[MIPS] Cleanup memory barriers for weakly ordered systems.

Also the R4000 / R4600 LL/SC instructions imply a sync so no explicit sync
needed.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 132 insertions, 0 deletions

diff --git a/include/asm-mips/barrier.h b/include/asm-mips/barrier.h
new file mode 100644
index 00000000000..ed82631b001
--- /dev/null
+++ b/include/asm-mips/barrier.h
@@ -0,0 +1,132 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2006 by Ralf Baechle (ralf@linux-mips.org)
+ */
+#ifndef __ASM_BARRIER_H
+#define __ASM_BARRIER_H
+
+/*
+ * read_barrier_depends - Flush all pending reads that subsequents reads
+ * depend on.
+ *
+ * No data-dependent reads from memory-like regions are ever reordered
+ * over this barrier.  All reads preceding this primitive are guaranteed
+ * to access memory (but not necessarily other CPUs' caches) before any
+ * reads following this primitive that depend on the data return by
+ * any of the preceding reads.  This primitive is much lighter weight than
+ * rmb() on most CPUs, and is never heavier weight than is
+ * rmb().
+ *
+ * These ordering constraints are respected by both the local CPU
+ * and the compiler.
+ *
+ * Ordering is not guaranteed by anything other than these primitives,
+ * not even by data dependencies.  See the documentation for
+ * memory_barrier() for examples and URLs to more information.
+ *
+ * For example, the following code would force ordering (the initial
+ * value of "a" is zero, "b" is one, and "p" is "&a"):
+ *
+ * <programlisting>
+ *	CPU 0				CPU 1
+ *
+ *	b = 2;
+ *	memory_barrier();
+ *	p = &b;				q = p;
+ *					read_barrier_depends();
+ *					d = *q;
+ * </programlisting>
+ *
+ * because the read of "*q" depends on the read of "p" and these
+ * two reads are separated by a read_barrier_depends().  However,
+ * the following code, with the same initial values for "a" and "b":
+ *
+ * <programlisting>
+ *	CPU 0				CPU 1
+ *
+ *	a = 2;
+ *	memory_barrier();
+ *	b = 3;				y = b;
+ *					read_barrier_depends();
+ *					x = a;
+ * </programlisting>
+ *
+ * does not enforce ordering, since there is no data dependency between
+ * the read of "a" and the read of "b".  Therefore, on some CPUs, such
+ * as Alpha, "y" could be set to 3 and "x" to 0.  Use rmb()
+ * in cases like this where there are no data dependencies.
+ */
+
+#define read_barrier_depends()		do { } while(0)
+#define smp_read_barrier_depends()	do { } while(0)
+
+#ifdef CONFIG_CPU_HAS_SYNC
+#define __sync()				\
+	__asm__ __volatile__(			\
+		".set	push\n\t"		\
+		".set	noreorder\n\t"		\
+		".set	mips2\n\t"		\
+		"sync\n\t"			\
+		".set	pop"			\
+		: /* no output */		\
+		: /* no input */		\
+		: "memory")
+#else
+#define __sync()	do { } while(0)
+#endif
+
+#define __fast_iob()				\
+	__asm__ __volatile__(			\
+		".set	push\n\t"		\
+		".set	noreorder\n\t"		\
+		"lw	$0,%0\n\t"		\
+		"nop\n\t"			\
+		".set	pop"			\
+		: /* no output */		\
+		: "m" (*(int *)CKSEG1)		\
+		: "memory")
+
+#define fast_wmb()	__sync()
+#define fast_rmb()	__sync()
+#define fast_mb()	__sync()
+#define fast_iob()				\
+	do {					\
+		__sync();			\
+		__fast_iob();			\
+	} while (0)
+
+#ifdef CONFIG_CPU_HAS_WB
+
+#include <asm/wbflush.h>
+
+#define wmb()		fast_wmb()
+#define rmb()		fast_rmb()
+#define mb()		wbflush()
+#define iob()		wbflush()
+
+#else /* !CONFIG_CPU_HAS_WB */
+
+#define wmb()		fast_wmb()
+#define rmb()		fast_rmb()
+#define mb()		fast_mb()
+#define iob()		fast_iob()
+
+#endif /* !CONFIG_CPU_HAS_WB */
+
+#if defined(CONFIG_WEAK_ORDERING) && defined(CONFIG_SMP)
+#define __WEAK_ORDERING_MB	"       sync	\n"
+#else
+#define __WEAK_ORDERING_MB	"		\n"
+#endif
+
+#define smp_mb()	__asm__ __volatile__(__WEAK_ORDERING_MB : : :"memory")
+#define smp_rmb()	__asm__ __volatile__(__WEAK_ORDERING_MB : : :"memory")
+#define smp_wmb()	__asm__ __volatile__(__WEAK_ORDERING_MB : : :"memory")
+
+#define set_mb(var, value) \
+	do { var = value; smp_mb(); } while (0)
+
+#endif /* __ASM_BARRIER_H */