/* * 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> * Copyright (C) 2005 Christoph Lameter <clameter@sgi.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 0xffffffff00000001 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 long count; spinlock_t wait_lock; struct list_head wait_list; #if RWSEM_DEBUG int debug; #endif }; #define RWSEM_UNLOCKED_VALUE __IA64_UL_CONST(0x0000000000000000) #define RWSEM_ACTIVE_BIAS __IA64_UL_CONST(0x0000000000000001) #define RWSEM_ACTIVE_MASK __IA64_UL_CONST(0x00000000ffffffff) #define RWSEM_WAITING_BIAS -__IA64_UL_CONST(0x0000000100000000) #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) { long result = ia64_fetchadd8_acq((unsigned long *)&sem->count, 1); if (result < 0) rwsem_down_read_failed(sem); } /* * lock for writing */ static inline void __down_write (struct rw_semaphore *sem) { long 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) { long result = ia64_fetchadd8_rel((unsigned long *)&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) { long 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) { long 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) { long 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) { long 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) atomic64_add(delta, (atomic64_t *)(&(sem)->count)) #define rwsem_atomic_update(delta, sem) atomic64_add_return(delta, (atomic64_t *)(&(sem)->count)) static inline int rwsem_is_locked(struct rw_semaphore *sem) { return (sem->count != 0); } #endif /* _ASM_IA64_RWSEM_H */