From 57f0f512b273f60d52568b8c6b77e17f5636edc0 Mon Sep 17 00:00:00 2001 From: André Fabian Silva Delgado Date: Wed, 5 Aug 2015 17:04:01 -0300 Subject: Initial import --- arch/arc/include/asm/cmpxchg.h | 161 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 161 insertions(+) create mode 100644 arch/arc/include/asm/cmpxchg.h (limited to 'arch/arc/include/asm/cmpxchg.h') diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h new file mode 100644 index 000000000..44fd531f4 --- /dev/null +++ b/arch/arc/include/asm/cmpxchg.h @@ -0,0 +1,161 @@ +/* + * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#ifndef __ASM_ARC_CMPXCHG_H +#define __ASM_ARC_CMPXCHG_H + +#include + +#include +#include + +#ifdef CONFIG_ARC_HAS_LLSC + +static inline unsigned long +__cmpxchg(volatile void *ptr, unsigned long expected, unsigned long new) +{ + unsigned long prev; + + /* + * Explicit full memory barrier needed before/after as + * LLOCK/SCOND thmeselves don't provide any such semantics + */ + smp_mb(); + + __asm__ __volatile__( + "1: llock %0, [%1] \n" + " brne %0, %2, 2f \n" + " scond %3, [%1] \n" + " bnz 1b \n" + "2: \n" + : "=&r"(prev) /* Early clobber, to prevent reg reuse */ + : "r"(ptr), /* Not "m": llock only supports reg direct addr mode */ + "ir"(expected), + "r"(new) /* can't be "ir". scond can't take LIMM for "b" */ + : "cc", "memory"); /* so that gcc knows memory is being written here */ + + smp_mb(); + + return prev; +} + +#else + +static inline unsigned long +__cmpxchg(volatile void *ptr, unsigned long expected, unsigned long new) +{ + unsigned long flags; + int prev; + volatile unsigned long *p = ptr; + + /* + * spin lock/unlock provide the needed smp_mb() before/after + */ + atomic_ops_lock(flags); + prev = *p; + if (prev == expected) + *p = new; + atomic_ops_unlock(flags); + return prev; +} + +#endif /* CONFIG_ARC_HAS_LLSC */ + +#define cmpxchg(ptr, o, n) ((typeof(*(ptr)))__cmpxchg((ptr), \ + (unsigned long)(o), (unsigned long)(n))) + +/* + * Since not supported natively, ARC cmpxchg() uses atomic_ops_lock (UP/SMP) + * just to gaurantee semantics. + * atomic_cmpxchg() needs to use the same locks as it's other atomic siblings + * which also happens to be atomic_ops_lock. + * + * Thus despite semantically being different, implementation of atomic_cmpxchg() + * is same as cmpxchg(). + */ +#define atomic_cmpxchg(v, o, n) ((int)cmpxchg(&((v)->counter), (o), (n))) + + +/* + * xchg (reg with memory) based on "Native atomic" EX insn + */ +static inline unsigned long __xchg(unsigned long val, volatile void *ptr, + int size) +{ + extern unsigned long __xchg_bad_pointer(void); + + switch (size) { + case 4: + smp_mb(); + + __asm__ __volatile__( + " ex %0, [%1] \n" + : "+r"(val) + : "r"(ptr) + : "memory"); + + smp_mb(); + + return val; + } + return __xchg_bad_pointer(); +} + +#define _xchg(ptr, with) ((typeof(*(ptr)))__xchg((unsigned long)(with), (ptr), \ + sizeof(*(ptr)))) + +/* + * On ARC700, EX insn is inherently atomic, so by default "vanilla" xchg() need + * not require any locking. However there's a quirk. + * ARC lacks native CMPXCHG, thus emulated (see above), using external locking - + * incidently it "reuses" the same atomic_ops_lock used by atomic APIs. + * Now, llist code uses cmpxchg() and xchg() on same data, so xchg() needs to + * abide by same serializing rules, thus ends up using atomic_ops_lock as well. + * + * This however is only relevant if SMP and/or ARC lacks LLSC + * if (UP or LLSC) + * xchg doesn't need serialization + * else <==> !(UP or LLSC) <==> (!UP and !LLSC) <==> (SMP and !LLSC) + * xchg needs serialization + */ + +#if !defined(CONFIG_ARC_HAS_LLSC) && defined(CONFIG_SMP) + +#define xchg(ptr, with) \ +({ \ + unsigned long flags; \ + typeof(*(ptr)) old_val; \ + \ + atomic_ops_lock(flags); \ + old_val = _xchg(ptr, with); \ + atomic_ops_unlock(flags); \ + old_val; \ +}) + +#else + +#define xchg(ptr, with) _xchg(ptr, with) + +#endif + +/* + * "atomic" variant of xchg() + * REQ: It needs to follow the same serialization rules as other atomic_xxx() + * Since xchg() doesn't always do that, it would seem that following defintion + * is incorrect. But here's the rationale: + * SMP : Even xchg() takes the atomic_ops_lock, so OK. + * LLSC: atomic_ops_lock are not relevent at all (even if SMP, since LLSC + * is natively "SMP safe", no serialization required). + * UP : other atomics disable IRQ, so no way a difft ctxt atomic_xchg() + * could clobber them. atomic_xchg() itself would be 1 insn, so it + * can't be clobbered by others. Thus no serialization required when + * atomic_xchg is involved. + */ +#define atomic_xchg(v, new) (xchg(&((v)->counter), new)) + +#endif -- cgit v1.2.3-54-g00ecf