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) */ 62