From a88d970c8bb55dc20f319ce3e33c7ce0e9647480 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 17 Mar 2024 14:44:38 -0700 Subject: lib: Add one-byte emulation function 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 Acked-by: Marco Elver Cc: Andrew Morton Cc: Thomas Gleixner Cc: "Peter Zijlstra (Intel)" Cc: Douglas Anderson Cc: Petr Mladek Cc: Arnd Bergmann Cc: --- include/linux/cmpxchg-emu.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) create mode 100644 include/linux/cmpxchg-emu.h (limited to 'include/linux') diff --git a/include/linux/cmpxchg-emu.h b/include/linux/cmpxchg-emu.h new file mode 100644 index 000000000000..998deec67740 --- /dev/null +++ b/include/linux/cmpxchg-emu.h @@ -0,0 +1,15 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Emulated 1-byte and 2-byte cmpxchg operations for architectures + * lacking direct support for these sizes. These are implemented in terms + * of 4-byte cmpxchg operations. + * + * Copyright (C) 2024 Paul E. McKenney. + */ + +#ifndef __LINUX_CMPXCHG_EMU_H +#define __LINUX_CMPXCHG_EMU_H + +uintptr_t cmpxchg_emu_u8(volatile u8 *p, uintptr_t old, uintptr_t new); + +#endif /* __LINUX_CMPXCHG_EMU_H */ -- cgit v1.2.3