[MIPS] Work around bad code generation for <asm/io.h>.
If a call to set_io_port_base() was being followed by usage of
mips_io_port_base in the same function gcc was possibly using the old
value due to some clever abuse of const. Adding a barrier will keep
the optimization and result in correct code with latest gcc.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/include/asm-mips/io.h b/include/asm-mips/io.h
index 8c011aa..ba1d7bb 100644
--- a/include/asm-mips/io.h
+++ b/include/asm-mips/io.h
@@ -4,7 +4,7 @@
* for more details.
*
* Copyright (C) 1994, 1995 Waldorf GmbH
- * Copyright (C) 1994 - 2000 Ralf Baechle
+ * Copyright (C) 1994 - 2000, 06 Ralf Baechle
* Copyright (C) 1999, 2000 Silicon Graphics, Inc.
* Copyright (C) 2004, 2005 MIPS Technologies, Inc. All rights reserved.
* Author: Maciej W. Rozycki <macro@mips.com>
@@ -103,8 +103,20 @@
*/
extern const unsigned long mips_io_port_base;
-#define set_io_port_base(base) \
- do { * (unsigned long *) &mips_io_port_base = (base); } while (0)
+/*
+ * Gcc will generate code to load the value of mips_io_port_base after each
+ * function call which may be fairly wasteful in some cases. So we don't
+ * play quite by the book. We tell gcc mips_io_port_base is a long variable
+ * which solves the code generation issue. Now we need to violate the
+ * aliasing rules a little to make initialization possible and finally we
+ * will need the barrier() to fight side effects of the aliasing chat.
+ * This trickery will eventually collapse under gcc's optimizer. Oh well.
+ */
+static inline void set_io_port_base(unsigned long base)
+{
+ * (unsigned long *) &mips_io_port_base = base;
+ barrier();
+}
/*
* Thanks to James van Artsdalen for a better timing-fix than
