UBI: introduce new bad PEB limit

Introduce 'ubi->bad_peb_limit', which specifies an upper limit of PEBs
UBI expects to go bad.  Currently, it is initialized to a fixed percentage
of total PEBs in the UBI device (configurable via CONFIG_MTD_UBI_BEB_LIMIT).

The 'bad_peb_limit' is intended to be used for calculating the amount of PEBs
UBI needs to reserve for bad eraseblock handling.

Artem: minor amendments.
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>

drivers/mtd/ubi/Kconfig

@@ -34,13 +34,25 @@ config MTD_UBI_BEB_RESERVE
 	help
 	  If the MTD device admits of bad eraseblocks (e.g. NAND flash), UBI
 	  reserves some amount of physical eraseblocks to handle new bad
-	  eraseblocks. For example, if a flash physical eraseblock becomes bad,
-	  UBI uses these reserved physical eraseblocks to relocate the bad one.
-	  This option specifies how many physical eraseblocks will be reserved
-	  for bad eraseblock handling (percents of total number of good flash
-	  eraseblocks). If the underlying flash does not admit of bad
-	  eraseblocks (e.g. NOR flash), this value is ignored and nothing is
-	  reserved. Leave the default value if unsure.
+	  eraseblocks. When a physical eraseblock becomes bad, UBI uses these
+	  reserved physical eraseblocks to relocate the bad one. This
+	  configuration option specifies how many physical eraseblocks will be
+	  reserved for bad eraseblock handling (percents of total number of
+	  good physical eraseblocks on this MTD partition). If the underlying
+	  flash does not admit of bad eraseblocks (e.g. NOR flash), this value
+	  is ignored and nothing is reserved. Leave the default value if
+	  unsure.
+
+config MTD_UBI_BEB_LIMIT
+	int "Percentage of maximum expected bad eraseblocks"
+	default 2
+	range 0 25
+	help
+	  This option specifies the maximum bad physical eraseblocks UBI
+	  expects on the UBI device (percents of total number of physical
+	  eraseblocks on this MTD partition). If the underlying flash does not
+	  admit of bad eraseblocks (e.g. NOR flash), this value is ignored.
+	  Leave the default value if unsure.
 
 config MTD_UBI_GLUEBI
 	tristate "MTD devices emulation driver (gluebi)"

drivers/mtd/ubi/build.c

@@ -607,8 +607,18 @@ static int io_init(struct ubi_device *ubi)
 	ubi->peb_count  = mtd_div_by_eb(ubi->mtd->size, ubi->mtd);
 	ubi->flash_size = ubi->mtd->size;
 
-	if (mtd_can_have_bb(ubi->mtd))
+	if (mtd_can_have_bb(ubi->mtd)) {
 		ubi->bad_allowed = 1;
+		if (CONFIG_MTD_UBI_BEB_LIMIT > 0) {
+			int percent = CONFIG_MTD_UBI_BEB_LIMIT;
+			int limit = mult_frac(ubi->peb_count, percent, 100);
+
+			/* Round it up */
+			if (mult_frac(limit, 100, percent) < ubi->peb_count)
+				limit += 1;
+			ubi->bad_peb_limit = limit;
+		}
+	}
 
 	if (ubi->mtd->type == MTD_NORFLASH) {
 		ubi_assert(ubi->mtd->writesize == 1);

drivers/mtd/ubi/ubi.h

@@ -363,6 +363,7 @@ struct ubi_wl_entry;
  * @flash_size: underlying MTD device size (in bytes)
  * @peb_count: count of physical eraseblocks on the MTD device
  * @peb_size: physical eraseblock size
+ * @bad_peb_limit: top limit of expected bad physical eraseblocks
  * @bad_peb_count: count of bad physical eraseblocks
  * @good_peb_count: count of good physical eraseblocks
  * @corr_peb_count: count of corrupted physical eraseblocks (preserved and not
@@ -410,6 +411,7 @@ struct ubi_device {
 	int avail_pebs;
 	int beb_rsvd_pebs;
 	int beb_rsvd_level;
+	int bad_peb_limit;
 
 	int autoresize_vol_id;
 	int vtbl_slots;