[PATCH] UBI: use a config value for default BEB limit

[Richard Genoud <richard.genoud@gmail.com>]

This patch provides the possibility to adjust the default value for
"maximum expected number of bad blocks per 1024 blocks" from kernel
configuration.

sam9_l9260_defconfig has been adjusted as well. The nand device used by
this card has a NVB of 3996/4096 ie a MAX_BEB_LIMIT of 25/1024

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
---
 arch/arm/configs/sam9_l9260_defconfig |    1 +
 drivers/mtd/ubi/Kconfig               |   29 +++++++++++++++++++++++++++++
 drivers/mtd/ubi/ubi.h                 |    2 +-
 3 files changed, 31 insertions(+), 1 deletions(-)

diff --git a/arch/arm/configs/sam9_l9260_defconfig b/arch/arm/configs/sam9_l9260_defconfig
index 47dd71a..2c20c9e 100644
--- a/arch/arm/configs/sam9_l9260_defconfig
+++ b/arch/arm/configs/sam9_l9260_defconfig
@@ -39,6 +39,7 @@ CONFIG_MTD_NAND=y
 CONFIG_MTD_NAND_ATMEL=y
 CONFIG_MTD_NAND_PLATFORM=y
 CONFIG_MTD_UBI=y
+CONFIG_MTD_UBI_DEFAULT_BEB_LIMIT=25
 CONFIG_MTD_UBI_GLUEBI=y
 CONFIG_BLK_DEV_LOOP=y
 CONFIG_BLK_DEV_RAM=y
diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index 7a57cc0..30e8370 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -27,6 +27,35 @@ config MTD_UBI_WL_THRESHOLD
 	  life-cycle less than 10000, the threshold should be lessened (e.g.,
 	  to 128 or 256, although it does not have to be power of 2).
 
+config MTD_UBI_DEFAULT_BEB_LIMIT
+	int "Maximum expected bad eraseblock count per 1024 eraseblocks"
+	default 20
+	range 0 256
+	help
+	  This option specifies the default value for maximum bad physical
+	  eraseblocks UBI expects on the MTD device (per 1024 eraseblocks).
+	  It will be used when the maximum bad PEB value is null in the
+	  UBI_IOCATT ioctl (e.g. when calling ubiattach) or in the kernel
+	  parameter ubi.mtd.
+	  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 that admits a 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
 	tristate "MTD devices emulation driver (gluebi)"
 	help
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index f926343..39a1e7e 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -51,7 +51,7 @@
 #define UBI_NAME_STR "ubi"
 
 /* Default number of maximum expected bad blocks per 1024 eraseblocks */
-#define MTD_UBI_DEFAULT_BEB_LIMIT 20
+#define MTD_UBI_DEFAULT_BEB_LIMIT CONFIG_MTD_UBI_DEFAULT_BEB_LIMIT
 
 /* Normal UBI messages */
 #define ubi_msg(fmt, ...) printk(KERN_NOTICE "UBI: " fmt "\n", ##__VA_ARGS__)
-- 
1.7.2.5