1 /* 2 * Memory barrier definitions. This is based on information published 3 * in the Processor Abstraction Layer and the System Abstraction Layer 4 * manual. 5 * 6 * Copyright (C) 1998-2003 Hewlett-Packard Co 7 * David Mosberger-Tang <davidm@hpl.hp.com> 8 * Copyright (C) 1999 Asit Mallick <asit.k.mallick@intel.com> 9 * Copyright (C) 1999 Don Dugger <don.dugger@intel.com> 10 */ 11 #ifndef _ASM_IA64_BARRIER_H 12 #define _ASM_IA64_BARRIER_H 13 14 #include <linux/compiler.h> 15 16 /* 17 * Macros to force memory ordering. In these descriptions, "previous" 18 * and "subsequent" refer to program order; "visible" means that all 19 * architecturally visible effects of a memory access have occurred 20 * (at a minimum, this means the memory has been read or written). 21 * 22 * wmb(): Guarantees that all preceding stores to memory- 23 * like regions are visible before any subsequent 24 * stores and that all following stores will be 25 * visible only after all previous stores. 26 * rmb(): Like wmb(), but for reads. 27 * mb(): wmb()/rmb() combo, i.e., all previous memory 28 * accesses are visible before all subsequent 29 * accesses and vice versa. This is also known as 30 * a "fence." 31 * 32 * Note: "mb()" and its variants cannot be used as a fence to order 33 * accesses to memory mapped I/O registers. For that, mf.a needs to 34 * be used. However, we don't want to always use mf.a because (a) 35 * it's (presumably) much slower than mf and (b) mf.a is supported for 36 * sequential memory pages only. 37 */ 38 #define mb() ia64_mf() 39 #define rmb() mb() 40 #define wmb() mb() 41 #define read_barrier_depends() do { } while(0) 42 43 #ifdef CONFIG_SMP 44 # define smp_mb() mb() 45 # define smp_rmb() rmb() 46 # define smp_wmb() wmb() 47 # define smp_read_barrier_depends() read_barrier_depends() 48 49 #else 50 51 # define smp_mb() barrier() 52 # define smp_rmb() barrier() 53 # define smp_wmb() barrier() 54 # define smp_read_barrier_depends() do { } while(0) 55 56 #endif 57 58 #define smp_mb__before_atomic() barrier() 59 #define smp_mb__after_atomic() barrier() 60 61 /* 62 * IA64 GCC turns volatile stores into st.rel and volatile loads into ld.acq no 63 * need for asm trickery! 64 */ 65 66 #define smp_store_release(p, v) \ 67 do { \ 68 compiletime_assert_atomic_type(*p); \ 69 barrier(); \ 70 ACCESS_ONCE(*p) = (v); \ 71 } while (0) 72 73 #define smp_load_acquire(p) \ 74 ({ \ 75 typeof(*p) ___p1 = ACCESS_ONCE(*p); \ 76 compiletime_assert_atomic_type(*p); \ 77 barrier(); \ 78 ___p1; \ 79 }) 80 81 /* 82 * XXX check on this ---I suspect what Linus really wants here is 83 * acquire vs release semantics but we can't discuss this stuff with 84 * Linus just yet. Grrr... 85 */ 86 #define set_mb(var, value) do { (var) = (value); mb(); } while (0) 87 88 /* 89 * The group barrier in front of the rsm & ssm are necessary to ensure 90 * that none of the previous instructions in the same group are 91 * affected by the rsm/ssm. 92 */ 93 94 #endif /* _ASM_IA64_BARRIER_H */ 95