bc08b449ee
Instead of taking the spinlock, the lockless versions atomically check
that the lock is not taken, and do the reference count update using a
cmpxchg() loop. This is semantically identical to doing the reference
count update protected by the lock, but avoids the "wait for lock"
contention that you get when accesses to the reference count are
contended.
Note that a "lockref" is absolutely _not_ equivalent to an atomic_t.
Even when the lockref reference counts are updated atomically with
cmpxchg, the fact that they also verify the state of the spinlock means
that the lockless updates can never happen while somebody else holds the
spinlock.
So while "lockref_put_or_lock()" looks a lot like just another name for
"atomic_dec_and_lock()", and both optimize to lockless updates, they are
fundamentally different: the decrement done by atomic_dec_and_lock() is
truly independent of any lock (as long as it doesn't decrement to zero),
so a locked region can still see the count change.
The lockref structure, in contrast, really is a *locked* reference
count. If you hold the spinlock, the reference count will be stable and
you can modify the reference count without using atomics, because even
the lockless updates will see and respect the state of the lock.
In order to enable the cmpxchg lockless code, the architecture needs to
do three things:
(1) Make sure that the "arch_spinlock_t" and an "unsigned int" can fit
in an aligned u64, and have a "cmpxchg()" implementation that works
on such a u64 data type.
(2) define a helper function to test for a spinlock being unlocked
("arch_spin_value_unlocked()")
(3) select the "ARCH_USE_CMPXCHG_LOCKREF" config variable in its
Kconfig file.
This enables it for x86-64 (but not 32-bit, we'd need to make sure
cmpxchg() turns into the proper cmpxchg8b in order to enable it for
32-bit mode).
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
439 lines
9.5 KiB
Plaintext
439 lines
9.5 KiB
Plaintext
#
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# Library configuration
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#
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config BINARY_PRINTF
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def_bool n
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menu "Library routines"
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config RAID6_PQ
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tristate
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config BITREVERSE
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tristate
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config RATIONAL
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boolean
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config GENERIC_STRNCPY_FROM_USER
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bool
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config GENERIC_STRNLEN_USER
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bool
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config GENERIC_NET_UTILS
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bool
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config GENERIC_FIND_FIRST_BIT
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bool
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config NO_GENERIC_PCI_IOPORT_MAP
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bool
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config GENERIC_PCI_IOMAP
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bool
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config GENERIC_IOMAP
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bool
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select GENERIC_PCI_IOMAP
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config GENERIC_IO
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boolean
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default n
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config STMP_DEVICE
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bool
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config PERCPU_RWSEM
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boolean
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config ARCH_USE_CMPXCHG_LOCKREF
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bool
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config CMPXCHG_LOCKREF
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def_bool y if ARCH_USE_CMPXCHG_LOCKREF
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depends on SMP
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depends on !GENERIC_LOCKBREAK
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depends on !DEBUG_SPINLOCK
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depends on !DEBUG_LOCK_ALLOC
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config CRC_CCITT
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tristate "CRC-CCITT functions"
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help
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This option is provided for the case where no in-kernel-tree
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modules require CRC-CCITT functions, but a module built outside
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the kernel tree does. Such modules that use library CRC-CCITT
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functions require M here.
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config CRC16
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tristate "CRC16 functions"
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help
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This option is provided for the case where no in-kernel-tree
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modules require CRC16 functions, but a module built outside
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the kernel tree does. Such modules that use library CRC16
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functions require M here.
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config CRC_T10DIF
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tristate "CRC calculation for the T10 Data Integrity Field"
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help
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This option is only needed if a module that's not in the
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kernel tree needs to calculate CRC checks for use with the
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SCSI data integrity subsystem.
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config CRC_ITU_T
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tristate "CRC ITU-T V.41 functions"
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help
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This option is provided for the case where no in-kernel-tree
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modules require CRC ITU-T V.41 functions, but a module built outside
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the kernel tree does. Such modules that use library CRC ITU-T V.41
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functions require M here.
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config CRC32
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tristate "CRC32/CRC32c functions"
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default y
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select BITREVERSE
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help
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This option is provided for the case where no in-kernel-tree
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modules require CRC32/CRC32c functions, but a module built outside
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the kernel tree does. Such modules that use library CRC32/CRC32c
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functions require M here.
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config CRC32_SELFTEST
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bool "CRC32 perform self test on init"
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default n
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depends on CRC32
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help
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This option enables the CRC32 library functions to perform a
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self test on initialization. The self test computes crc32_le
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and crc32_be over byte strings with random alignment and length
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and computes the total elapsed time and number of bytes processed.
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choice
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prompt "CRC32 implementation"
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depends on CRC32
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default CRC32_SLICEBY8
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help
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This option allows a kernel builder to override the default choice
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of CRC32 algorithm. Choose the default ("slice by 8") unless you
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know that you need one of the others.
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config CRC32_SLICEBY8
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bool "Slice by 8 bytes"
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help
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Calculate checksum 8 bytes at a time with a clever slicing algorithm.
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This is the fastest algorithm, but comes with a 8KiB lookup table.
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Most modern processors have enough cache to hold this table without
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thrashing the cache.
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This is the default implementation choice. Choose this one unless
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you have a good reason not to.
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config CRC32_SLICEBY4
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bool "Slice by 4 bytes"
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help
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Calculate checksum 4 bytes at a time with a clever slicing algorithm.
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This is a bit slower than slice by 8, but has a smaller 4KiB lookup
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table.
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Only choose this option if you know what you are doing.
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config CRC32_SARWATE
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bool "Sarwate's Algorithm (one byte at a time)"
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help
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Calculate checksum a byte at a time using Sarwate's algorithm. This
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is not particularly fast, but has a small 256 byte lookup table.
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Only choose this option if you know what you are doing.
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config CRC32_BIT
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bool "Classic Algorithm (one bit at a time)"
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help
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Calculate checksum one bit at a time. This is VERY slow, but has
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no lookup table. This is provided as a debugging option.
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Only choose this option if you are debugging crc32.
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endchoice
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config CRC7
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tristate "CRC7 functions"
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help
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This option is provided for the case where no in-kernel-tree
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modules require CRC7 functions, but a module built outside
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the kernel tree does. Such modules that use library CRC7
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functions require M here.
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config LIBCRC32C
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tristate "CRC32c (Castagnoli, et al) Cyclic Redundancy-Check"
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select CRYPTO
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select CRYPTO_CRC32C
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help
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This option is provided for the case where no in-kernel-tree
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modules require CRC32c functions, but a module built outside the
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kernel tree does. Such modules that use library CRC32c functions
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require M here. See Castagnoli93.
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Module will be libcrc32c.
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config CRC8
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tristate "CRC8 function"
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help
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This option provides CRC8 function. Drivers may select this
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when they need to do cyclic redundancy check according CRC8
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algorithm. Module will be called crc8.
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config AUDIT_GENERIC
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bool
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depends on AUDIT && !AUDIT_ARCH
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default y
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#
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# compression support is select'ed if needed
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#
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config ZLIB_INFLATE
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tristate
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config ZLIB_DEFLATE
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tristate
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config LZO_COMPRESS
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tristate
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config LZO_DECOMPRESS
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tristate
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config LZ4_COMPRESS
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tristate
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config LZ4HC_COMPRESS
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tristate
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config LZ4_DECOMPRESS
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tristate
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source "lib/xz/Kconfig"
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#
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# These all provide a common interface (hence the apparent duplication with
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# ZLIB_INFLATE; DECOMPRESS_GZIP is just a wrapper.)
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#
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config DECOMPRESS_GZIP
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select ZLIB_INFLATE
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tristate
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config DECOMPRESS_BZIP2
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tristate
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config DECOMPRESS_LZMA
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tristate
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config DECOMPRESS_XZ
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select XZ_DEC
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tristate
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config DECOMPRESS_LZO
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select LZO_DECOMPRESS
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tristate
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config DECOMPRESS_LZ4
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select LZ4_DECOMPRESS
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tristate
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#
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# Generic allocator support is selected if needed
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#
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config GENERIC_ALLOCATOR
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boolean
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#
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# reed solomon support is select'ed if needed
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#
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config REED_SOLOMON
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tristate
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config REED_SOLOMON_ENC8
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boolean
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config REED_SOLOMON_DEC8
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boolean
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config REED_SOLOMON_ENC16
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boolean
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config REED_SOLOMON_DEC16
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boolean
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#
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# BCH support is selected if needed
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#
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config BCH
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tristate
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config BCH_CONST_PARAMS
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boolean
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help
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Drivers may select this option to force specific constant
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values for parameters 'm' (Galois field order) and 't'
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(error correction capability). Those specific values must
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be set by declaring default values for symbols BCH_CONST_M
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and BCH_CONST_T.
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Doing so will enable extra compiler optimizations,
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improving encoding and decoding performance up to 2x for
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usual (m,t) values (typically such that m*t < 200).
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When this option is selected, the BCH library supports
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only a single (m,t) configuration. This is mainly useful
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for NAND flash board drivers requiring known, fixed BCH
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parameters.
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config BCH_CONST_M
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int
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range 5 15
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help
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Constant value for Galois field order 'm'. If 'k' is the
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number of data bits to protect, 'm' should be chosen such
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that (k + m*t) <= 2**m - 1.
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Drivers should declare a default value for this symbol if
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they select option BCH_CONST_PARAMS.
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config BCH_CONST_T
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int
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help
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Constant value for error correction capability in bits 't'.
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Drivers should declare a default value for this symbol if
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they select option BCH_CONST_PARAMS.
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#
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# Textsearch support is select'ed if needed
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#
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config TEXTSEARCH
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boolean
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config TEXTSEARCH_KMP
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tristate
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config TEXTSEARCH_BM
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tristate
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config TEXTSEARCH_FSM
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tristate
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config BTREE
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boolean
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config HAS_IOMEM
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boolean
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depends on !NO_IOMEM
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select GENERIC_IO
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default y
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config HAS_IOPORT
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boolean
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depends on HAS_IOMEM && !NO_IOPORT
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default y
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config HAS_DMA
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boolean
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depends on !NO_DMA
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default y
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config CHECK_SIGNATURE
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bool
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config CPUMASK_OFFSTACK
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bool "Force CPU masks off stack" if DEBUG_PER_CPU_MAPS
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help
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Use dynamic allocation for cpumask_var_t, instead of putting
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them on the stack. This is a bit more expensive, but avoids
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stack overflow.
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config DISABLE_OBSOLETE_CPUMASK_FUNCTIONS
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bool "Disable obsolete cpumask functions" if DEBUG_PER_CPU_MAPS
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depends on BROKEN
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config CPU_RMAP
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bool
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depends on SMP
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config DQL
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bool
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#
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# Netlink attribute parsing support is select'ed if needed
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#
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config NLATTR
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bool
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#
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# Generic 64-bit atomic support is selected if needed
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#
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config GENERIC_ATOMIC64
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bool
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config ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
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def_bool y if GENERIC_ATOMIC64
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config LRU_CACHE
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tristate
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config AVERAGE
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bool "Averaging functions"
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help
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This option is provided for the case where no in-kernel-tree
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modules require averaging functions, but a module built outside
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the kernel tree does. Such modules that use library averaging
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functions require Y here.
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If unsure, say N.
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config CLZ_TAB
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bool
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config CORDIC
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tristate "CORDIC algorithm"
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help
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This option provides an implementation of the CORDIC algorithm;
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calculations are in fixed point. Module will be called cordic.
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config DDR
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bool "JEDEC DDR data"
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help
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Data from JEDEC specs for DDR SDRAM memories,
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particularly the AC timing parameters and addressing
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information. This data is useful for drivers handling
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DDR SDRAM controllers.
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config MPILIB
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tristate
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select CLZ_TAB
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help
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Multiprecision maths library from GnuPG.
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It is used to implement RSA digital signature verification,
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which is used by IMA/EVM digital signature extension.
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config SIGNATURE
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tristate
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depends on KEYS && CRYPTO
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select CRYPTO_SHA1
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select MPILIB
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help
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Digital signature verification. Currently only RSA is supported.
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Implementation is done using GnuPG MPI library
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#
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# libfdt files, only selected if needed.
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#
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config LIBFDT
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bool
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config OID_REGISTRY
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tristate
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help
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Enable fast lookup object identifier registry.
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config UCS2_STRING
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tristate
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source "lib/fonts/Kconfig"
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endmenu
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