[PATCH 1/2] mtd: nand: add generic helpers to check, match, maximize ECC settings
Masahiro Yamada
yamada.masahiro at socionext.com
Wed Apr 19 00:06:57 PDT 2017
Each driver has been responsible for:
- Check if ECC setting specified (mostly by DT) is valid
- Meet the chip's required ECC strength
- Maximize the strength when NAND_ECC_MAXIMIZE flag is set
The logic can be generalized by factoring out driver-specific
parameters. A driver provides:
- Array of (step_size, strength) supported on the controller
- A hook that calculates ECC bytes from the combination of
(step_size, strength).
Then, this commit provides 3 helper functions:
nand_check_ecc_caps - Check if preset (step_size, strength) is valid
nand_try_to_match_ecc_req - Match the chip's requirement
nand_try_to_maximize_ecc - Maximize the ECC strength
These helpers will save duplicated code among drivers.
Signed-off-by: Masahiro Yamada <yamada.masahiro at socionext.com>
---
drivers/mtd/nand/nand_base.c | 178 +++++++++++++++++++++++++++++++++++++++++++
include/linux/mtd/nand.h | 31 ++++++++
2 files changed, 209 insertions(+)
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 0670e13..ee43e5e 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -4539,6 +4539,184 @@ static int nand_set_ecc_soft_ops(struct mtd_info *mtd)
}
}
+/**
+ * nand_check_ecc_caps - check if ECC step size and strength is supported
+ * @mtd: mtd info structure
+ * @chip: nand chip info structure
+ * @caps: ECC engine caps info structure
+ *
+ * When ECC step size and strength are set, check if the combination is really
+ * supported by the controller and fit within the chip's OOB. On success,
+ * ECC bytes per step is set.
+ */
+int nand_check_ecc_caps(struct mtd_info *mtd, struct nand_chip *chip,
+ const struct nand_ecc_engine_caps *caps)
+{
+ const struct nand_ecc_setting *setting;
+ int preset_step = chip->ecc.size;
+ int preset_strength = chip->ecc.strength;
+ int ecc_bytes;
+
+ if (!preset_step || !preset_strength)
+ return -ENODATA;
+
+ for (setting = caps->ecc_settings; setting->step; setting++) {
+ if (setting->step != preset_step ||
+ setting->strength != preset_strength)
+ continue;
+
+ ecc_bytes = caps->calc_ecc_bytes(setting);
+ if (WARN_ON_ONCE(ecc_bytes < 0))
+ continue;
+
+ if (ecc_bytes * mtd->writesize / setting->step >
+ caps->avail_oobsize) {
+ pr_err("ECC (step, strength) = (%d, %d) does not fit in OOB",
+ setting->step, setting->strength);
+ return -ENOSPC;
+ }
+
+ chip->ecc.bytes = ecc_bytes;
+ return 0;
+ }
+
+ pr_err("ECC (step, strength) = (%d, %d) not supported on this controller",
+ preset_step, preset_strength);
+
+ return -ENOTSUPP;
+}
+
+/**
+ * nand_try_to_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 chip's ECC requirement is available, try to meet it with the least number
+ * number of ECC bytes (i.e. with the largest number of OOB-free bytes).
+ * On success, the chosen ECC settings are set.
+ */
+int nand_try_to_match_ecc_req(struct mtd_info *mtd, struct nand_chip *chip,
+ const struct nand_ecc_engine_caps *caps)
+{
+ const struct nand_ecc_setting *setting, *best_setting = NULL;
+ int req_step = chip->ecc_step_ds;
+ int req_strength = chip->ecc_strength_ds;
+ int req_corr, steps, ecc_bytes, ecc_bytes_total;
+ int best_ecc_bytes, best_ecc_bytes_total = INT_MAX;
+
+ /* 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 (setting = caps->ecc_settings; setting->step; setting++) {
+ /* If chip->ecc.size is already set, respect it. */
+ if (chip->ecc.size && setting->step != chip->ecc.size)
+ continue;
+
+ /* If chip->ecc.strength is already set, respect it. */
+ if (chip->ecc.strength &&
+ setting->strength != chip->ecc.strength)
+ continue;
+
+ /*
+ * If the controller's step size is smaller than the chip's
+ * requirement, comparison of the strength is not simple.
+ */
+ if (setting->step < req_step)
+ continue;
+
+ steps = mtd->writesize / setting->step;
+
+ ecc_bytes = caps->calc_ecc_bytes(setting);
+ if (WARN_ON_ONCE(ecc_bytes < 0))
+ continue;
+ ecc_bytes_total = ecc_bytes * steps;
+
+ if (ecc_bytes_total > caps->avail_oobsize ||
+ setting->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_setting = setting;
+ best_ecc_bytes = ecc_bytes;
+ }
+ }
+
+ if (!best_setting)
+ return -ENOTSUPP;
+
+ chip->ecc.size = best_setting->step;
+ chip->ecc.strength = best_setting->strength;
+ chip->ecc.bytes = best_ecc_bytes;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(nand_try_to_match_ecc_req);
+
+/**
+ * nand_try_to_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_try_to_maximize_ecc(struct mtd_info *mtd, struct nand_chip *chip,
+ const struct nand_ecc_engine_caps *caps)
+{
+ const struct nand_ecc_setting *setting, *best_setting = NULL;
+ int steps, ecc_bytes, corr;
+ int best_corr = 0;
+ int best_ecc_bytes;
+
+ for (setting = caps->ecc_settings; setting->step; setting++) {
+ /* If chip->ecc.size is already set, respect it. */
+ if (chip->ecc.size && setting->step != chip->ecc.size)
+ continue;
+
+ steps = mtd->writesize / setting->step;
+ ecc_bytes = caps->calc_ecc_bytes(setting);
+ if (WARN_ON_ONCE(ecc_bytes < 0))
+ continue;
+
+ if (ecc_bytes * steps > caps->avail_oobsize)
+ continue;
+
+ corr = setting->strength * steps;
+
+ /*
+ * If the number of correctable bits is the same,
+ * bigger ecc_step has more reliability.
+ */
+ if (corr > best_corr ||
+ (corr == best_corr && setting->step > best_setting->step)) {
+ best_corr = corr;
+ best_setting = setting;
+ best_ecc_bytes = ecc_bytes;
+ }
+ }
+
+ if (!best_setting)
+ return -ENOTSUPP;
+
+ chip->ecc.size = best_setting->step;
+ chip->ecc.strength = best_setting->strength;
+ chip->ecc.bytes = best_ecc_bytes;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(nand_try_to_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 2ae781e..394128f 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -486,6 +486,28 @@ static inline void nand_hw_control_init(struct nand_hw_control *nfc)
}
/**
+ * struct nand_ecc_setting - information of ECC step supported by ECC engine
+ * @step: data bytes per ECC step
+ * @bytes: ECC bytes per step
+ */
+struct nand_ecc_setting {
+ int step;
+ int strength;
+};
+
+/**
+ * struct nand_ecc_engine_caps - capability of ECC engine
+ * @ecc_settings: array of (step, strength) supported by this ECC engine
+ * @calc_ecc_bytes: driver's hook to calculate ECC bytes per step
+ * @avail_oobsize: OOB size that the ECC engine can use for ECC correction
+ */
+struct nand_ecc_engine_caps {
+ const struct nand_ecc_setting *ecc_settings;
+ int (*calc_ecc_bytes)(const struct nand_ecc_setting *ecc_setting);
+ int avail_oobsize;
+};
+
+/**
* struct nand_ecc_ctrl - Control structure for ECC
* @mode: ECC mode
* @algo: ECC algorithm
@@ -1208,6 +1230,15 @@ 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_engine_caps *caps);
+
+int nand_try_to_match_ecc_req(struct mtd_info *mtd, struct nand_chip *chip,
+ const struct nand_ecc_engine_caps *caps);
+
+int nand_try_to_maximize_ecc(struct mtd_info *mtd, struct nand_chip *chip,
+ const struct nand_ecc_engine_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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