[PATCH v4 03/23] mtd: nand: add generic helpers to check, match, maximize ECC settings
Boris Brezillon
boris.brezillon at free-electrons.com
Tue Jun 6 14:47:33 PDT 2017
On Tue, 6 Jun 2017 08:21:42 +0900
Masahiro Yamada <yamada.masahiro at socionext.com> wrote:
> Driver are responsible for setting up ECC parameters correctly.
> Those include:
> - Check if ECC parameters specified (usually by DT) are valid
> - Meet the chip's ECC requirement
> - Maximize ECC strength if NAND_ECC_MAXIMIZE flag is set
>
> The logic can be generalized by factoring out common code.
>
> This commit adds 3 helpers to the NAND framework:
> nand_check_ecc_caps - Check if preset step_size and strength are valid
> nand_match_ecc_req - Match the chip's requirement
> nand_maximize_ecc - Maximize the ECC strength
>
> To use the helpers above, a driver needs to provide:
> - Data array of supported ECC step size and strength
> - A hook that calculates ECC bytes from the combination of
> step_size and strength.
>
> By using those helpers, code duplication among drivers will be
> reduced.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro at socionext.com>
> ---
>
> Changes since the previous version:
>
> - Step size info holds an array of associated strengths
> - nand_match_ecc_req() does not take care of the case
> where ecc_size/strength is already set
> - Reflect more comments from Boris
>
> Previous version:
> http://patchwork.ozlabs.org/patch/752107/
>
>
> Changes in v4: None
> Changes in v3: None
> Changes in v2: None
>
> drivers/mtd/nand/nand_base.c | 219 +++++++++++++++++++++++++++++++++++++++++++
> include/linux/mtd/nand.h | 35 +++++++
> 2 files changed, 254 insertions(+)
>
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index bdfa903..f2da4f2 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -4509,6 +4509,225 @@ static int nand_set_ecc_soft_ops(struct mtd_info *mtd)
> }
> }
>
> +/**
> + * nand_check_ecc_caps - check the sanity of preset ECC settings
> + * @mtd: mtd info structure
> + * @chip: nand chip info structure
> + * @caps: ECC caps info structure
> + *
> + * When ECC step size and strength are already set, check if they are supported
> + * by the controller and the calculated ECC bytes fit within the chip's OOB.
> + * On success, the calculated ECC bytes is set.
> + */
> +int nand_check_ecc_caps(struct mtd_info *mtd, struct nand_chip *chip,
> + const struct nand_ecc_caps *caps)
> +{
> + const struct nand_ecc_step_info *stepinfo;
> + int avail_oobsize = mtd->oobsize - caps->oob_reserve_bytes;
> + int preset_step = chip->ecc.size;
> + int preset_strength = chip->ecc.strength;
> + int ecc_bytes;
> + int i, j;
> +
> + if (WARN_ON(avail_oobsize < 0))
> + return -EINVAL;
> +
> + if (!preset_step || !preset_strength)
> + return -ENODATA;
> +
> + for (i = 0; i < caps->nstepinfos; i++) {
> + stepinfo = &caps->stepinfos[i];
> +
> + if (stepinfo->stepsize != preset_step)
> + continue;
> +
> + for (j = 0; j < stepinfo->nstrengths; j++) {
> + if (stepinfo->strengths[j] == preset_strength)
> + goto found;
> + }
> + }
> +
> + pr_err("ECC (step, strength) = (%d, %d) not supported on this controller",
> + preset_step, preset_strength);
> +
> + return -ENOTSUPP;
> +
> +found:
I prefer something like:
if (i == caps->nstepinfos) {
pr_err(...);
return -ENOTSUPP;
}
...
instead of this 'found' label.
> + ecc_bytes = caps->calc_ecc_bytes(preset_step, preset_strength);
> + if (WARN_ON_ONCE(ecc_bytes < 0))
> + return ecc_bytes;
> +
> + if (ecc_bytes * mtd->writesize / preset_step > avail_oobsize) {
> + pr_err("ECC (step, strength) = (%d, %d) does not fit in OOB",
> + preset_step, preset_strength);
> + return -ENOSPC;
> + }
> +
> + chip->ecc.bytes = ecc_bytes;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(nand_check_ecc_caps);
> +
> +/**
> + * nand_match_ecc_req - meet the chip's requirement with least ECC bytes
> + * @mtd: mtd info structure
> + * @chip: nand chip info structure
> + * @caps: ECC engine caps info structure
> + *
> + * If a chip's ECC requirement is provided, try to meet it with the least
> + * number of ECC bytes (i.e. with the largest number of OOB-free bytes).
> + * On success, the chosen ECC settings are set.
> + */
> +int nand_match_ecc_req(struct mtd_info *mtd, struct nand_chip *chip,
> + const struct nand_ecc_caps *caps)
> +{
> + const struct nand_ecc_step_info *stepinfo;
> + int avail_oobsize = mtd->oobsize - caps->oob_reserve_bytes;
> + int req_step = chip->ecc_step_ds;
> + int req_strength = chip->ecc_strength_ds;
> + int req_corr, step_size, strength, steps, ecc_bytes, ecc_bytes_total;
> + int best_step, best_strength, best_ecc_bytes;
> + int best_ecc_bytes_total = INT_MAX;
Just nitpicking, but why not -1 instead of INT_MAX?
> + int i, j;
> +
> + if (WARN_ON(avail_oobsize < 0))
> + return -EINVAL;
> +
> + /* No information provided by the NAND chip */
> + if (!req_step || !req_strength)
> + return -ENOTSUPP;
> +
> + /* number of correctable bits the chip requires in a page */
> + req_corr = mtd->writesize / req_step * req_strength;
> +
> + for (i = 0; i < caps->nstepinfos; i++) {
> + stepinfo = &caps->stepinfos[i];
> + step_size = stepinfo->stepsize;
> +
> + for (j = 0; j < stepinfo->nstrengths; j++) {
> + strength = stepinfo->strengths[j];
> +
> + /*
> + * If both step size and strength are smaller than the
> + * chip's requirement, it is not easy to compare the
> + * resulted reliability.
> + */
> + if (step_size < req_step && strength < req_strength)
> + continue;
> +
> + if (mtd->writesize % step_size)
> + continue;
> +
> + steps = mtd->writesize / step_size;
> +
> + ecc_bytes = caps->calc_ecc_bytes(step_size, strength);
> + if (WARN_ON_ONCE(ecc_bytes < 0))
> + continue;
> + ecc_bytes_total = ecc_bytes * steps;
> +
> + if (ecc_bytes_total > avail_oobsize ||
> + strength * steps < req_corr)
> + continue;
> +
> + /*
> + * We assume the best is to meet the chip's requrement
> + * with the least number of ECC bytes.
> + */
> + if (ecc_bytes_total < best_ecc_bytes_total) {
> + best_ecc_bytes_total = ecc_bytes_total;
> + best_step = step_size;
> + best_strength = strength;
> + best_ecc_bytes = ecc_bytes;
> + }
> + }
> + }
> +
> + if (best_ecc_bytes_total == INT_MAX)
> + return -ENOTSUPP;
> +
> + chip->ecc.size = best_step;
> + chip->ecc.strength = best_strength;
> + chip->ecc.bytes = best_ecc_bytes;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(nand_match_ecc_req);
> +
> +/**
> + * nand_maximize_ecc - choose the max ECC strength available
> + * @mtd: mtd info structure
> + * @chip: nand chip info structure
> + * @caps: ECC engine caps info structure
> + *
> + * Choose the max ECC strength that is supported on the controller, and can fit
> + * within the chip's OOB. On success, the chosen ECC settings are set.
> + */
> +int nand_maximize_ecc(struct mtd_info *mtd, struct nand_chip *chip,
> + const struct nand_ecc_caps *caps)
> +{
> + const struct nand_ecc_step_info *stepinfo;
> + int avail_oobsize = mtd->oobsize - caps->oob_reserve_bytes;
> + int step_size, strength, steps, ecc_bytes, corr;
> + int best_corr = 0;
> + int best_step = 0;
> + int best_strength, best_ecc_bytes;
> + int i, j;
> +
> + if (WARN_ON(avail_oobsize < 0))
> + return -EINVAL;
> +
> + for (i = 0; i < caps->nstepinfos; i++) {
> + stepinfo = &caps->stepinfos[i];
> + step_size = stepinfo->stepsize;
> +
> +
Extra blank line here.
> + /* If chip->ecc.size is already set, respect it */
> + if (chip->ecc.size && step_size != chip->ecc.size)
> + continue;
> +
> + for (j = 0; j < stepinfo->nstrengths; j++) {
> + strength = stepinfo->strengths[j];
> +
> + if (mtd->writesize % step_size)
> + continue;
> +
> + steps = mtd->writesize / step_size;
> +
> + ecc_bytes = caps->calc_ecc_bytes(step_size, strength);
> + if (WARN_ON_ONCE(ecc_bytes < 0))
> + continue;
> +
> + if (ecc_bytes * steps > avail_oobsize)
> + continue;
> +
> + corr = strength * steps;
> +
> + /*
> + * If the number of correctable bits is the same,
> + * bigger step_size has more reliability.
> + */
> + if (corr > best_corr ||
> + (corr == best_corr && step_size > best_step)) {
> + best_corr = corr;
> + best_step = step_size;
> + best_strength = strength;
> + best_ecc_bytes = ecc_bytes;
> + }
> + }
> + }
> +
> + if (!best_corr)
> + return -ENOTSUPP;
> +
> + chip->ecc.size = best_step;
> + chip->ecc.strength = best_strength;
> + chip->ecc.bytes = best_ecc_bytes;
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(nand_maximize_ecc);
> +
> /*
> * Check if the chip configuration meet the datasheet requirements.
>
> diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
> index 8f67b15..97ccb76 100644
> --- a/include/linux/mtd/nand.h
> +++ b/include/linux/mtd/nand.h
> @@ -477,6 +477,32 @@ static inline void nand_hw_control_init(struct nand_hw_control *nfc)
> }
>
> /**
> + * struct nand_ecc_step_info - ECC step information of ECC engine
> + * @stepsize: data bytes per ECC step
> + * @strengths: array of supported strengths
> + * @nstrengths: number of supported strengths
> + */
> +struct nand_ecc_step_info {
> + int stepsize;
> + const int *strengths;
> + int nstrengths;
> +};
> +
> +/**
> + * struct nand_ecc_caps - capability of ECC engine
> + * @stepinfos: array of ECC step information
> + * @nstepinfos: number of ECC step information
> + * @calc_ecc_bytes: driver's hook to calculate ECC bytes per step
> + * @oob_reserve_bytes: number of bytes in OOB that must be reserved
> + */
> +struct nand_ecc_caps {
> + const struct nand_ecc_step_info *stepinfos;
> + int nstepinfos;
> + int (*calc_ecc_bytes)(int step_size, int strength);
> + int oob_reserve_bytes;
Why is this needed? I thought we agreed on passing oobavail as an
argument to these helper funcs. If a driver needs to reserve a few OOB
bytes, then doing mtd->oobsize - rsvd_bytes is not such a big deal.
> +};
> +
> +/**
> * struct nand_ecc_ctrl - Control structure for ECC
> * @mode: ECC mode
> * @algo: ECC algorithm
> @@ -1244,6 +1270,15 @@ int nand_check_erased_ecc_chunk(void *data, int datalen,
> void *extraoob, int extraooblen,
> int threshold);
>
> +int nand_check_ecc_caps(struct mtd_info *mtd, struct nand_chip *chip,
> + const struct nand_ecc_caps *caps);
> +
> +int nand_match_ecc_req(struct mtd_info *mtd, struct nand_chip *chip,
> + const struct nand_ecc_caps *caps);
> +
> +int nand_maximize_ecc(struct mtd_info *mtd, struct nand_chip *chip,
> + const struct nand_ecc_caps *caps);
> +
> /* Default write_oob implementation */
> int nand_write_oob_std(struct mtd_info *mtd, struct nand_chip *chip, int page);
>
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