29 

    30 	General purpose atomic operations and utility functions

    31 	All functions in this header are available on both user and kernel side.

    32 

    33 Atomic operations:

    34 	__e32_atomic_xxx_yyy8() should be used for 8 bit atomic variables

    35 	__e32_atomic_xxx_yyy16() should be used for 16 bit atomic variables

    36 	__e32_atomic_xxx_yyy32() should be used for 32 bit atomic variables

    37 	__e32_atomic_xxx_yyy64() should be used for 64 bit atomic variables

    38 	__e32_atomic_xxx_yyy_ptr() should be used for atomic updates to pointers

    39 

    40 	xxx specifies the operation performed

    41 		load	read memory atomically

    42 		store	write memory atomically

    43 		swp		write to a memory location and return the original value of the

    44 				memory location

    45 		add		add a value to a memory location and return the original value

    46 				of the memory location

    47 		and		bitwise AND a value with a memory location and return the

    48 				original value of the memory location

    49 		ior		bitwise OR a value with a memory location and return the

    50 				original value of the memory location

    51 		xor		bitwise XOR a value with a memory location and return the

    52 				original value of the memory location

    53 		axo		atomic { orig_v = *p; *p = (orig_v & u) ^ v; } return orig_v;

    54 		cas		if the value of a memory location matches a specified expected

    55 				value, write a specified new value and return TRUE, otherwise

    56 				update the expected value with the actual value seen and return

    57 				FALSE.

    58 		tau		if the value of a memory location is >= a specified threshold,

    59 				considered as an unsigned integer, add a specified value to it

    60 				otherwise add a different specified	value to it; return the

    61 				original value of the memory location

    62 		tas		if the value of a memory location is >= a specified threshold,

    63 				considered as a signed integer, add a specified value to it

    64 				otherwise add a different specified	value to it; return the

    65 				original value of the memory location

    66 				

    67 	yyy specifies the memory ordering:

    68 		rlx = relaxed memory ordering

    69 				there is no guarantee on the order in which the atomic operation

    70 				is observed relative to preceding or following memory accesses

    71 		acq = acquire semantics

    72 				the atomic operation is guaranteed to be observed before any

    73 				following memory accesses

    74 		rel = release semantics

    75 				the atomic operation is guaranteed to be observed after any

    76 				preceding memory accesses

    77 		ord = fully ordered

    78 				the atomic operation is guaranteed to be observed after any

    79 				preceding memory accesses and before any following memory

    80 				accesses

    81 

    82 	Note that these operations should only be used on normal memory regions

    83 	since they are implemented in terms of LDREX/STREX and so multiple reads

    84 	can occur before the operation completes. Also __e32_atomic_load_yyy64()

    85 	can't be used on read-only memory regions since it uses LDREXD/STREXD to

    86 	guarantee atomicity.

    87 	Atomic operations may only be used on naturally aligned memory (i.e. *16()

    88 	operations on an even address, *32() operations on an address which is a

    89 	multiple of 4 and *64() operations on an address which is a multiple of 8).

    90 	This applies even if you have (unwisely) decided to turn off alignment

    91 	checking.

    92 

    93 Barrier operations:

    94 	Two barrier functions are provided:

    95 	__e32_memory_barrier() - this ensures all preceding explicit memory accesses

    96 				are observed before any following explicit memory accesses.

    97 				Equates to the ARM DMB instruction.

    98 	__e32_io_completion_barrier() - this ensures all preceding explicit memory

    99 				accesses complete before any following instructions execute.

   100 				For example, it ensures that writes to I/O devices have actually

   101 				occurred before execution continues.

   102 				Equates to the ARM DSB instruction.

   103 

   104 Utility functions:

   105 	__e32_find_ms1_32	Return bit position of most significant 1 in a 32 bit

   106 						argument, or -1 if the argument is zero.

   107 	__e32_find_ls1_32	Return bit position of least significant 1 in a 32 bit

   108 						argument, or -1 if the argument is zero.

   109 	__e32_bit_count_32	Return the count of bits set to 1 in a 32 bit argument.

   110 	__e32_find_ms1_64	Return bit position of most significant 1 in a 64 bit

   111 						argument, or -1 if the argument is zero.

   112 	__e32_find_ls1_64	Return bit position of least significant 1 in a 64 bit

   113 						argument, or -1 if the argument is zero.

   114 	__e32_bit_count_64	Return the count of bits set to 1 in a 64 bit argument.

   115