149618364SMauro Carvalho Chehab============= 249618364SMauro Carvalho ChehabAtomic bitops 349618364SMauro Carvalho Chehab============= 4706eeb3eSPeter Zijlstra 5706eeb3eSPeter ZijlstraWhile our bitmap_{}() functions are non-atomic, we have a number of operations 6706eeb3eSPeter Zijlstraoperating on single bits in a bitmap that are atomic. 7706eeb3eSPeter Zijlstra 8706eeb3eSPeter Zijlstra 9706eeb3eSPeter ZijlstraAPI 10706eeb3eSPeter Zijlstra--- 11706eeb3eSPeter Zijlstra 12706eeb3eSPeter ZijlstraThe single bit operations are: 13706eeb3eSPeter Zijlstra 14706eeb3eSPeter ZijlstraNon-RMW ops: 15706eeb3eSPeter Zijlstra 16706eeb3eSPeter Zijlstra test_bit() 17706eeb3eSPeter Zijlstra 18706eeb3eSPeter ZijlstraRMW atomic operations without return value: 19706eeb3eSPeter Zijlstra 20706eeb3eSPeter Zijlstra {set,clear,change}_bit() 21706eeb3eSPeter Zijlstra clear_bit_unlock() 22706eeb3eSPeter Zijlstra 23706eeb3eSPeter ZijlstraRMW atomic operations with return value: 24706eeb3eSPeter Zijlstra 25706eeb3eSPeter Zijlstra test_and_{set,clear,change}_bit() 26706eeb3eSPeter Zijlstra test_and_set_bit_lock() 27706eeb3eSPeter Zijlstra 28706eeb3eSPeter ZijlstraBarriers: 29706eeb3eSPeter Zijlstra 30706eeb3eSPeter Zijlstra smp_mb__{before,after}_atomic() 31706eeb3eSPeter Zijlstra 32706eeb3eSPeter Zijlstra 33706eeb3eSPeter ZijlstraAll RMW atomic operations have a '__' prefixed variant which is non-atomic. 34706eeb3eSPeter Zijlstra 35706eeb3eSPeter Zijlstra 36706eeb3eSPeter ZijlstraSEMANTICS 37706eeb3eSPeter Zijlstra--------- 38706eeb3eSPeter Zijlstra 39706eeb3eSPeter ZijlstraNon-atomic ops: 40706eeb3eSPeter Zijlstra 41706eeb3eSPeter ZijlstraIn particular __clear_bit_unlock() suffers the same issue as atomic_set(), 42706eeb3eSPeter Zijlstrawhich is why the generic version maps to clear_bit_unlock(), see atomic_t.txt. 43706eeb3eSPeter Zijlstra 44706eeb3eSPeter Zijlstra 45706eeb3eSPeter ZijlstraRMW ops: 46706eeb3eSPeter Zijlstra 47706eeb3eSPeter ZijlstraThe test_and_{}_bit() operations return the original value of the bit. 48706eeb3eSPeter Zijlstra 49706eeb3eSPeter Zijlstra 50706eeb3eSPeter ZijlstraORDERING 51706eeb3eSPeter Zijlstra-------- 52706eeb3eSPeter Zijlstra 53706eeb3eSPeter ZijlstraLike with atomic_t, the rule of thumb is: 54706eeb3eSPeter Zijlstra 55706eeb3eSPeter Zijlstra - non-RMW operations are unordered; 56706eeb3eSPeter Zijlstra 57706eeb3eSPeter Zijlstra - RMW operations that have no return value are unordered; 58706eeb3eSPeter Zijlstra 59706eeb3eSPeter Zijlstra - RMW operations that have a return value are fully ordered. 60706eeb3eSPeter Zijlstra 61*8238b457SMikulas Patocka - RMW operations that are conditional are fully ordered. 6261e02392SWill Deacon 63*8238b457SMikulas PatockaExcept for a successful test_and_set_bit_lock() which has ACQUIRE semantics, 64*8238b457SMikulas Patockaclear_bit_unlock() which has RELEASE semantics and test_bit_acquire which has 65*8238b457SMikulas PatockaACQUIRE semantics. 66706eeb3eSPeter Zijlstra 67706eeb3eSPeter ZijlstraSince a platform only has a single means of achieving atomic operations 68706eeb3eSPeter Zijlstrathe same barriers as for atomic_t are used, see atomic_t.txt. 69706eeb3eSPeter Zijlstra 70