| David S. Miller | 4f07118 | 2005-08-29 12:46:22 -0700 | [diff] [blame] | 1 | /* mb.S: Out of line memory barriers. |
| 2 | * |
| 3 | * Copyright (C) 2005 David S. Miller (davem@davemloft.net) |
| 4 | */ |
| 5 | |
| 6 | /* These are here in an effort to more fully work around |
| 7 | * Spitfire Errata #51. Essentially, if a memory barrier |
| 8 | * occurs soon after a mispredicted branch, the chip can stop |
| 9 | * executing instructions until a trap occurs. Therefore, if |
| 10 | * interrupts are disabled, the chip can hang forever. |
| 11 | * |
| 12 | * It used to be believed that the memory barrier had to be |
| 13 | * right in the delay slot, but a case has been traced |
| 14 | * recently wherein the memory barrier was one instruction |
| 15 | * after the branch delay slot and the chip still hung. The |
| 16 | * offending sequence was the following in sym_wakeup_done() |
| 17 | * of the sym53c8xx_2 driver: |
| 18 | * |
| 19 | * call sym_ccb_from_dsa, 0 |
| 20 | * movge %icc, 0, %l0 |
| 21 | * brz,pn %o0, .LL1303 |
| 22 | * mov %o0, %l2 |
| 23 | * membar #LoadLoad |
| 24 | * |
| 25 | * The branch has to be mispredicted for the bug to occur. |
| 26 | * Therefore, we put the memory barrier explicitly into a |
| 27 | * "branch always, predicted taken" delay slot to avoid the |
| 28 | * problem case. |
| 29 | */ |
| 30 | |
| 31 | .text |
| 32 | |
| 33 | 99: retl |
| 34 | nop |
| 35 | |
| 36 | .globl mb |
| 37 | mb: ba,pt %xcc, 99b |
| 38 | membar #LoadLoad | #LoadStore | #StoreStore | #StoreLoad |
| 39 | .size mb, .-mb |
| 40 | |
| 41 | .globl rmb |
| 42 | rmb: ba,pt %xcc, 99b |
| 43 | membar #LoadLoad |
| 44 | .size rmb, .-rmb |
| 45 | |
| 46 | .globl wmb |
| 47 | wmb: ba,pt %xcc, 99b |
| 48 | membar #StoreStore |
| 49 | .size wmb, .-wmb |
| 50 | |
| 51 | .globl membar_storeload |
| 52 | membar_storeload: |
| 53 | ba,pt %xcc, 99b |
| 54 | membar #StoreLoad |
| 55 | .size membar_storeload, .-membar_storeload |
| 56 | |
| 57 | .globl membar_storeload_storestore |
| 58 | membar_storeload_storestore: |
| 59 | ba,pt %xcc, 99b |
| 60 | membar #StoreLoad | #StoreStore |
| 61 | .size membar_storeload_storestore, .-membar_storeload_storestore |
| 62 | |
| 63 | .globl membar_storeload_loadload |
| 64 | membar_storeload_loadload: |
| 65 | ba,pt %xcc, 99b |
| 66 | membar #StoreLoad | #LoadLoad |
| 67 | .size membar_storeload_loadload, .-membar_storeload_loadload |
| 68 | |
| 69 | .globl membar_storestore_loadstore |
| 70 | membar_storestore_loadstore: |
| 71 | ba,pt %xcc, 99b |
| 72 | membar #StoreStore | #LoadStore |
| 73 | .size membar_storestore_loadstore, .-membar_storestore_loadstore |