tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1/*
2 * Copyright 2011 Tilera Corporation. All Rights Reserved.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation, version 2.
7 *
8 * This program is distributed in the hope that it will be useful, but
9 * WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
11 * NON INFRINGEMENT. See the GNU General Public License for
12 * more details.
13 */
14
15#include <linux/spinlock.h>
16#include <linux/module.h>
17#include <asm/processor.h>
18
19#include "spinlock_common.h"
20
21/*
22 * Read the spinlock value without allocating in our cache and without
23 * causing an invalidation to another cpu with a copy of the cacheline.
24 * This is important when we are spinning waiting for the lock.
25 */
26static inline u32 arch_spin_read_noalloc(void *lock)
27{
28 return atomic_cmpxchg((atomic_t *)lock, -1, -1);
29}
30
31/*
32 * Wait until the high bits (current) match my ticket.
33 * If we notice the overflow bit set on entry, we clear it.
34 */
35void arch_spin_lock_slow(arch_spinlock_t *lock, u32 my_ticket)
36{
37 if (unlikely(my_ticket & __ARCH_SPIN_NEXT_OVERFLOW)) {
38 __insn_fetchand4(&lock->lock, ~__ARCH_SPIN_NEXT_OVERFLOW);
39 my_ticket &= ~__ARCH_SPIN_NEXT_OVERFLOW;
40 }
41
42 for (;;) {
43 u32 val = arch_spin_read_noalloc(lock);
44 u32 delta = my_ticket - arch_spin_current(val);
45 if (delta == 0)
46 return;
47 relax((128 / CYCLES_PER_RELAX_LOOP) * delta);
48 }
49}
50EXPORT_SYMBOL(arch_spin_lock_slow);
51
52/*
53 * Check the lock to see if it is plausible, and try to get it with cmpxchg().
54 */
55int arch_spin_trylock(arch_spinlock_t *lock)
56{
57 u32 val = arch_spin_read_noalloc(lock);
58 if (unlikely(arch_spin_current(val) != arch_spin_next(val)))
59 return 0;
60 return cmpxchg(&lock->lock, val, (val + 1) & ~__ARCH_SPIN_NEXT_OVERFLOW)
61 == val;
62}
63EXPORT_SYMBOL(arch_spin_trylock);
64
65void arch_spin_unlock_wait(arch_spinlock_t *lock)
66{
67 u32 iterations = 0;
68 u32 val = READ_ONCE(lock->lock);
69 u32 curr = arch_spin_current(val);
70
71 /* Return immediately if unlocked. */
72 if (arch_spin_next(val) == curr)
73 return;
74
75 /* Wait until the current locker has released the lock. */
76 do {
77 delay_backoff(iterations++);
78 } while (arch_spin_current(READ_ONCE(lock->lock)) == curr);
79
80 /*
81 * The TILE architecture doesn't do read speculation; therefore
82 * a control dependency guarantees a LOAD->{LOAD,STORE} order.
83 */
84 barrier();
85}
86EXPORT_SYMBOL(arch_spin_unlock_wait);
87
88/*
89 * If the read lock fails due to a writer, we retry periodically
90 * until the value is positive and we write our incremented reader count.
91 */
92void __read_lock_failed(arch_rwlock_t *rw)
93{
94 u32 val;
95 int iterations = 0;
96 do {
97 delay_backoff(iterations++);
98 val = __insn_fetchaddgez4(&rw->lock, 1);
99 } while (unlikely(arch_write_val_locked(val)));
100}
101EXPORT_SYMBOL(__read_lock_failed);
102
103/*
104 * If we failed because there were readers, clear the "writer" bit
105 * so we don't block additional readers. Otherwise, there was another
106 * writer anyway, so our "fetchor" made no difference. Then wait,
107 * issuing periodic fetchor instructions, till we get the lock.
108 */
109void __write_lock_failed(arch_rwlock_t *rw, u32 val)
110{
111 int iterations = 0;
112 do {
113 if (!arch_write_val_locked(val))
114 val = __insn_fetchand4(&rw->lock, ~__WRITE_LOCK_BIT);
115 delay_backoff(iterations++);
116 val = __insn_fetchor4(&rw->lock, __WRITE_LOCK_BIT);
117 } while (val != 0);
118}
119EXPORT_SYMBOL(__write_lock_failed);