xref: /openbmc/linux/include/linux/bit_spinlock.h (revision b2441318)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __LINUX_BIT_SPINLOCK_H
3 #define __LINUX_BIT_SPINLOCK_H
4 
5 #include <linux/kernel.h>
6 #include <linux/preempt.h>
7 #include <linux/atomic.h>
8 #include <linux/bug.h>
9 
10 /*
11  *  bit-based spin_lock()
12  *
13  * Don't use this unless you really need to: spin_lock() and spin_unlock()
14  * are significantly faster.
15  */
bit_spin_lock(int bitnum,unsigned long * addr)16 static inline void bit_spin_lock(int bitnum, unsigned long *addr)
17 {
18 	/*
19 	 * Assuming the lock is uncontended, this never enters
20 	 * the body of the outer loop. If it is contended, then
21 	 * within the inner loop a non-atomic test is used to
22 	 * busywait with less bus contention for a good time to
23 	 * attempt to acquire the lock bit.
24 	 */
25 	preempt_disable();
26 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
27 	while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
28 		preempt_enable();
29 		do {
30 			cpu_relax();
31 		} while (test_bit(bitnum, addr));
32 		preempt_disable();
33 	}
34 #endif
35 	__acquire(bitlock);
36 }
37 
38 /*
39  * Return true if it was acquired
40  */
bit_spin_trylock(int bitnum,unsigned long * addr)41 static inline int bit_spin_trylock(int bitnum, unsigned long *addr)
42 {
43 	preempt_disable();
44 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
45 	if (unlikely(test_and_set_bit_lock(bitnum, addr))) {
46 		preempt_enable();
47 		return 0;
48 	}
49 #endif
50 	__acquire(bitlock);
51 	return 1;
52 }
53 
54 /*
55  *  bit-based spin_unlock()
56  */
bit_spin_unlock(int bitnum,unsigned long * addr)57 static inline void bit_spin_unlock(int bitnum, unsigned long *addr)
58 {
59 #ifdef CONFIG_DEBUG_SPINLOCK
60 	BUG_ON(!test_bit(bitnum, addr));
61 #endif
62 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
63 	clear_bit_unlock(bitnum, addr);
64 #endif
65 	preempt_enable();
66 	__release(bitlock);
67 }
68 
69 /*
70  *  bit-based spin_unlock()
71  *  non-atomic version, which can be used eg. if the bit lock itself is
72  *  protecting the rest of the flags in the word.
73  */
__bit_spin_unlock(int bitnum,unsigned long * addr)74 static inline void __bit_spin_unlock(int bitnum, unsigned long *addr)
75 {
76 #ifdef CONFIG_DEBUG_SPINLOCK
77 	BUG_ON(!test_bit(bitnum, addr));
78 #endif
79 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
80 	__clear_bit_unlock(bitnum, addr);
81 #endif
82 	preempt_enable();
83 	__release(bitlock);
84 }
85 
86 /*
87  * Return true if the lock is held.
88  */
bit_spin_is_locked(int bitnum,unsigned long * addr)89 static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
90 {
91 #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
92 	return test_bit(bitnum, addr);
93 #elif defined CONFIG_PREEMPT_COUNT
94 	return preempt_count();
95 #else
96 	return 1;
97 #endif
98 }
99 
100 #endif /* __LINUX_BIT_SPINLOCK_H */
101 
102