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Diffstat (limited to 'include/asm-ia64/rwsem.h')
| -rw-r--r-- | include/asm-ia64/rwsem.h | 188 |
1 files changed, 188 insertions, 0 deletions
diff --git a/include/asm-ia64/rwsem.h b/include/asm-ia64/rwsem.h new file mode 100644 index 0000000..6ece506 --- /dev/null +++ b/include/asm-ia64/rwsem.h @@ -0,0 +1,188 @@ +/* + * asm-ia64/rwsem.h: R/W semaphores for ia64 + * + * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com> + * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com> + * + * Based on asm-i386/rwsem.h and other architecture implementation. + * + * The MSW of the count is the negated number of active writers and + * waiting lockers, and the LSW is the total number of active locks. + * + * The lock count is initialized to 0 (no active and no waiting lockers). + * + * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case + * of an uncontended lock. Readers increment by 1 and see a positive value + * when uncontended, negative if there are writers (and maybe) readers + * waiting (in which case it goes to sleep). + */ + +#ifndef _ASM_IA64_RWSEM_H +#define _ASM_IA64_RWSEM_H + +#include <linux/list.h> +#include <linux/spinlock.h> + +#include <asm/intrinsics.h> + +/* + * the semaphore definition + */ +struct rw_semaphore { + signed int count; + spinlock_t wait_lock; + struct list_head wait_list; +#if RWSEM_DEBUG + int debug; +#endif +}; + +#define RWSEM_UNLOCKED_VALUE 0x00000000 +#define RWSEM_ACTIVE_BIAS 0x00000001 +#define RWSEM_ACTIVE_MASK 0x0000ffff +#define RWSEM_WAITING_BIAS (-0x00010000) +#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS +#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS) + +/* + * initialization + */ +#if RWSEM_DEBUG +#define __RWSEM_DEBUG_INIT , 0 +#else +#define __RWSEM_DEBUG_INIT /* */ +#endif + +#define __RWSEM_INITIALIZER(name) \ + { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \ + LIST_HEAD_INIT((name).wait_list) \ + __RWSEM_DEBUG_INIT } + +#define DECLARE_RWSEM(name) \ + struct rw_semaphore name = __RWSEM_INITIALIZER(name) + +extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); +extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); +extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem); +extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); + +static inline void +init_rwsem (struct rw_semaphore *sem) +{ + sem->count = RWSEM_UNLOCKED_VALUE; + spin_lock_init(&sem->wait_lock); + INIT_LIST_HEAD(&sem->wait_list); +#if RWSEM_DEBUG + sem->debug = 0; +#endif +} + +/* + * lock for reading + */ +static inline void +__down_read (struct rw_semaphore *sem) +{ + int result = ia64_fetchadd4_acq((unsigned int *)&sem->count, 1); + + if (result < 0) + rwsem_down_read_failed(sem); +} + +/* + * lock for writing + */ +static inline void +__down_write (struct rw_semaphore *sem) +{ + int old, new; + + do { + old = sem->count; + new = old + RWSEM_ACTIVE_WRITE_BIAS; + } while (cmpxchg_acq(&sem->count, old, new) != old); + + if (old != 0) + rwsem_down_write_failed(sem); +} + +/* + * unlock after reading + */ +static inline void +__up_read (struct rw_semaphore *sem) +{ + int result = ia64_fetchadd4_rel((unsigned int *)&sem->count, -1); + + if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0) + rwsem_wake(sem); +} + +/* + * unlock after writing + */ +static inline void +__up_write (struct rw_semaphore *sem) +{ + int old, new; + + do { + old = sem->count; + new = old - RWSEM_ACTIVE_WRITE_BIAS; + } while (cmpxchg_rel(&sem->count, old, new) != old); + + if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0) + rwsem_wake(sem); +} + +/* + * trylock for reading -- returns 1 if successful, 0 if contention + */ +static inline int +__down_read_trylock (struct rw_semaphore *sem) +{ + int tmp; + while ((tmp = sem->count) >= 0) { + if (tmp == cmpxchg_acq(&sem->count, tmp, tmp+1)) { + return 1; + } + } + return 0; +} + +/* + * trylock for writing -- returns 1 if successful, 0 if contention + */ +static inline int +__down_write_trylock (struct rw_semaphore *sem) +{ + int tmp = cmpxchg_acq(&sem->count, RWSEM_UNLOCKED_VALUE, + RWSEM_ACTIVE_WRITE_BIAS); + return tmp == RWSEM_UNLOCKED_VALUE; +} + +/* + * downgrade write lock to read lock + */ +static inline void +__downgrade_write (struct rw_semaphore *sem) +{ + int old, new; + + do { + old = sem->count; + new = old - RWSEM_WAITING_BIAS; + } while (cmpxchg_rel(&sem->count, old, new) != old); + + if (old < 0) + rwsem_downgrade_wake(sem); +} + +/* + * Implement atomic add functionality. These used to be "inline" functions, but GCC v3.1 + * doesn't quite optimize this stuff right and ends up with bad calls to fetchandadd. + */ +#define rwsem_atomic_add(delta, sem) atomic_add(delta, (atomic_t *)(&(sem)->count)) +#define rwsem_atomic_update(delta, sem) atomic_add_return(delta, (atomic_t *)(&(sem)->count)) + +#endif /* _ASM_IA64_RWSEM_H */ |
