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[MIPS] Work around bad code generation for <asm/io.h>.

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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>
This commit is contained in:
Ralf Baechle 2006-03-15 11:36:31 +00:00
parent 66a9a4ffda
commit 966f4406d9
1 changed files with 15 additions and 3 deletions
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18
include/asm-mips/io.h
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@ -4,7 +4,7 @@
* for more details. * for more details.
* *
* Copyright (C) 1994, 1995 Waldorf GmbH * 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) 1999, 2000 Silicon Graphics, Inc.
* Copyright (C) 2004, 2005 MIPS Technologies, Inc. All rights reserved. * Copyright (C) 2004, 2005 MIPS Technologies, Inc. All rights reserved.
* Author: Maciej W. Rozycki <macro@mips.com> * Author: Maciej W. Rozycki <macro@mips.com>
@ -103,8 +103,20 @@
*/ */
extern const unsigned long mips_io_port_base; 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 * Thanks to James van Artsdalen for a better timing-fix than