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Subject[PATCH v4 03/23] mtd: nand: add generic helpers to check, match, maximize ECC settings
Date
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@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:
+ 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;
+ 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;
+
+
+ /* 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;
+};
+
+/**
* 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);

--
2.7.4
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