[SPARC64]: More fully work around Spitfire Errata 51.
It appears that a memory barrier soon after a mispredicted
branch, not just in the delay slot, can cause the hang
condition of this cpu errata.
So move them out-of-line, and explicitly put them into
a "branch always, predict taken" delay slot which should
fully kill this problem.
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/arch/sparc64/lib/mb.S b/arch/sparc64/lib/mb.S
new file mode 100644
index 0000000..4004f74
--- /dev/null
+++ b/arch/sparc64/lib/mb.S
@@ -0,0 +1,73 @@
+/* mb.S: Out of line memory barriers.
+ *
+ * Copyright (C) 2005 David S. Miller (davem@davemloft.net)
+ */
+
+ /* These are here in an effort to more fully work around
+ * Spitfire Errata #51. Essentially, if a memory barrier
+ * occurs soon after a mispredicted branch, the chip can stop
+ * executing instructions until a trap occurs. Therefore, if
+ * interrupts are disabled, the chip can hang forever.
+ *
+ * It used to be believed that the memory barrier had to be
+ * right in the delay slot, but a case has been traced
+ * recently wherein the memory barrier was one instruction
+ * after the branch delay slot and the chip still hung. The
+ * offending sequence was the following in sym_wakeup_done()
+ * of the sym53c8xx_2 driver:
+ *
+ * call sym_ccb_from_dsa, 0
+ * movge %icc, 0, %l0
+ * brz,pn %o0, .LL1303
+ * mov %o0, %l2
+ * membar #LoadLoad
+ *
+ * The branch has to be mispredicted for the bug to occur.
+ * Therefore, we put the memory barrier explicitly into a
+ * "branch always, predicted taken" delay slot to avoid the
+ * problem case.
+ */
+
+ .text
+
+99: retl
+ nop
+
+ .globl mb
+mb: ba,pt %xcc, 99b
+ membar #LoadLoad | #LoadStore | #StoreStore | #StoreLoad
+ .size mb, .-mb
+
+ .globl rmb
+rmb: ba,pt %xcc, 99b
+ membar #LoadLoad
+ .size rmb, .-rmb
+
+ .globl wmb
+wmb: ba,pt %xcc, 99b
+ membar #StoreStore
+ .size wmb, .-wmb
+
+ .globl membar_storeload
+membar_storeload:
+ ba,pt %xcc, 99b
+ membar #StoreLoad
+ .size membar_storeload, .-membar_storeload
+
+ .globl membar_storeload_storestore
+membar_storeload_storestore:
+ ba,pt %xcc, 99b
+ membar #StoreLoad | #StoreStore
+ .size membar_storeload_storestore, .-membar_storeload_storestore
+
+ .globl membar_storeload_loadload
+membar_storeload_loadload:
+ ba,pt %xcc, 99b
+ membar #StoreLoad | #LoadLoad
+ .size membar_storeload_loadload, .-membar_storeload_loadload
+
+ .globl membar_storestore_loadstore
+membar_storestore_loadstore:
+ ba,pt %xcc, 99b
+ membar #StoreStore | #LoadStore
+ .size membar_storestore_loadstore, .-membar_storestore_loadstore