60 lines
2.1 KiB
Diff
60 lines
2.1 KiB
Diff
From: linux-mips@linux-mips.org
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Date: Wed, 15 Mar 2006 11:28:15 +0000
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To: git-commits@linux-mips.org
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Subject: [MIPS] Work around bad code generation for <asm/io.h>.
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Author: Ralf Baechle <ralf@linux-mips.org> Wed Mar 15 11:36:31 2006 +0000
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Commit: 6a186683e0a3d51836b6ef6b971508861c7002b5
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Gitweb: http://www.linux-mips.org/g/linux/6a186683
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Branch: master
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If a call to set_io_port_base() was being followed by usage of
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mips_io_port_base in the same function gcc was possibly using the old
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value due to some clever abuse of const. Adding a barrier will keep
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the optimization and result in correct code with latest gcc.
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Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
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---
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include/asm-mips/io.h | 18 +++++++++++++++---
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1 files changed, 15 insertions(+), 3 deletions(-)
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diff --git a/include/asm-mips/io.h b/include/asm-mips/io.h
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index 5c6d6ab..02995ad 100644
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--- a/include/asm-mips/io.h
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+++ b/include/asm-mips/io.h
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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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