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[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>
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1 changed files with 15 additions and 3 deletions
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@ -4,7 +4,7 @@
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* for more details.
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*
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* Copyright (C) 1994, 1995 Waldorf GmbH
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* Copyright (C) 1994 - 2000 Ralf Baechle
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* Copyright (C) 1994 - 2000, 06 Ralf Baechle
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* Copyright (C) 1999, 2000 Silicon Graphics, Inc.
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* Copyright (C) 2004, 2005 MIPS Technologies, Inc. All rights reserved.
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* Author: Maciej W. Rozycki <macro@mips.com>
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@ -103,8 +103,20 @@
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*/
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extern const unsigned long mips_io_port_base;
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#define set_io_port_base(base) \
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do { * (unsigned long *) &mips_io_port_base = (base); } while (0)
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/*
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* Gcc will generate code to load the value of mips_io_port_base after each
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* function call which may be fairly wasteful in some cases. So we don't
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* play quite by the book. We tell gcc mips_io_port_base is a long variable
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* which solves the code generation issue. Now we need to violate the
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* aliasing rules a little to make initialization possible and finally we
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* will need the barrier() to fight side effects of the aliasing chat.
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* This trickery will eventually collapse under gcc's optimizer. Oh well.
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*/
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static inline void set_io_port_base(unsigned long base)
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{
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* (unsigned long *) &mips_io_port_base = base;
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barrier();
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}
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/*
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* Thanks to James van Artsdalen for a better timing-fix than
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