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/* $Id: dec_and_lock.S,v 1.2 2000/08/13 18:24:12 davem Exp $
* dec_and_lock.S: Sparc64 version of "atomic_dec_and_lock()"
* using cas and ldstub instructions.
*
* Copyright (C) 2000 David S. Miller (davem@redhat.com)
*/
.text
.align 64
/* CAS basically works like this:
*
* void CAS(MEM, REG1, REG2)
* {
* START_ATOMIC();
* if (*(MEM) == REG1) {
* TMP = *(MEM);
* *(MEM) = REG2;
* REG2 = TMP;
* } else
* REG2 = *(MEM);
* END_ATOMIC();
* }
*/
.globl atomic_dec_and_lock
atomic_dec_and_lock: /* %o0 = counter, %o1 = lock */
loop1: lduw [%o0], %g5
subcc %g5, 1, %g7
be,pn %icc, to_zero
nop
nzero: cas [%o0], %g5, %g7
cmp %g5, %g7
bne,pn %icc, loop1
mov 0, %g1
out: retl
mov %g1, %o0
to_zero:ldstub [%o1], %g3
brnz,pn %g3, spin_on_lock
membar #StoreLoad | #StoreStore
loop2: cas [%o0], %g5, %g7 /* ASSERT(g7 == 0) */
nop
cmp %g5, %g7
be,pt %icc, out
mov 1, %g1
lduw [%o0], %g5
subcc %g5, 1, %g7
be,pn %icc, loop2
nop
membar #StoreStore | #LoadStore
stb %g0, [%o1]
b,pt %xcc, nzero
nop
spin_on_lock:
ldub [%o1], %g3
brnz,pt %g3, spin_on_lock
membar #LoadLoad
ba,pt %xcc, to_zero
nop
nop
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