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Edit File: Kconfig

# SPDX-License-Identifier: GPL-2.0-only menuconfig MTD_UBI tristate "Enable UBI - Unsorted block images" select CRC32 help 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 (www.linux-mtd.infradead.org). if MTD_UBI config MTD_UBI_WL_THRESHOLD int "UBI wear-leveling threshold" default 4096 range 2 65536 help 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). config MTD_UBI_BEB_LIMIT int "Maximum expected bad eraseblock count per 1024 eraseblocks" default 20 range 0 768 help 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. config MTD_UBI_FASTMAP bool "UBI Fastmap (Experimental feature)" default n help 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". config MTD_UBI_GLUEBI tristate "MTD devices emulation driver (gluebi)" help 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 software. config MTD_UBI_BLOCK bool "Read-only block devices on top of UBI volumes" default n depends on BLOCK help 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