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authorLinus Torvalds <torvalds@linux-foundation.org>2008-08-03 13:39:02 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-08-03 13:39:02 -0400
commit7e31aa11fc672bbe0dd0da59513c9efe3809ced7 (patch)
tree0aafe6a0045230950ce6b26579a053da12614a49 /arch/arm/include/asm/mutex.h
parent071f4924844c435a3ae0cdbab7d7df2f1da85713 (diff)
parent9cb7117fa4858468014f76bd996076985111e955 (diff)
Merge branch 'for-linus' of master.kernel.org:/home/rmk/linux-2.6-arm
* 'for-linus' of master.kernel.org:/home/rmk/linux-2.6-arm: [ARM] 5182/1: pxa: Fix pcm990 compilation [ARM] Fix explicit asm(-arm)?/arch-foo references [ARM] move include/asm-arm to arch/arm/include/asm [ARM] Remove explicit dependency for misc.o from compressed/Makefile [ARM] initrd: claim initrd memory exclusively [ARM] pxa: add support for L2 outer cache on XScale3 (attempt 2) [ARM] 5180/1: at91: Fix at91_nand -> atmel_nand rename fallout [ARM] add Sascha Hauer as Freescale i.MX Maintainer [ARM] i.MX: add missing clock functions exports [ARM] i.MX: remove set_imx_fb_info() export [ARM] mx1ads: make mmc platform data available for modules [ARM] mx2: add missing Kconfig dependency
Diffstat (limited to 'arch/arm/include/asm/mutex.h')
-rw-r--r--arch/arm/include/asm/mutex.h127
1 files changed, 127 insertions, 0 deletions
diff --git a/arch/arm/include/asm/mutex.h b/arch/arm/include/asm/mutex.h
new file mode 100644
index 000000000000..93226cf23ae0
--- /dev/null
+++ b/arch/arm/include/asm/mutex.h
@@ -0,0 +1,127 @@
1/*
2 * arch/arm/include/asm/mutex.h
3 *
4 * ARM optimized mutex locking primitives
5 *
6 * Please look into asm-generic/mutex-xchg.h for a formal definition.
7 */
8#ifndef _ASM_MUTEX_H
9#define _ASM_MUTEX_H
10
11#if __LINUX_ARM_ARCH__ < 6
12/* On pre-ARMv6 hardware the swp based implementation is the most efficient. */
13# include <asm-generic/mutex-xchg.h>
14#else
15
16/*
17 * Attempting to lock a mutex on ARMv6+ can be done with a bastardized
18 * atomic decrement (it is not a reliable atomic decrement but it satisfies
19 * the defined semantics for our purpose, while being smaller and faster
20 * than a real atomic decrement or atomic swap. The idea is to attempt
21 * decrementing the lock value only once. If once decremented it isn't zero,
22 * or if its store-back fails due to a dispute on the exclusive store, we
23 * simply bail out immediately through the slow path where the lock will be
24 * reattempted until it succeeds.
25 */
26static inline void
27__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
28{
29 int __ex_flag, __res;
30
31 __asm__ (
32
33 "ldrex %0, [%2] \n\t"
34 "sub %0, %0, #1 \n\t"
35 "strex %1, %0, [%2] "
36
37 : "=&r" (__res), "=&r" (__ex_flag)
38 : "r" (&(count)->counter)
39 : "cc","memory" );
40
41 __res |= __ex_flag;
42 if (unlikely(__res != 0))
43 fail_fn(count);
44}
45
46static inline int
47__mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *))
48{
49 int __ex_flag, __res;
50
51 __asm__ (
52
53 "ldrex %0, [%2] \n\t"
54 "sub %0, %0, #1 \n\t"
55 "strex %1, %0, [%2] "
56
57 : "=&r" (__res), "=&r" (__ex_flag)
58 : "r" (&(count)->counter)
59 : "cc","memory" );
60
61 __res |= __ex_flag;
62 if (unlikely(__res != 0))
63 __res = fail_fn(count);
64 return __res;
65}
66
67/*
68 * Same trick is used for the unlock fast path. However the original value,
69 * rather than the result, is used to test for success in order to have
70 * better generated assembly.
71 */
72static inline void
73__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
74{
75 int __ex_flag, __res, __orig;
76
77 __asm__ (
78
79 "ldrex %0, [%3] \n\t"
80 "add %1, %0, #1 \n\t"
81 "strex %2, %1, [%3] "
82
83 : "=&r" (__orig), "=&r" (__res), "=&r" (__ex_flag)
84 : "r" (&(count)->counter)
85 : "cc","memory" );
86
87 __orig |= __ex_flag;
88 if (unlikely(__orig != 0))
89 fail_fn(count);
90}
91
92/*
93 * If the unlock was done on a contended lock, or if the unlock simply fails
94 * then the mutex remains locked.
95 */
96#define __mutex_slowpath_needs_to_unlock() 1
97
98/*
99 * For __mutex_fastpath_trylock we use another construct which could be
100 * described as a "single value cmpxchg".
101 *
102 * This provides the needed trylock semantics like cmpxchg would, but it is
103 * lighter and less generic than a true cmpxchg implementation.
104 */
105static inline int
106__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
107{
108 int __ex_flag, __res, __orig;
109
110 __asm__ (
111
112 "1: ldrex %0, [%3] \n\t"
113 "subs %1, %0, #1 \n\t"
114 "strexeq %2, %1, [%3] \n\t"
115 "movlt %0, #0 \n\t"
116 "cmpeq %2, #0 \n\t"
117 "bgt 1b "
118
119 : "=&r" (__orig), "=&r" (__res), "=&r" (__ex_flag)
120 : "r" (&count->counter)
121 : "cc", "memory" );
122
123 return __orig;
124}
125
126#endif
127#endif