1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __SPARC64_BARRIER_H
3 #define __SPARC64_BARRIER_H
4
5 /* These are here in an effort to more fully work around Spitfire Errata
6 * #51. Essentially, if a memory barrier occurs soon after a mispredicted
7 * branch, the chip can stop executing instructions until a trap occurs.
8 * Therefore, if interrupts are disabled, the chip can hang forever.
9 *
10 * It used to be believed that the memory barrier had to be right in the
11 * delay slot, but a case has been traced recently wherein the memory barrier
12 * was one instruction after the branch delay slot and the chip still hung.
13 * The offending sequence was the following in sym_wakeup_done() of the
14 * sym53c8xx_2 driver:
15 *
16 * call sym_ccb_from_dsa, 0
17 * movge %icc, 0, %l0
18 * brz,pn %o0, .LL1303
19 * mov %o0, %l2
20 * membar #LoadLoad
21 *
22 * The branch has to be mispredicted for the bug to occur. Therefore, we put
23 * the memory barrier explicitly into a "branch always, predicted taken"
24 * delay slot to avoid the problem case.
25 */
26 #define membar_safe(type) \
27 do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \
28 " membar " type "\n" \
29 "1:\n" \
30 : : : "memory"); \
31 } while (0)
32
33 /* The kernel always executes in TSO memory model these days,
34 * and furthermore most sparc64 chips implement more stringent
35 * memory ordering than required by the specifications.
36 */
37 #define mb() membar_safe("#StoreLoad")
38 #define rmb() __asm__ __volatile__("":::"memory")
39 #define wmb() __asm__ __volatile__("":::"memory")
40
41 #define __smp_store_release(p, v) \
42 do { \
43 compiletime_assert_atomic_type(*p); \
44 barrier(); \
45 WRITE_ONCE(*p, v); \
46 } while (0)
47
48 #define __smp_load_acquire(p) \
49 ({ \
50 typeof(*p) ___p1 = READ_ONCE(*p); \
51 compiletime_assert_atomic_type(*p); \
52 barrier(); \
53 ___p1; \
54 })
55
56 #define __smp_mb__before_atomic() barrier()
57 #define __smp_mb__after_atomic() barrier()
58
59 #include <asm-generic/barrier.h>
60
61 #endif /* !(__SPARC64_BARRIER_H) */