1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __ASM_SPINLOCK_H
3 #define __ASM_SPINLOCK_H
4
5 #include <asm/barrier.h>
6 #include <asm/ldcw.h>
7 #include <asm/processor.h>
8 #include <asm/spinlock_types.h>
9
10 static inline void arch_spin_val_check(int lock_val)
11 {
12 if (IS_ENABLED(CONFIG_LIGHTWEIGHT_SPINLOCK_CHECK))
13 asm volatile( "andcm,= %0,%1,%%r0\n"
14 ".word %2\n"
15 : : "r" (lock_val), "r" (__ARCH_SPIN_LOCK_UNLOCKED_VAL),
16 "i" (SPINLOCK_BREAK_INSN));
17 }
18
19 static inline int arch_spin_is_locked(arch_spinlock_t *x)
20 {
21 volatile unsigned int *a;
22 int lock_val;
23
24 a = __ldcw_align(x);
25 lock_val = READ_ONCE(*a);
26 arch_spin_val_check(lock_val);
27 return (lock_val == 0);
28 }
29
30 static inline void arch_spin_lock(arch_spinlock_t *x)
31 {
32 volatile unsigned int *a;
33
34 a = __ldcw_align(x);
35 do {
36 int lock_val_old;
37
38 lock_val_old = __ldcw(a);
39 arch_spin_val_check(lock_val_old);
40 if (lock_val_old)
41 return; /* got lock */
42
43 /* wait until we should try to get lock again */
44 while (*a == 0)
45 continue;
46 } while (1);
47 }
48
49 static inline void arch_spin_unlock(arch_spinlock_t *x)
50 {
51 volatile unsigned int *a;
52
53 a = __ldcw_align(x);
54 /* Release with ordered store. */
55 __asm__ __volatile__("stw,ma %0,0(%1)"
56 : : "r"(__ARCH_SPIN_LOCK_UNLOCKED_VAL), "r"(a) : "memory");
57 }
58
59 static inline int arch_spin_trylock(arch_spinlock_t *x)
60 {
61 volatile unsigned int *a;
62 int lock_val;
63
64 a = __ldcw_align(x);
65 lock_val = __ldcw(a);
66 arch_spin_val_check(lock_val);
67 return lock_val != 0;
68 }
69
70 /*
71 * Read-write spinlocks, allowing multiple readers but only one writer.
72 * Unfair locking as Writers could be starved indefinitely by Reader(s)
73 *
74 * The spinlock itself is contained in @counter and access to it is
75 * serialized with @lock_mutex.
76 */
77
78 /* 1 - lock taken successfully */
79 static inline int arch_read_trylock(arch_rwlock_t *rw)
80 {
81 int ret = 0;
82 unsigned long flags;
83
84 local_irq_save(flags);
85 arch_spin_lock(&(rw->lock_mutex));
86
87 /*
88 * zero means writer holds the lock exclusively, deny Reader.
89 * Otherwise grant lock to first/subseq reader
90 */
91 if (rw->counter > 0) {
92 rw->counter--;
93 ret = 1;
94 }
95
96 arch_spin_unlock(&(rw->lock_mutex));
97 local_irq_restore(flags);
98
99 return ret;
100 }
101
102 /* 1 - lock taken successfully */
103 static inline int arch_write_trylock(arch_rwlock_t *rw)
104 {
105 int ret = 0;
106 unsigned long flags;
107
108 local_irq_save(flags);
109 arch_spin_lock(&(rw->lock_mutex));
110
111 /*
112 * If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
113 * deny writer. Otherwise if unlocked grant to writer
114 * Hence the claim that Linux rwlocks are unfair to writers.
115 * (can be starved for an indefinite time by readers).
116 */
117 if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
118 rw->counter = 0;
119 ret = 1;
120 }
121 arch_spin_unlock(&(rw->lock_mutex));
122 local_irq_restore(flags);
123
124 return ret;
125 }
126
127 static inline void arch_read_lock(arch_rwlock_t *rw)
128 {
129 while (!arch_read_trylock(rw))
130 cpu_relax();
131 }
132
133 static inline void arch_write_lock(arch_rwlock_t *rw)
134 {
135 while (!arch_write_trylock(rw))
136 cpu_relax();
137 }
138
139 static inline void arch_read_unlock(arch_rwlock_t *rw)
140 {
141 unsigned long flags;
142
143 local_irq_save(flags);
144 arch_spin_lock(&(rw->lock_mutex));
145 rw->counter++;
146 arch_spin_unlock(&(rw->lock_mutex));
147 local_irq_restore(flags);
148 }
149
150 static inline void arch_write_unlock(arch_rwlock_t *rw)
151 {
152 unsigned long flags;
153
154 local_irq_save(flags);
155 arch_spin_lock(&(rw->lock_mutex));
156 rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
157 arch_spin_unlock(&(rw->lock_mutex));
158 local_irq_restore(flags);
159 }
160
161 #endif /* __ASM_SPINLOCK_H */
162
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