1/*
2 * Copyright (C) 2018, Emilio G. Cota <cota@braap.org>
3 *
4 * License: GNU GPL, version 2 or later.
5 * See the COPYING file in the top-level directory.
6 */
7#include "qemu/osdep.h"
8#include "qemu/atomic.h"
9#include "qemu/thread.h"
10
11#ifdef CONFIG_ATOMIC64
12#error This file must only be compiled if !CONFIG_ATOMIC64
13#endif
14
15/*
16 * When !CONFIG_ATOMIC64, we serialize both reads and writes with spinlocks.
17 * We use an array of spinlocks, with padding computed at run-time based on
18 * the host's dcache line size.
19 * We point to the array with a void * to simplify the padding's computation.
20 * Each spinlock is located every lock_size bytes.
21 */
22static void *lock_array;
23static size_t lock_size;
24
25/*
26 * Systems without CONFIG_ATOMIC64 are unlikely to have many cores, so we use a
27 * small array of locks.
28 */
29#define NR_LOCKS 16
30
31static QemuSpin *addr_to_lock(const void *addr)
32{
33 uintptr_t a = (uintptr_t)addr;
34 uintptr_t idx;
35
36 idx = a >> qemu_dcache_linesize_log;
37 idx ^= (idx >> 8) ^ (idx >> 16);
38 idx &= NR_LOCKS - 1;
39 return lock_array + idx * lock_size;
40}
41
42#define GEN_READ(name, type) \
43 type name(const type *ptr) \
44 { \
45 QemuSpin *lock = addr_to_lock(ptr); \
46 type ret; \
47 \
48 qemu_spin_lock(lock); \
49 ret = *ptr; \
50 qemu_spin_unlock(lock); \
51 return ret; \
52 }
53
54GEN_READ(atomic_read_i64, int64_t)
55GEN_READ(atomic_read_u64, uint64_t)
56#undef GEN_READ
57
58#define GEN_SET(name, type) \
59 void name(type *ptr, type val) \
60 { \
61 QemuSpin *lock = addr_to_lock(ptr); \
62 \
63 qemu_spin_lock(lock); \
64 *ptr = val; \
65 qemu_spin_unlock(lock); \
66 }
67
68GEN_SET(atomic_set_i64, int64_t)
69GEN_SET(atomic_set_u64, uint64_t)
70#undef GEN_SET
71
72void atomic64_init(void)
73{
74 int i;
75
76 lock_size = ROUND_UP(sizeof(QemuSpin), qemu_dcache_linesize);
77 lock_array = qemu_memalign(qemu_dcache_linesize, lock_size * NR_LOCKS);
78 for (i = 0; i < NR_LOCKS; i++) {
79 QemuSpin *lock = lock_array + i * lock_size;
80
81 qemu_spin_init(lock);
82 }
83}
84