1/*
  2 * Assembly implementation of the mutex fastpath, based on atomic
  3 * decrement/increment.
  4 *
  5 * started by Ingo Molnar:
  6 *
  7 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
  8 */
  9#ifndef _ASM_X86_MUTEX_64_H
 10#define _ASM_X86_MUTEX_64_H
 11
 12/**
 13 * __mutex_fastpath_lock - decrement and call function if negative
 14 * @v: pointer of type atomic_t
 15 * @fail_fn: function to call if the result is negative
 16 *
 17 * Atomically decrements @v and calls <fail_fn> if the result is negative.
 18 */
 19#ifdef CC_HAVE_ASM_GOTO
 20static inline void __mutex_fastpath_lock(atomic_t *v,
 21					 void (*fail_fn)(atomic_t *))
 22{
 23	asm_volatile_goto(LOCK_PREFIX "   decl %0\n"
 24			  "   jns %l[exit]\n"
 25			  : : "m" (v->counter)
 26			  : "memory", "cc"
 27			  : exit);
 28	fail_fn(v);
 29exit:
 30	return;
 31}
 32#else
 33#define __mutex_fastpath_lock(v, fail_fn)			\
 34do {								\
 35	unsigned long dummy;					\
 36								\
 37	typecheck(atomic_t *, v);				\
 38	typecheck_fn(void (*)(atomic_t *), fail_fn);		\
 39								\
 40	asm volatile(LOCK_PREFIX "   decl (%%rdi)\n"		\
 41		     "   jns 1f		\n"			\
 42		     "   call " #fail_fn "\n"			\
 43		     "1:"					\
 44		     : "=D" (dummy)				\
 45		     : "D" (v)					\
 46		     : "rax", "rsi", "rdx", "rcx",		\
 47		       "r8", "r9", "r10", "r11", "memory");	\
 48} while (0)
 49#endif
 50
 51/**
 52 *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
 53 *                                 from 1 to a 0 value
 54 *  @count: pointer of type atomic_t
 55 *
 56 * Change the count from 1 to a value lower than 1. This function returns 0
 57 * if the fastpath succeeds, or -1 otherwise.
 58 */
 59static inline int __mutex_fastpath_lock_retval(atomic_t *count)
 60{
 61	if (unlikely(atomic_dec_return(count) < 0))
 62		return -1;
 63	else
 64		return 0;
 65}
 66
 67/**
 68 * __mutex_fastpath_unlock - increment and call function if nonpositive
 69 * @v: pointer of type atomic_t
 70 * @fail_fn: function to call if the result is nonpositive
 71 *
 72 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
 73 */
 74#ifdef CC_HAVE_ASM_GOTO
 75static inline void __mutex_fastpath_unlock(atomic_t *v,
 76					   void (*fail_fn)(atomic_t *))
 77{
 78	asm_volatile_goto(LOCK_PREFIX "   incl %0\n"
 79			  "   jg %l[exit]\n"
 80			  : : "m" (v->counter)
 81			  : "memory", "cc"
 82			  : exit);
 83	fail_fn(v);
 84exit:
 85	return;
 86}
 87#else
 88#define __mutex_fastpath_unlock(v, fail_fn)			\
 89do {								\
 90	unsigned long dummy;					\
 91								\
 92	typecheck(atomic_t *, v);				\
 93	typecheck_fn(void (*)(atomic_t *), fail_fn);		\
 94								\
 95	asm volatile(LOCK_PREFIX "   incl (%%rdi)\n"		\
 96		     "   jg 1f\n"				\
 97		     "   call " #fail_fn "\n"			\
 98		     "1:"					\
 99		     : "=D" (dummy)				\
100		     : "D" (v)					\
101		     : "rax", "rsi", "rdx", "rcx",		\
102		       "r8", "r9", "r10", "r11", "memory");	\
103} while (0)
104#endif
105
106#define __mutex_slowpath_needs_to_unlock()	1
107
108/**
109 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
110 *
111 *  @count: pointer of type atomic_t
112 *  @fail_fn: fallback function
113 *
114 * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
115 * if it wasn't 1 originally. [the fallback function is never used on
116 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
117 */
118static inline int __mutex_fastpath_trylock(atomic_t *count,
119					   int (*fail_fn)(atomic_t *))
120{
121	if (likely(atomic_cmpxchg(count, 1, 0) == 1))
122		return 1;
123	else
124		return 0;
125}
126
127#endif /* _ASM_X86_MUTEX_64_H */