/* * include/asm-xtensa/rwsem.h * * This file is subject to the terms and conditions of the GNU General Public * License. See the file "COPYING" in the main directory of this archive * for more details. * * Largely copied from include/asm-ppc/rwsem.h * * Copyright (C) 2001 - 2005 Tensilica Inc. */ #ifndef _XTENSA_RWSEM_H #define _XTENSA_RWSEM_H #include <linux/list.h> #include <linux/spinlock.h> #include <asm/atomic.h> #include <asm/system.h> /* * the semaphore definition */ struct rw_semaphore { signed long count; #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) spinlock_t wait_lock; struct list_head wait_list; }; #define __RWSEM_INITIALIZER(name) \ { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \ LIST_HEAD_INIT((name).wait_list) } #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); } /* * lock for reading */ static inline void __down_read(struct rw_semaphore *sem) { if (atomic_add_return(1,(atomic_t *)(&sem->count)) > 0) smp_wmb(); else rwsem_down_read_failed(sem); } static inline int __down_read_trylock(struct rw_semaphore *sem) { int tmp; while ((tmp = sem->count) >= 0) { if (tmp == cmpxchg(&sem->count, tmp, tmp + RWSEM_ACTIVE_READ_BIAS)) { smp_wmb(); return 1; } } return 0; } /* * lock for writing */ static inline void __down_write(struct rw_semaphore *sem) { int tmp; tmp = atomic_add_return(RWSEM_ACTIVE_WRITE_BIAS, (atomic_t *)(&sem->count)); if (tmp == RWSEM_ACTIVE_WRITE_BIAS) smp_wmb(); else rwsem_down_write_failed(sem); } static inline int __down_write_trylock(struct rw_semaphore *sem) { int tmp; tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS); smp_wmb(); return tmp == RWSEM_UNLOCKED_VALUE; } /* * unlock after reading */ static inline void __up_read(struct rw_semaphore *sem) { int tmp; smp_wmb(); tmp = atomic_sub_return(1,(atomic_t *)(&sem->count)); if (tmp < -1 && (tmp & RWSEM_ACTIVE_MASK) == 0) rwsem_wake(sem); } /* * unlock after writing */ static inline void __up_write(struct rw_semaphore *sem) { smp_wmb(); if (atomic_sub_return(RWSEM_ACTIVE_WRITE_BIAS, (atomic_t *)(&sem->count)) < 0) rwsem_wake(sem); } /* * implement atomic add functionality */ static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem) { atomic_add(delta, (atomic_t *)(&sem->count)); } /* * downgrade write lock to read lock */ static inline void __downgrade_write(struct rw_semaphore *sem) { int tmp; smp_wmb(); tmp = atomic_add_return(-RWSEM_WAITING_BIAS, (atomic_t *)(&sem->count)); if (tmp < 0) rwsem_downgrade_wake(sem); } /* * implement exchange and add functionality */ static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem) { smp_mb(); return atomic_add_return(delta, (atomic_t *)(&sem->count)); } static inline int rwsem_is_locked(struct rw_semaphore *sem) { return (sem->count != 0); } #endif /* _XTENSA_RWSEM_H */