include/asm/sync.h

1 /* SPDX-License-Identifier: GPL-2.0-only */
6  * sync types are defined by the MIPS64 Instruction Set documentation in Volume
7  * II-A of the MIPS Architecture Reference Manual, which can be found here:
9  *   https://www.mips.com/?do-download=the-mips64-instruction-set-v6-06
16  *   2) Ordering barriers, which only ensure that affected memory operations
27  *      actually need to complete - they just need to get far enough that all
43  * No sync instruction at all; used to allow code to nullify the effect of the
46 #define __SYNC_none	-1
49  * A full completion barrier; all memory accesses appearing prior to this sync
51  * appearing after this sync instruction in program order.
56  * For now we use a full completion barrier to implement all sync types, until
78  * A GINV sync is a little different; it doesn't relate directly to loads or
82  * has been performed by all coherent CPUs, we must issue a sync instruction of
88 /* Trivial; indicate that we always need this sync instruction. */
92  * Indicate that we need this sync instruction only on systems with weakly
103  * Indicate that we need this sync instruction only on systems where LL/SC
108 # define __SYNC_weak_llsc	(1 << 2)
121  *    be executed after the LL - this is the reordering case.
123  *    In order to avoid this we need to place a memory barrier (ie. a SYNC
129  * 2) If a conditional branch exists between an LL & SC with a target outside
130  *    of the LL-SC loop, for example an exit upon value mismatch in cmpxchg()
132  *    execution of memory accesses from outside of the LL-SC loop.
134  *    In order to avoid this we need a memory barrier (ie. a SYNC instruction)
140  * such that the Invalidate of a competing LL-SC goes 'missing' and SC
154  * barrier to be ineffective, requiring the use of 2 in sequence to provide an
157  * sync instructions should be emitted twice.
159  * and that the assembler evaluates '==' as 0 or -1, not 0 or 1.
162 # define __SYNC_rpt(type)	(1 - (type == __SYNC_wmb))
168  * The main event. Here we actually emit a sync instruction of a given type, if
169  * reason is non-zero.
171  * In future we have the option of emitting entries in a fixups-style table
172  * here that would allow us to opportunistically remove some sync instructions
178 	.if	(( _type ) != -1) && ( _reason );		\
182 	sync	_type;						\