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/* $Id: dec_and_lock.S,v 1.1.1.1 2004-04-15 01:33:42 phoenix 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)
 */
#include <linux/config.h>

#ifndef CONFIG_DEBUG_SPINLOCK
        .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:
        membar  #StoreLoad | #StoreStore
        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) */
        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

#endif /* !(CONFIG_DEBUG_SPINLOCK) */