1 files changed, 21 insertions, 6 deletions

diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index b2f4f0f032f1..dcbaae3ead63 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -28,14 +28,29 @@ config MTD_UBI_WL_THRESHOLD
           to 128 or 256, although it does not have to be power of 2).
 
 config MTD_UBI_BEB_LIMIT
-        int "Percentage of maximum expected bad eraseblocks"
-        default 2
-        range 0 25
+        int "Maximum expected bad eraseblock count per 1024 eraseblocks"
+        default 20
+        range 0 768
         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.
+          expects on the MTD device (per 1024 eraseblocks). If the underlying
+          flash does not admit of bad eraseblocks (e.g. NOR flash), this value
+          is ignored.
+
+          NAND datasheets often specify the minimum and maximum NVM (Number of
+          Valid Blocks) for the flashes' endurance lifetime. The maximum
+          expected bad eraseblocks per 1024 eraseblocks then can be calculated
+          as "1024 * (1 - MinNVB / MaxNVB)", which gives 20 for most NANDs
+          (MaxNVB is basically the total count of eraseblocks on the chip).
+
+          To put it differently, if this value is 20, UBI will try to reserve
+          about 1.9% of physical eraseblocks for bad blocks handling. And that
+          will be 1.9% of eraseblocks on the entire NAND chip, not just the MTD
+          partition UBI attaches. This means that if you have, say, a NAND
+          flash chip admits maximum 40 bad eraseblocks, and it is split on two
+          MTD partitions of the same size, UBI will reserve 40 eraseblocks when
+          attaching a partition.
+
           Leave the default value if unsure.
 
 config MTD_UBI_GLUEBI