Introduction of the MTD pairing scheme concept.

2024-11-10 14:11:52 +00:00 · 2016-10-08 12:23:37 -07:00 · 2016-10-08 12:23:37 -07:00 · 69db4aa44f
commit 69db4aa44f
parent f5b88de284 477b0229ac
3 changed files with 212 additions and 0 deletions
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@ -375,6 +375,110 @@ static int mtd_reboot_notifier(struct notifier_block *n, unsigned long state,
 	return NOTIFY_DONE;
 }

+/**
+ * mtd_wunit_to_pairing_info - get pairing information of a wunit
+ * @mtd: pointer to new MTD device info structure
+ * @wunit: write unit we are interested in
+ * @info: returned pairing information
+ *
+ * Retrieve pairing information associated to the wunit.
+ * This is mainly useful when dealing with MLC/TLC NANDs where pages can be
+ * paired together, and where programming a page may influence the page it is
+ * paired with.
+ * The notion of page is replaced by the term wunit (write-unit) to stay
+ * consistent with the ->writesize field.
+ *
+ * The @wunit argument can be extracted from an absolute offset using
+ * mtd_offset_to_wunit(). @info is filled with the pairing information attached
+ * to @wunit.
+ *
+ * From the pairing info the MTD user can find all the wunits paired with
+ * @wunit using the following loop:
+ *
+ * for (i = 0; i < mtd_pairing_groups(mtd); i++) {
+ *	info.pair = i;
+ *	mtd_pairing_info_to_wunit(mtd, &info);
+ *	...
+ * }
+ */
+int mtd_wunit_to_pairing_info(struct mtd_info *mtd, int wunit,
+			      struct mtd_pairing_info *info)
+{
+	int npairs = mtd_wunit_per_eb(mtd) / mtd_pairing_groups(mtd);
+
+	if (wunit < 0 || wunit >= npairs)
+		return -EINVAL;
+
+	if (mtd->pairing && mtd->pairing->get_info)
+		return mtd->pairing->get_info(mtd, wunit, info);
+
+	info->group = 0;
+	info->pair = wunit;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(mtd_wunit_to_pairing_info);
+
+/**
+ * mtd_wunit_to_pairing_info - get wunit from pairing information
+ * @mtd: pointer to new MTD device info structure
+ * @info: pairing information struct
+ *
+ * Returns a positive number representing the wunit associated to the info
+ * struct, or a negative error code.
+ *
+ * This is the reverse of mtd_wunit_to_pairing_info(), and can help one to
+ * iterate over all wunits of a given pair (see mtd_wunit_to_pairing_info()
+ * doc).
+ *
+ * It can also be used to only program the first page of each pair (i.e.
+ * page attached to group 0), which allows one to use an MLC NAND in
+ * software-emulated SLC mode:
+ *
+ * info.group = 0;
+ * npairs = mtd_wunit_per_eb(mtd) / mtd_pairing_groups(mtd);
+ * for (info.pair = 0; info.pair < npairs; info.pair++) {
+ *	wunit = mtd_pairing_info_to_wunit(mtd, &info);
+ *	mtd_write(mtd, mtd_wunit_to_offset(mtd, blkoffs, wunit),
+ *		  mtd->writesize, &retlen, buf + (i * mtd->writesize));
+ * }
+ */
+int mtd_pairing_info_to_wunit(struct mtd_info *mtd,
+			      const struct mtd_pairing_info *info)
+{
+	int ngroups = mtd_pairing_groups(mtd);
+	int npairs = mtd_wunit_per_eb(mtd) / ngroups;
+
+	if (!info || info->pair < 0 || info->pair >= npairs ||
+	    info->group < 0 || info->group >= ngroups)
+		return -EINVAL;
+
+	if (mtd->pairing && mtd->pairing->get_wunit)
+		return mtd->pairing->get_wunit(mtd, info);
+
+	return info->pair;
+}
+EXPORT_SYMBOL_GPL(mtd_pairing_info_to_wunit);
+
+/**
+ * mtd_pairing_groups - get the number of pairing groups
+ * @mtd: pointer to new MTD device info structure
+ *
+ * Returns the number of pairing groups.
+ *
+ * This number is usually equal to the number of bits exposed by a single
+ * cell, and can be used in conjunction with mtd_pairing_info_to_wunit()
+ * to iterate over all pages of a given pair.
+ */
+int mtd_pairing_groups(struct mtd_info *mtd)
+{
+	if (!mtd->pairing || !mtd->pairing->ngroups)
+		return 1;
+
+	return mtd->pairing->ngroups;
+}
+EXPORT_SYMBOL_GPL(mtd_pairing_groups);
+
 /**
 *	add_mtd_device - register an MTD device
 *	@mtd: pointer to new MTD device info structure
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@ -409,6 +409,7 @@ static struct mtd_part *allocate_partition(struct mtd_info *master,
 	slave->mtd.oobsize = master->oobsize;
 	slave->mtd.oobavail = master->oobavail;
 	slave->mtd.subpage_sft = master->subpage_sft;
+	slave->mtd.pairing = master->pairing;

 	slave->mtd.name = name;
 	slave->mtd.owner = master->owner;
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@ -127,6 +127,82 @@ struct mtd_ooblayout_ops {
 		    struct mtd_oob_region *oobfree);
 };

+/**
+ * struct mtd_pairing_info - page pairing information
+ *
+ * @pair: pair id
+ * @group: group id
+ *
+ * The term "pair" is used here, even though TLC NANDs might group pages by 3
+ * (3 bits in a single cell). A pair should regroup all pages that are sharing
+ * the same cell. Pairs are then indexed in ascending order.
+ *
+ * @group is defining the position of a page in a given pair. It can also be
+ * seen as the bit position in the cell: page attached to bit 0 belongs to
+ * group 0, page attached to bit 1 belongs to group 1, etc.
+ *
+ * Example:
+ * The H27UCG8T2BTR-BC datasheet describes the following pairing scheme:
+ *
+ *		group-0		group-1
+ *
+ *  pair-0	page-0		page-4
+ *  pair-1	page-1		page-5
+ *  pair-2	page-2		page-8
+ *  ...
+ *  pair-127	page-251	page-255
+ *
+ *
+ * Note that the "group" and "pair" terms were extracted from Samsung and
+ * Hynix datasheets, and might be referenced under other names in other
+ * datasheets (Micron is describing this concept as "shared pages").
+ */
+struct mtd_pairing_info {
+	int pair;
+	int group;
+};
+
+/**
+ * struct mtd_pairing_scheme - page pairing scheme description
+ *
+ * @ngroups: number of groups. Should be related to the number of bits
+ *	     per cell.
+ * @get_info: converts a write-unit (page number within an erase block) into
+ *	      mtd_pairing information (pair + group). This function should
+ *	      fill the info parameter based on the wunit index or return
+ *	      -EINVAL if the wunit parameter is invalid.
+ * @get_wunit: converts pairing information into a write-unit (page) number.
+ *	       This function should return the wunit index pointed by the
+ *	       pairing information described in the info argument. It should
+ *	       return -EINVAL, if there's no wunit corresponding to the
+ *	       passed pairing information.
+ *
+ * See mtd_pairing_info documentation for a detailed explanation of the
+ * pair and group concepts.
+ *
+ * The mtd_pairing_scheme structure provides a generic solution to represent
+ * NAND page pairing scheme. Instead of exposing two big tables to do the
+ * write-unit <-> (pair + group) conversions, we ask the MTD drivers to
+ * implement the ->get_info() and ->get_wunit() functions.
+ *
+ * MTD users will then be able to query these information by using the
+ * mtd_pairing_info_to_wunit() and mtd_wunit_to_pairing_info() helpers.
+ *
+ * @ngroups is here to help MTD users iterating over all the pages in a
+ * given pair. This value can be retrieved by MTD users using the
+ * mtd_pairing_groups() helper.
+ *
+ * Examples are given in the mtd_pairing_info_to_wunit() and
+ * mtd_wunit_to_pairing_info() documentation.
+ */
+struct mtd_pairing_scheme {
+	int ngroups;
+	int (*get_info)(struct mtd_info *mtd, int wunit,
+			struct mtd_pairing_info *info);
+	int (*get_wunit)(struct mtd_info *mtd,
+			 const struct mtd_pairing_info *info);
+};
+
 struct module;	/* only needed for owner field in mtd_info */

 struct mtd_info {
@ -188,6 +264,9 @@ struct mtd_info {
 	/* OOB layout description */
 	const struct mtd_ooblayout_ops *ooblayout;

+	/* NAND pairing scheme, only provided for MLC/TLC NANDs */
+	const struct mtd_pairing_scheme *pairing;
+
 	/* the ecc step size. */
 	unsigned int ecc_step_size;

@ -296,6 +375,12 @@ static inline void mtd_set_ooblayout(struct mtd_info *mtd,
 	mtd->ooblayout = ooblayout;
 }

+static inline void mtd_set_pairing_scheme(struct mtd_info *mtd,
+				const struct mtd_pairing_scheme *pairing)
+{
+	mtd->pairing = pairing;
+}
+
 static inline void mtd_set_of_node(struct mtd_info *mtd,
 				   struct device_node *np)
 {
@ -312,6 +397,11 @@ static inline int mtd_oobavail(struct mtd_info *mtd, struct mtd_oob_ops *ops)
 	return ops->mode == MTD_OPS_AUTO_OOB ? mtd->oobavail : mtd->oobsize;
 }

+int mtd_wunit_to_pairing_info(struct mtd_info *mtd, int wunit,
+			      struct mtd_pairing_info *info);
+int mtd_pairing_info_to_wunit(struct mtd_info *mtd,
+			      const struct mtd_pairing_info *info);
+int mtd_pairing_groups(struct mtd_info *mtd);
 int mtd_erase(struct mtd_info *mtd, struct erase_info *instr);
 int mtd_point(struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen,
 	      void **virt, resource_size_t *phys);
@ -397,6 +487,23 @@ static inline uint32_t mtd_mod_by_ws(uint64_t sz, struct mtd_info *mtd)
 	return do_div(sz, mtd->writesize);
 }

+static inline int mtd_wunit_per_eb(struct mtd_info *mtd)
+{
+	return mtd->erasesize / mtd->writesize;
+}
+
+static inline int mtd_offset_to_wunit(struct mtd_info *mtd, loff_t offs)
+{
+	return mtd_div_by_ws(mtd_mod_by_eb(offs, mtd), mtd);
+}
+
+static inline loff_t mtd_wunit_to_offset(struct mtd_info *mtd, loff_t base,
+					 int wunit)
+{
+	return base + (wunit * mtd->writesize);
+}
+
+
 static inline int mtd_has_oob(const struct mtd_info *mtd)
 {
 	return mtd->_read_oob && mtd->_write_oob;