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>
diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 3174dd4..ce311aa 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -607,8 +607,18 @@
 	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);