forked from mirrors/linux
a88d970c8b
Architectures are required to provide four-byte cmpxchg() and 64-bit architectures are additionally required to provide eight-byte cmpxchg(). However, there are cases where one-byte cmpxchg() would be extremely useful. Therefore, provide cmpxchg_emu_u8() that emulates one-byte cmpxchg() in terms of four-byte cmpxchg(). Note that this emulations is fully ordered, and can (for example) cause one-byte cmpxchg_relaxed() to incur the overhead of full ordering. If this causes problems for a given architecture, that architecture is free to provide its own lighter-weight primitives. [ paulmck: Apply Marco Elver feedback. ] [ paulmck: Apply kernel test robot feedback. ] [ paulmck: Drop two-byte support per Arnd Bergmann feedback. ] Link: https://lore.kernel.org/all/0733eb10-5e7a-4450-9b8a-527b97c842ff@paulmck-laptop/ Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Acked-by: Marco Elver <elver@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org> Cc: Douglas Anderson <dianders@chromium.org> Cc: Petr Mladek <pmladek@suse.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: <linux-arch@vger.kernel.org>
15 lines
435 B
C
15 lines
435 B
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* Emulated 1-byte and 2-byte cmpxchg operations for architectures
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* lacking direct support for these sizes. These are implemented in terms
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* of 4-byte cmpxchg operations.
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*
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* Copyright (C) 2024 Paul E. McKenney.
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*/
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#ifndef __LINUX_CMPXCHG_EMU_H
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#define __LINUX_CMPXCHG_EMU_H
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uintptr_t cmpxchg_emu_u8(volatile u8 *p, uintptr_t old, uintptr_t new);
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#endif /* __LINUX_CMPXCHG_EMU_H */
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