1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __ASM_SPINLOCK_H
3 #define __ASM_SPINLOCK_H
4
5 #if __LINUX_ARM_ARCH__ < 6
6 #error SMP not supported on pre-ARMv6 CPUs
7 #endif
8
9 #include <linux/prefetch.h>
10 #include <asm/barrier.h>
11 #include <asm/processor.h>
12
13 /*
14 * sev and wfe are ARMv6K extensions. Uniprocessor ARMv6 may not have the K
15 * extensions, so when running on UP, we have to patch these instructions away.
16 */
17 #ifdef CONFIG_THUMB2_KERNEL
18 /*
19 * For Thumb-2, special care is needed to ensure that the conditional WFE
20 * instruction really does assemble to exactly 4 bytes (as required by
21 * the SMP_ON_UP fixup code). By itself "wfene" might cause the
22 * assembler to insert a extra (16-bit) IT instruction, depending on the
23 * presence or absence of neighbouring conditional instructions.
24 *
25 * To avoid this unpredictability, an appropriate IT is inserted explicitly:
26 * the assembler won't change IT instructions which are explicitly present
27 * in the input.
28 */
29 #define WFE(cond) __ALT_SMP_ASM( \
30 "it " cond "\n\t" \
31 "wfe" cond ".n", \
32 \
33 "nop.w" \
34 )
35 #else
36 #define WFE(cond) __ALT_SMP_ASM("wfe" cond, "nop")
37 #endif
38
39 #define SEV __ALT_SMP_ASM(WASM(sev), WASM(nop))
40
41 static inline void dsb_sev(void)
42 {
43
44 dsb(ishst);
45 __asm__(SEV);
46 }
47
48 /*
49 * ARMv6 ticket-based spin-locking.
50 *
51 * A memory barrier is required after we get a lock, and before we
52 * release it, because V6 CPUs are assumed to have weakly ordered
53 * memory.
54 */
55
56 static inline void arch_spin_lock(arch_spinlock_t *lock)
57 {
58 unsigned long tmp;
59 u32 newval;
60 arch_spinlock_t lockval;
61
62 prefetchw(&lock->slock);
63 __asm__ __volatile__(
64 "1: ldrex %0, [%3]\n"
65 " add %1, %0, %4\n"
66 " strex %2, %1, [%3]\n"
67 " teq %2, #0\n"
68 " bne 1b"
69 : "=&r" (lockval), "=&r" (newval), "=&r" (tmp)
70 : "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
71 : "cc");
72
73 while (lockval.tickets.next != lockval.tickets.owner) {
74 wfe();
75 lockval.tickets.owner = READ_ONCE(lock->tickets.owner);
76 }
77
78 smp_mb();
79 }
80
81 static inline int arch_spin_trylock(arch_spinlock_t *lock)
82 {
83 unsigned long contended, res;
84 u32 slock;
85
86 prefetchw(&lock->slock);
87 do {
88 __asm__ __volatile__(
89 " ldrex %0, [%3]\n"
90 " mov %2, #0\n"
91 " subs %1, %0, %0, ror #16\n"
92 " addeq %0, %0, %4\n"
93 " strexeq %2, %0, [%3]"
94 : "=&r" (slock), "=&r" (contended), "=&r" (res)
95 : "r" (&lock->slock), "I" (1 << TICKET_SHIFT)
96 : "cc");
97 } while (res);
98
99 if (!contended) {
100 smp_mb();
101 return 1;
102 } else {
103 return 0;
104 }
105 }
106
107 static inline void arch_spin_unlock(arch_spinlock_t *lock)
108 {
109 smp_mb();
110 lock->tickets.owner++;
111 dsb_sev();
112 }
113
114 static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
115 {
116 return lock.tickets.owner == lock.tickets.next;
117 }
118
119 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
120 {
121 return !arch_spin_value_unlocked(READ_ONCE(*lock));
122 }
123
124 static inline int arch_spin_is_contended(arch_spinlock_t *lock)
125 {
126 struct __raw_tickets tickets = READ_ONCE(lock->tickets);
127 return (tickets.next - tickets.owner) > 1;
128 }
129 #define arch_spin_is_contended arch_spin_is_contended
130
131 /*
132 * RWLOCKS
133 *
134 *
135 * Write locks are easy - we just set bit 31. When unlocking, we can
136 * just write zero since the lock is exclusively held.
137 */
138
139 static inline void arch_write_lock(arch_rwlock_t *rw)
140 {
141 unsigned long tmp;
142
143 prefetchw(&rw->lock);
144 __asm__ __volatile__(
145 "1: ldrex %0, [%1]\n"
146 " teq %0, #0\n"
147 WFE("ne")
148 " strexeq %0, %2, [%1]\n"
149 " teq %0, #0\n"
150 " bne 1b"
151 : "=&r" (tmp)
152 : "r" (&rw->lock), "r" (0x80000000)
153 : "cc");
154
155 smp_mb();
156 }
157
158 static inline int arch_write_trylock(arch_rwlock_t *rw)
159 {
160 unsigned long contended, res;
161
162 prefetchw(&rw->lock);
163 do {
164 __asm__ __volatile__(
165 " ldrex %0, [%2]\n"
166 " mov %1, #0\n"
167 " teq %0, #0\n"
168 " strexeq %1, %3, [%2]"
169 : "=&r" (contended), "=&r" (res)
170 : "r" (&rw->lock), "r" (0x80000000)
171 : "cc");
172 } while (res);
173
174 if (!contended) {
175 smp_mb();
176 return 1;
177 } else {
178 return 0;
179 }
180 }
181
182 static inline void arch_write_unlock(arch_rwlock_t *rw)
183 {
184 smp_mb();
185
186 __asm__ __volatile__(
187 "str %1, [%0]\n"
188 :
189 : "r" (&rw->lock), "r" (0)
190 : "cc");
191
192 dsb_sev();
193 }
194
195 /*
196 * Read locks are a bit more hairy:
197 * - Exclusively load the lock value.
198 * - Increment it.
199 * - Store new lock value if positive, and we still own this location.
200 * If the value is negative, we've already failed.
201 * - If we failed to store the value, we want a negative result.
202 * - If we failed, try again.
203 * Unlocking is similarly hairy. We may have multiple read locks
204 * currently active. However, we know we won't have any write
205 * locks.
206 */
207 static inline void arch_read_lock(arch_rwlock_t *rw)
208 {
209 unsigned long tmp, tmp2;
210
211 prefetchw(&rw->lock);
212 __asm__ __volatile__(
213 " .syntax unified\n"
214 "1: ldrex %0, [%2]\n"
215 " adds %0, %0, #1\n"
216 " strexpl %1, %0, [%2]\n"
217 WFE("mi")
218 " rsbspl %0, %1, #0\n"
219 " bmi 1b"
220 : "=&r" (tmp), "=&r" (tmp2)
221 : "r" (&rw->lock)
222 : "cc");
223
224 smp_mb();
225 }
226
227 static inline void arch_read_unlock(arch_rwlock_t *rw)
228 {
229 unsigned long tmp, tmp2;
230
231 smp_mb();
232
233 prefetchw(&rw->lock);
234 __asm__ __volatile__(
235 "1: ldrex %0, [%2]\n"
236 " sub %0, %0, #1\n"
237 " strex %1, %0, [%2]\n"
238 " teq %1, #0\n"
239 " bne 1b"
240 : "=&r" (tmp), "=&r" (tmp2)
241 : "r" (&rw->lock)
242 : "cc");
243
244 if (tmp == 0)
245 dsb_sev();
246 }
247
248 static inline int arch_read_trylock(arch_rwlock_t *rw)
249 {
250 unsigned long contended, res;
251
252 prefetchw(&rw->lock);
253 do {
254 __asm__ __volatile__(
255 " ldrex %0, [%2]\n"
256 " mov %1, #0\n"
257 " adds %0, %0, #1\n"
258 " strexpl %1, %0, [%2]"
259 : "=&r" (contended), "=&r" (res)
260 : "r" (&rw->lock)
261 : "cc");
262 } while (res);
263
264 /* If the lock is negative, then it is already held for write. */
265 if (contended < 0x80000000) {
266 smp_mb();
267 return 1;
268 } else {
269 return 0;
270 }
271 }
272
273 #endif /* __ASM_SPINLOCK_H */
274
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