Merge commit 'remotes/wd/master'

1 files changed, 15 insertions, 1 deletions

diff --git a/include/asm-mips/io.h b/include/asm-mips/io.h
index cd4d5dc9d9..1e060f7c31 100644
--- a/include/asm-mips/io.h
+++ b/include/asm-mips/io.h
@@ -71,7 +71,21 @@
  * instruction, so the lower 16 bits must be zero.  Should be true on
  * on any sane architecture; generic code does not use this assumption.
  */
-extern unsigned long mips_io_port_base;
+extern const unsigned long mips_io_port_base;
+
+/*
+ * 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;
+}
 
 /*
  * Thanks to James van Artsdalen for a better timing-fix than