Re: [PATCH v3 01/16] mtd: rawnand: helper function for setting up ECC configuration

[Miquel Raynal]

Hi Abhishek,

On Fri, 25 May 2018 17:51:29 +0530, Abhishek Sahu
<absahu@xxxxxxxxxxxxxx> wrote:

> commit 2c8f8afa7f92 ("mtd: nand: add generic helpers to check,
> match, maximize ECC settings") provides generic helpers which
> drivers can use for setting up ECC parameters.
> 
> Since same board can have different ECC strength nand chips so
> following is the logic for setting up ECC strength and ECC step
> size, which can be used by most of the drivers.
> 
> 1. If both ECC step size and ECC strength are already set
>    (usually by DT) then just check whether this setting
>    is supported by NAND controller.
> 2. If NAND_ECC_MAXIMIZE is set, then select maximum ECC strength
>    supported by NAND controller.
> 3. Otherwise, try to match the ECC step size and ECC strength closest
>    to the chip's requirement. If available OOB size can't fit the chip
>    requirement then select maximum ECC strength which can be fit with
>    available OOB size.
> 
> This patch introduces nand_ecc_choose_conf function which calls the
> required helper functions for the above logic. The drivers can use
> this single function instead of calling the 3 helper functions
> individually.
> 
> CC: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Signed-off-by: Abhishek Sahu <absahu@xxxxxxxxxxxxxx>
> ---
> * Changes from v2:
> 
>   1. Renamed function to nand_ecc_choose_conf.
>   2. Minor code reorganization to remove warning and 2 function calls
>      for nand_maximize_ecc.
> 
> * Changes from v1:
>   NEW PATCH
> 
>  drivers/mtd/nand/raw/nand_base.c | 42 ++++++++++++++++++++++++++++++++++++++++
>  drivers/mtd/nand/raw/nand_base.c | 31 +++++++++++++++++++++++++++++++
>  include/linux/mtd/rawnand.h      |  3 +++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
> index 72f3a89..e52019d 100644
> --- a/drivers/mtd/nand/raw/nand_base.c
> +++ b/drivers/mtd/nand/raw/nand_base.c
> @@ -6249,6 +6249,37 @@ int nand_maximize_ecc(struct nand_chip *chip,
>  }
>  EXPORT_SYMBOL_GPL(nand_maximize_ecc);
>  
> +/**
> + * nand_ecc_choose_conf - Set the ECC strength and ECC step size
> + * @chip: nand chip info structure
> + * @caps: ECC engine caps info structure
> + * @oobavail: OOB size that the ECC engine can use
> + *
> + * Choose the ECC configuration according to following logic
> + *
> + * 1. If both ECC step size and ECC strength are already set (usually by DT)
> + *    then check if it is supported by this controller.
> + * 2. If NAND_ECC_MAXIMIZE is set, then select maximum ECC strength.
> + * 3. Otherwise, try to match the ECC step size and ECC strength closest
> + *    to the chip's requirement. If available OOB size can't fit the chip
> + *    requirement then fallback to the maximum ECC step size and ECC strength.
> + *
> + * On success, the chosen ECC settings are set.
> + */
> +int nand_ecc_choose_conf(struct nand_chip *chip,
> +			 const struct nand_ecc_caps *caps, int oobavail)
> +{
> +	if (chip->ecc.size && chip->ecc.strength)
> +		return nand_check_ecc_caps(chip, caps, oobavail);
> +
> +	if (!(chip->ecc.options & NAND_ECC_MAXIMIZE) &&
> +	    !nand_match_ecc_req(chip, caps, oobavail))
> +		return 0;
> +
> +	return nand_maximize_ecc(chip, caps, oobavail);

I personally don't mind if nand_maximize_ecc() is called twice in
the function if it clarifies the logic. Maybe the following will be
more clear for the user?

	if (chip->ecc.size && chip->ecc.strength)
		return nand_check_ecc_caps(chip, caps, oobavail);

	if (chip->ecc.options & NAND_ECC_MAXIMIZE)
		return nand_maximize_ecc(chip, caps, oobavail);

	if (!nand_match_ecc_req(chip, caps, oobavail))
		return 0;

	return nand_maximize_ecc(chip, caps, oobavail);

Also, I'm not sure we should just error out when nand_check_ecc_caps()
fails. What about something more robust, like:

	int ret;

	if (chip->ecc.size && chip->ecc.strength) {
		ret = nand_check_ecc_caps(chip, caps, oobavail);
		if (ret)
			goto maximize_ecc;

		return 0;
	}

	if (chip->ecc.options & NAND_ECC_MAXIMIZE)
		goto maximize_ecc;

	ret = nand_match_ecc_req(chip, caps, oobavail);
	if (ret)
		goto maximize_ecc;

	return 0;

maximize_ecc:
	return nand_maximize_ecc(chip, caps, oobavail);

> +}
> +EXPORT_SYMBOL_GPL(nand_ecc_choose_conf);
> +
>  /*
>   * Check if the chip configuration meet the datasheet requirements.
>  
> diff --git a/include/linux/mtd/rawnand.h b/include/linux/mtd/rawnand.h
> index 5dad59b..89889fa 100644
> --- a/include/linux/mtd/rawnand.h
> +++ b/include/linux/mtd/rawnand.h
> @@ -1627,6 +1627,9 @@ int nand_match_ecc_req(struct nand_chip *chip,
>  int nand_maximize_ecc(struct nand_chip *chip,
>  		      const struct nand_ecc_caps *caps, int oobavail);
>  
> +int nand_ecc_choose_conf(struct nand_chip *chip,
> +			 const struct nand_ecc_caps *caps, int oobavail);
> +
>  /* Default write_oob implementation */
>  int nand_write_oob_std(struct mtd_info *mtd, struct nand_chip *chip, int page);
>  

Thanks,
MiquÃl