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Commit 966f4406 authored by Ralf Baechle's avatar Ralf Baechle
Browse files

[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: default avatarRalf Baechle <ralf@linux-mips.org>
parent 66a9a4ff

include/asm-mips/io.h

+15 −3
Original line number Diff line number Diff line
@@ -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