3 files changed, 18 insertions, 3 deletions

diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index 3e185e46cf6c..271a842f8c39 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -51,7 +51,8 @@ config MTD_UBI_BEB_LIMIT
           MTD partitions of the same size, UBI will reserve 40 eraseblocks when
           attaching a partition.
 
-          This option can be overridden by the "mtd=" UBI module parameter.
+          This option can be overridden by the "mtd=" UBI module parameter or
+          by the "attach" ioctl.
 
           Leave the default value if unsure.
 
diff --git a/drivers/mtd/ubi/cdev.c b/drivers/mtd/ubi/cdev.c
index 619f9144f990..7885dc0934ce 100644
--- a/drivers/mtd/ubi/cdev.c
+++ b/drivers/mtd/ubi/cdev.c
@@ -1011,7 +1011,7 @@ static long ctrl_cdev_ioctl(struct file *file, unsigned int cmd,
                  */
                 mutex_lock(&ubi_devices_mutex);
                 err = ubi_attach_mtd_dev(mtd, req.ubi_num, req.vid_hdr_offset,
-                                         CONFIG_MTD_UBI_BEB_LIMIT);
+                                         req.max_beb_per1024);
                 mutex_unlock(&ubi_devices_mutex);
                 if (err < 0)
                         put_mtd_device(mtd);
diff --git a/include/mtd/ubi-user.h b/include/mtd/ubi-user.h
index 8787349fbafe..53cae1e11e57 100644
--- a/include/mtd/ubi-user.h
+++ b/include/mtd/ubi-user.h
@@ -222,6 +222,7 @@ enum {
  * @ubi_num: UBI device number to create
  * @mtd_num: MTD device number to attach
  * @vid_hdr_offset: VID header offset (use defaults if %0)
+ * @max_beb_per1024: maximum expected number of bad PEB per 1024 PEBs
  * @padding: reserved for future, not used, has to be zeroed
  *
  * This data structure is used to specify MTD device UBI has to attach and the
@@ -245,12 +246,25 @@ enum {
  * be 2KiB-64 bytes = 1984. Note, that this position is not even 512-bytes
  * aligned, which is OK, as UBI is clever enough to realize this is 4th
  * sub-page of the first page and add needed padding.
+ *
+ * The @max_beb_per1024 is the maximum amount of bad PEBs UBI expects on the
+ * UBI device per 1024 eraseblocks.  This value is often given in an other form
+ * in the NAND datasheet (min NVB i.e. minimal number of valid blocks). The
+ * maximum expected bad eraseblocks per 1024 is then:
+ *    1024 * (1 - MinNVB / MaxNVB)
+ * Which gives 20 for most NAND devices.  This limit is used in order to derive
+ * amount of eraseblock UBI reserves for handling new bad blocks. If the device
+ * has more bad eraseblocks than this limit, UBI does not reserve any physical
+ * eraseblocks for new bad eraseblocks, but attempts to use available
+ * eraseblocks (if any). The accepted range is 0-768. If 0 is given, the
+ * default kernel value of %CONFIG_MTD_UBI_BEB_LIMIT will be used.
  */
 struct ubi_attach_req {
         __s32 ubi_num;
         __s32 mtd_num;
         __s32 vid_hdr_offset;
-        __s8 padding[12];
+        __s16 max_beb_per1024;
+        __s8 padding[10];
 };
 
 /**