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Diffstat (limited to 'arch/sparc/include/asm/barrier_64.h')
-rw-r--r--arch/sparc/include/asm/barrier_64.h56
1 files changed, 56 insertions, 0 deletions
diff --git a/arch/sparc/include/asm/barrier_64.h b/arch/sparc/include/asm/barrier_64.h
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+#ifndef __SPARC64_BARRIER_H
+#define __SPARC64_BARRIER_H
+
+/* 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.
+ */
+#define membar_safe(type) \
+do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \
+ " membar " type "\n" \
+ "1:\n" \
+ : : : "memory"); \
+} while (0)
+
+/* The kernel always executes in TSO memory model these days,
+ * and furthermore most sparc64 chips implement more stringent
+ * memory ordering than required by the specifications.
+ */
+#define mb() membar_safe("#StoreLoad")
+#define rmb() __asm__ __volatile__("":::"memory")
+#define wmb() __asm__ __volatile__("":::"memory")
+
+#define read_barrier_depends() do { } while(0)
+#define set_mb(__var, __value) \
+ do { __var = __value; membar_safe("#StoreLoad"); } while(0)
+
+#ifdef CONFIG_SMP
+#define smp_mb() mb()
+#define smp_rmb() rmb()
+#define smp_wmb() wmb()
+#else
+#define smp_mb() __asm__ __volatile__("":::"memory")
+#define smp_rmb() __asm__ __volatile__("":::"memory")
+#define smp_wmb() __asm__ __volatile__("":::"memory")
+#endif
+
+#define smp_read_barrier_depends() do { } while(0)
+
+#endif /* !(__SPARC64_BARRIER_H) */