1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __TOOLS_LINUX_SPARC64_BARRIER_H
3 #define __TOOLS_LINUX_SPARC64_BARRIER_H
4
5 /* Copied from the kernel sources to tools/:
6 *
7 * These are here in an effort to more fully work around Spitfire Errata
8 * #51. Essentially, if a memory barrier occurs soon after a mispredicted
9 * branch, the chip can stop executing instructions until a trap occurs.
10 * Therefore, if interrupts are disabled, the chip can hang forever.
11 *
12 * It used to be believed that the memory barrier had to be right in the
13 * delay slot, but a case has been traced recently wherein the memory barrier
14 * was one instruction after the branch delay slot and the chip still hung.
15 * The offending sequence was the following in sym_wakeup_done() of the
16 * sym53c8xx_2 driver:
17 *
18 * call sym_ccb_from_dsa, 0
19 * movge %icc, 0, %l0
20 * brz,pn %o0, .LL1303
21 * mov %o0, %l2
22 * membar #LoadLoad
23 *
24 * The branch has to be mispredicted for the bug to occur. Therefore, we put
25 * the memory barrier explicitly into a "branch always, predicted taken"
26 * delay slot to avoid the problem case.
27 */
28 #define membar_safe(type) \
29 do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \
30 " membar " type "\n" \
31 "1:\n" \
32 : : : "memory"); \
33 } while (0)
34
35 /* The kernel always executes in TSO memory model these days,
36 * and furthermore most sparc64 chips implement more stringent
37 * memory ordering than required by the specifications.
38 */
39 #define mb() membar_safe("#StoreLoad")
40 #define rmb() __asm__ __volatile__("":::"memory")
41 #define wmb() __asm__ __volatile__("":::"memory")
42
43 #define smp_store_release(p, v) \
44 do { \
45 barrier(); \
46 WRITE_ONCE(*p, v); \
47 } while (0)
48
49 #define smp_load_acquire(p) \
50 ({ \
51 typeof(*p) ___p1 = READ_ONCE(*p); \
52 barrier(); \
53 ___p1; \
54 })
55
56 #endif /* !(__TOOLS_LINUX_SPARC64_BARRIER_H) */
57
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