1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* Atomic operations usable in machine independent code */ 3 #ifndef _LINUX_ATOMIC_H 4 #define _LINUX_ATOMIC_H 5 #include <linux/types.h> 6 7 #include <asm/atomic.h> 8 #include <asm/barrier.h> 9 10 /* 11 * Relaxed variants of xchg, cmpxchg and some atomic operations. 12 * 13 * We support four variants: 14 * 15 * - Fully ordered: The default implementation, no suffix required. 16 * - Acquire: Provides ACQUIRE semantics, _acquire suffix. 17 * - Release: Provides RELEASE semantics, _release suffix. 18 * - Relaxed: No ordering guarantees, _relaxed suffix. 19 * 20 * For compound atomics performing both a load and a store, ACQUIRE 21 * semantics apply only to the load and RELEASE semantics only to the 22 * store portion of the operation. Note that a failed cmpxchg_acquire 23 * does -not- imply any memory ordering constraints. 24 * 25 * See Documentation/memory-barriers.txt for ACQUIRE/RELEASE definitions. 26 */ 27 28 /* 29 * The idea here is to build acquire/release variants by adding explicit 30 * barriers on top of the relaxed variant. In the case where the relaxed 31 * variant is already fully ordered, no additional barriers are needed. 32 * 33 * If an architecture overrides __atomic_acquire_fence() it will probably 34 * want to define smp_mb__after_spinlock(). 35 */ 36 #ifndef __atomic_acquire_fence 37 #define __atomic_acquire_fence smp_mb__after_atomic 38 #endif 39 40 #ifndef __atomic_release_fence 41 #define __atomic_release_fence smp_mb__before_atomic 42 #endif 43 44 #ifndef __atomic_pre_full_fence 45 #define __atomic_pre_full_fence smp_mb__before_atomic 46 #endif 47 48 #ifndef __atomic_post_full_fence 49 #define __atomic_post_full_fence smp_mb__after_atomic 50 #endif 51 52 #define __atomic_op_acquire(op, args...) \ 53 ({ \ 54 typeof(op##_relaxed(args)) __ret = op##_relaxed(args); \ 55 __atomic_acquire_fence(); \ 56 __ret; \ 57 }) 58 59 #define __atomic_op_release(op, args...) \ 60 ({ \ 61 __atomic_release_fence(); \ 62 op##_relaxed(args); \ 63 }) 64 65 #define __atomic_op_fence(op, args...) \ 66 ({ \ 67 typeof(op##_relaxed(args)) __ret; \ 68 __atomic_pre_full_fence(); \ 69 __ret = op##_relaxed(args); \ 70 __atomic_post_full_fence(); \ 71 __ret; \ 72 }) 73 74 #include <linux/atomic-fallback.h> 75 76 #include <asm-generic/atomic-long.h> 77 78 #endif /* _LINUX_ATOMIC_H */ 79