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# SPDX-License-Identifier: GPL-2.0-only
menuconfig MTD_UBI
tristate "Enable UBI - Unsorted block images"
select CRC32
UBI is a software layer above MTD layer which admits use of LVM-like
logical volumes on top of MTD devices, hides some complexities of
flash chips like wear and bad blocks and provides some other useful
capabilities. Please, consult the MTD web site for more details
int "UBI wear-leveling threshold"
default 4096
range 2 65536
This parameter defines the maximum difference between the highest
erase counter value and the lowest erase counter value of eraseblocks
of UBI devices. When this threshold is exceeded, UBI starts performing
wear leveling by means of moving data from eraseblock with low erase
counter to eraseblocks with high erase counter.
The default value should be OK for SLC NAND flashes, NOR flashes and
other flashes which have eraseblock life-cycle 100000 or more.
However, in case of MLC NAND flashes which typically have eraseblock
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).
int "Maximum expected bad eraseblock count per 1024 eraseblocks"
default 20
range 0 768
This option specifies the maximum bad physical eraseblocks UBI
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.
This option can be overridden by the "mtd=" UBI module parameter or
by the "attach" ioctl.
Leave the default value if unsure.
bool "UBI Fastmap (Experimental feature)"
default n
Important: this feature is experimental so far and the on-flash
format for fastmap may change in the next kernel versions
Fastmap is a mechanism which allows attaching an UBI device
in nearly constant time. Instead of scanning the whole MTD device it
only has to locate a checkpoint (called fastmap) on the device.
The on-flash fastmap contains all information needed to attach
the device. Using fastmap makes only sense on large devices where
attaching by scanning takes long. UBI will not automatically install
a fastmap on old images, but you can set the UBI module parameter
fm_autoconvert to 1 if you want so. Please note that fastmap-enabled
images are still usable with UBI implementations without
fastmap support. On typical flash devices the whole fastmap fits
into one PEB. UBI will reserve PEBs to hold two fastmaps.
If in doubt, say "N".
tristate "MTD devices emulation driver (gluebi)"
This option enables gluebi - an additional driver which emulates MTD
devices on top of UBI volumes: for each UBI volumes an MTD device is
created, and all I/O to this MTD device is redirected to the UBI
volume. This is handy to make MTD-oriented software (like JFFS2)
work on top of UBI. Do not enable this unless you use legacy
bool "Read-only block devices on top of UBI volumes"
default n
depends on BLOCK
This option enables read-only UBI block devices support. UBI block
devices will be layered on top of UBI volumes, which means that the
UBI driver will transparently handle things like bad eraseblocks and
bit-flips. You can put any block-oriented file system on top of UBI
volumes in read-only mode (e.g., ext4), but it is probably most
practical for read-only file systems, like squashfs.
When selected, this feature will be built in the UBI driver.
If in doubt, say "N".
endif # MTD_UBI