106 lines
4.4 KiB
Text
106 lines
4.4 KiB
Text
menuconfig MTD_UBI
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tristate "Enable UBI - Unsorted block images"
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select CRC32
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help
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UBI is a software layer above MTD layer which admits use of LVM-like
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logical volumes on top of MTD devices, hides some complexities of
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flash chips like wear and bad blocks and provides some other useful
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capabilities. Please, consult the MTD web site for more details
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(www.linux-mtd.infradead.org).
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if MTD_UBI
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config MTD_UBI_WL_THRESHOLD
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int "UBI wear-leveling threshold"
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default 4096
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range 2 65536
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help
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This parameter defines the maximum difference between the highest
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erase counter value and the lowest erase counter value of eraseblocks
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of UBI devices. When this threshold is exceeded, UBI starts performing
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wear leveling by means of moving data from eraseblock with low erase
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counter to eraseblocks with high erase counter.
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The default value should be OK for SLC NAND flashes, NOR flashes and
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other flashes which have eraseblock life-cycle 100000 or more.
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However, in case of MLC NAND flashes which typically have eraseblock
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life-cycle less than 10000, the threshold should be lessened (e.g.,
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to 128 or 256, although it does not have to be power of 2).
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config MTD_UBI_BEB_LIMIT
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int "Maximum expected bad eraseblock count per 1024 eraseblocks"
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default 20
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range 0 768
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help
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This option specifies the maximum bad physical eraseblocks UBI
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expects on the MTD device (per 1024 eraseblocks). If the underlying
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flash does not admit of bad eraseblocks (e.g. NOR flash), this value
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is ignored.
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NAND datasheets often specify the minimum and maximum NVM (Number of
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Valid Blocks) for the flashes' endurance lifetime. The maximum
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expected bad eraseblocks per 1024 eraseblocks then can be calculated
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as "1024 * (1 - MinNVB / MaxNVB)", which gives 20 for most NANDs
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(MaxNVB is basically the total count of eraseblocks on the chip).
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To put it differently, if this value is 20, UBI will try to reserve
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about 1.9% of physical eraseblocks for bad blocks handling. And that
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will be 1.9% of eraseblocks on the entire NAND chip, not just the MTD
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partition UBI attaches. This means that if you have, say, a NAND
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flash chip admits maximum 40 bad eraseblocks, and it is split on two
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MTD partitions of the same size, UBI will reserve 40 eraseblocks when
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attaching a partition.
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This option can be overridden by the "mtd=" UBI module parameter or
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by the "attach" ioctl.
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Leave the default value if unsure.
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config MTD_UBI_FASTMAP
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bool "UBI Fastmap (Experimental feature)"
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default n
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help
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Important: this feature is experimental so far and the on-flash
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format for fastmap may change in the next kernel versions
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Fastmap is a mechanism which allows attaching an UBI device
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in nearly constant time. Instead of scanning the whole MTD device it
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only has to locate a checkpoint (called fastmap) on the device.
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The on-flash fastmap contains all information needed to attach
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the device. Using fastmap makes only sense on large devices where
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attaching by scanning takes long. UBI will not automatically install
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a fastmap on old images, but you can set the UBI module parameter
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fm_autoconvert to 1 if you want so. Please note that fastmap-enabled
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images are still usable with UBI implementations without
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fastmap support. On typical flash devices the whole fastmap fits
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into one PEB. UBI will reserve PEBs to hold two fastmaps.
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If in doubt, say "N".
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config MTD_UBI_GLUEBI
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tristate "MTD devices emulation driver (gluebi)"
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help
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This option enables gluebi - an additional driver which emulates MTD
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devices on top of UBI volumes: for each UBI volumes an MTD device is
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created, and all I/O to this MTD device is redirected to the UBI
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volume. This is handy to make MTD-oriented software (like JFFS2)
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work on top of UBI. Do not enable this unless you use legacy
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software.
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config MTD_UBI_BLOCK
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bool "Read-only block devices on top of UBI volumes"
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default n
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depends on BLOCK
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help
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This option enables read-only UBI block devices support. UBI block
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devices will be layered on top of UBI volumes, which means that the
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UBI driver will transparently handle things like bad eraseblocks and
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bit-flips. You can put any block-oriented file system on top of UBI
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volumes in read-only mode (e.g., ext4), but it is probably most
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practical for read-only file systems, like squashfs.
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When selected, this feature will be built in the UBI driver.
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If in doubt, say "N".
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endif # MTD_UBI
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