| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /* $Id: dec_and_lock.S,v 1.5 2001/11/18 00:12:56 davem Exp $ |
| 2 | * dec_and_lock.S: Sparc64 version of "atomic_dec_and_lock()" |
| 3 | * using cas and ldstub instructions. |
| 4 | * |
| 5 | * Copyright (C) 2000 David S. Miller (davem@redhat.com) |
| 6 | */ |
| 7 | #include <linux/config.h> |
| 8 | #include <asm/thread_info.h> |
| 9 | |
| 10 | .text |
| 11 | .align 64 |
| 12 | |
| 13 | /* CAS basically works like this: |
| 14 | * |
| 15 | * void CAS(MEM, REG1, REG2) |
| 16 | * { |
| 17 | * START_ATOMIC(); |
| 18 | * if (*(MEM) == REG1) { |
| 19 | * TMP = *(MEM); |
| 20 | * *(MEM) = REG2; |
| 21 | * REG2 = TMP; |
| 22 | * } else |
| 23 | * REG2 = *(MEM); |
| 24 | * END_ATOMIC(); |
| 25 | * } |
| 26 | */ |
| 27 | |
| 28 | .globl _atomic_dec_and_lock |
| 29 | _atomic_dec_and_lock: /* %o0 = counter, %o1 = lock */ |
| 30 | loop1: lduw [%o0], %g2 |
| 31 | subcc %g2, 1, %g7 |
| 32 | be,pn %icc, start_to_zero |
| 33 | nop |
| 34 | nzero: cas [%o0], %g2, %g7 |
| 35 | cmp %g2, %g7 |
| 36 | bne,pn %icc, loop1 |
| 37 | mov 0, %g1 |
| 38 | |
| 39 | out: |
| 40 | membar #StoreLoad | #StoreStore |
| 41 | retl |
| 42 | mov %g1, %o0 |
| 43 | start_to_zero: |
| 44 | #ifdef CONFIG_PREEMPT |
| 45 | ldsw [%g6 + TI_PRE_COUNT], %g3 |
| 46 | add %g3, 1, %g3 |
| 47 | stw %g3, [%g6 + TI_PRE_COUNT] |
| 48 | #endif |
| 49 | to_zero: |
| 50 | ldstub [%o1], %g3 |
| 51 | brnz,pn %g3, spin_on_lock |
| 52 | membar #StoreLoad | #StoreStore |
| 53 | loop2: cas [%o0], %g2, %g7 /* ASSERT(g7 == 0) */ |
| 54 | cmp %g2, %g7 |
| 55 | |
| 56 | be,pt %icc, out |
| 57 | mov 1, %g1 |
| 58 | lduw [%o0], %g2 |
| 59 | subcc %g2, 1, %g7 |
| 60 | be,pn %icc, loop2 |
| 61 | nop |
| 62 | membar #StoreStore | #LoadStore |
| 63 | stb %g0, [%o1] |
| 64 | #ifdef CONFIG_PREEMPT |
| 65 | ldsw [%g6 + TI_PRE_COUNT], %g3 |
| 66 | sub %g3, 1, %g3 |
| 67 | stw %g3, [%g6 + TI_PRE_COUNT] |
| 68 | #endif |
| 69 | |
| 70 | b,pt %xcc, nzero |
| 71 | nop |
| 72 | spin_on_lock: |
| 73 | ldub [%o1], %g3 |
| 74 | brnz,pt %g3, spin_on_lock |
| 75 | membar #LoadLoad |
| 76 | ba,pt %xcc, to_zero |
| 77 | nop |
| 78 | nop |