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 #endif /* !(__TOOLS_LINUX_SPARC64_BARRIER_H) */
44