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Linux/drivers/mtd/ubi/Kconfig

  1 menuconfig MTD_UBI
  2         tristate "Enable UBI - Unsorted block images"
  3         select CRC32
  4         help
  5           UBI is a software layer above MTD layer which admits of LVM-like
  6           logical volumes on top of MTD devices, hides some complexities of
  7           flash chips like wear and bad blocks and provides some other useful
  8           capabilities. Please, consult the MTD web site for more details
  9           (www.linux-mtd.infradead.org).
 10 
 11 if MTD_UBI
 12 
 13 config MTD_UBI_WL_THRESHOLD
 14         int "UBI wear-leveling threshold"
 15         default 4096
 16         range 2 65536
 17         help
 18           This parameter defines the maximum difference between the highest
 19           erase counter value and the lowest erase counter value of eraseblocks
 20           of UBI devices. When this threshold is exceeded, UBI starts performing
 21           wear leveling by means of moving data from eraseblock with low erase
 22           counter to eraseblocks with high erase counter.
 23 
 24           The default value should be OK for SLC NAND flashes, NOR flashes and
 25           other flashes which have eraseblock life-cycle 100000 or more.
 26           However, in case of MLC NAND flashes which typically have eraseblock
 27           life-cycle less than 10000, the threshold should be lessened (e.g.,
 28           to 128 or 256, although it does not have to be power of 2).
 29 
 30 config MTD_UBI_BEB_LIMIT
 31         int "Maximum expected bad eraseblock count per 1024 eraseblocks"
 32         default 20
 33         range 0 768
 34         help
 35           This option specifies the maximum bad physical eraseblocks UBI
 36           expects on the MTD device (per 1024 eraseblocks). If the underlying
 37           flash does not admit of bad eraseblocks (e.g. NOR flash), this value
 38           is ignored.
 39 
 40           NAND datasheets often specify the minimum and maximum NVM (Number of
 41           Valid Blocks) for the flashes' endurance lifetime. The maximum
 42           expected bad eraseblocks per 1024 eraseblocks then can be calculated
 43           as "1024 * (1 - MinNVB / MaxNVB)", which gives 20 for most NANDs
 44           (MaxNVB is basically the total count of eraseblocks on the chip).
 45 
 46           To put it differently, if this value is 20, UBI will try to reserve
 47           about 1.9% of physical eraseblocks for bad blocks handling. And that
 48           will be 1.9% of eraseblocks on the entire NAND chip, not just the MTD
 49           partition UBI attaches. This means that if you have, say, a NAND
 50           flash chip admits maximum 40 bad eraseblocks, and it is split on two
 51           MTD partitions of the same size, UBI will reserve 40 eraseblocks when
 52           attaching a partition.
 53 
 54           This option can be overridden by the "mtd=" UBI module parameter or
 55           by the "attach" ioctl.
 56 
 57           Leave the default value if unsure.
 58 
 59 config MTD_UBI_FASTMAP
 60         bool "UBI Fastmap (Experimental feature)"
 61         default n
 62         help
 63            Important: this feature is experimental so far and the on-flash
 64            format for fastmap may change in the next kernel versions
 65 
 66            Fastmap is a mechanism which allows attaching an UBI device
 67            in nearly constant time. Instead of scanning the whole MTD device it
 68            only has to locate a checkpoint (called fastmap) on the device.
 69            The on-flash fastmap contains all information needed to attach
 70            the device. Using fastmap makes only sense on large devices where
 71            attaching by scanning takes long. UBI will not automatically install
 72            a fastmap on old images, but you can set the UBI module parameter
 73            fm_autoconvert to 1 if you want so. Please note that fastmap-enabled
 74            images are still usable with UBI implementations without
 75            fastmap support. On typical flash devices the whole fastmap fits
 76            into one PEB. UBI will reserve PEBs to hold two fastmaps.
 77 
 78            If in doubt, say "N".
 79 
 80 config MTD_UBI_GLUEBI
 81         tristate "MTD devices emulation driver (gluebi)"
 82         help
 83            This option enables gluebi - an additional driver which emulates MTD
 84            devices on top of UBI volumes: for each UBI volumes an MTD device is
 85            created, and all I/O to this MTD device is redirected to the UBI
 86            volume. This is handy to make MTD-oriented software (like JFFS2)
 87            work on top of UBI. Do not enable this unless you use legacy
 88            software.
 89 
 90 config MTD_UBI_BLOCK
 91         bool "Read-only block devices on top of UBI volumes"
 92         default n
 93         depends on BLOCK
 94         help
 95            This option enables read-only UBI block devices support. UBI block
 96            devices will be layered on top of UBI volumes, which means that the
 97            UBI driver will transparently handle things like bad eraseblocks and
 98            bit-flips. You can put any block-oriented file system on top of UBI
 99            volumes in read-only mode (e.g., ext4), but it is probably most
100            practical for read-only file systems, like squashfs.
101 
102            When selected, this feature will be built in the UBI driver.
103 
104            If in doubt, say "N".
105 
106 endif # MTD_UBI

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