xref: /openbmc/linux/drivers/mtd/ubi/Kconfig (revision 93d90ad7)
1menuconfig 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
11if MTD_UBI
12
13config 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
30config 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
59config 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
80config 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
90config 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
106endif # MTD_UBI
107