Merge branch 'upstream' of git://ftp.linux-mips.org/pub/scm/upstream-linus
[linux-2.6] / include / linux / bit_spinlock.h
1 #ifndef __LINUX_BIT_SPINLOCK_H
2 #define __LINUX_BIT_SPINLOCK_H
3
4 /*
5  *  bit-based spin_lock()
6  *
7  * Don't use this unless you really need to: spin_lock() and spin_unlock()
8  * are significantly faster.
9  */
10 static inline void bit_spin_lock(int bitnum, unsigned long *addr)
11 {
12         /*
13          * Assuming the lock is uncontended, this never enters
14          * the body of the outer loop. If it is contended, then
15          * within the inner loop a non-atomic test is used to
16          * busywait with less bus contention for a good time to
17          * attempt to acquire the lock bit.
18          */
19         preempt_disable();
20 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
21         while (test_and_set_bit(bitnum, addr)) {
22                 while (test_bit(bitnum, addr)) {
23                         preempt_enable();
24                         cpu_relax();
25                         preempt_disable();
26                 }
27         }
28 #endif
29         __acquire(bitlock);
30 }
31
32 /*
33  * Return true if it was acquired
34  */
35 static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
36 {
37         preempt_disable();
38 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
39         if (test_and_set_bit(bitnum, addr)) {
40                 preempt_enable();
41                 return 0;
42         }
43 #endif
44         __acquire(bitlock);
45         return 1;
46 }
47
48 /*
49  *  bit-based spin_unlock()
50  */
51 static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
52 {
53 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
54         BUG_ON(!test_bit(bitnum, addr));
55         smp_mb__before_clear_bit();
56         clear_bit(bitnum, addr);
57 #endif
58         preempt_enable();
59         __release(bitlock);
60 }
61
62 /*
63  * Return true if the lock is held.
64  */
65 static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
66 {
67 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
68         return test_bit(bitnum, addr);
69 #elif defined CONFIG_PREEMPT
70         return preempt_count();
71 #else
72         return 1;
73 #endif
74 }
75
76 #endif /* __LINUX_BIT_SPINLOCK_H */
77