint32_t eccstrength)

Why do you need __maybe_unused on a non-static function?

> +{
> +     struct nand_chip *nand;
> +     struct mtd_info *mtd;
> +     int err;
> +
> +     /*
> +      * This functions is only called on SPEAr600 platforms, supporting
> +      * 1 bit HW ECC. The BCH8 HW ECC (FSMC_VER8) from the ST-Ericsson
> +      * Nomadik SoC is currently supporting this fsmc_nand_switch_ecc()
> +      * function, as it doesn't need to switch to a different ECC layout.
> +      */
> +     mtd = &nand_info[nand_curr_device];
> +     nand = mtd->priv;
> +
> +     /* Setup the ecc configurations again */
> +     if (eccstrength == 1) {
> +             nand->ecc.mode = NAND_ECC_HW;
> +             nand->ecc.bytes = 3;
> +             nand->ecc.strength = 1;
> +             nand->ecc.layout = &fsmc_ecc1_layout;
> +             nand->ecc.calculate = fsmc_read_hwecc;
> +             nand->ecc.correct = nand_correct_data;
> +     } else {
> +             /*
> +              * .calculate .correct and .bytes will be set in
> +              * nand_scan_tail()
> +              */
> +             nand->ecc.mode = NAND_ECC_SOFT_BCH;
> +             nand->ecc.strength = 4;
> +             nand->ecc.layout = NULL;
> +     }

Even though you say this function will currently not be called on systems 
with BCH8 hardware, it would be good to at least test explicitly for 
eccstrength == 4 and error out if something other than 1 or 4 is requested.

-Scott