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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /include/asm-ia64/rwsem.h
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Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'include/asm-ia64/rwsem.h')
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diff --git a/include/asm-ia64/rwsem.h b/include/asm-ia64/rwsem.h
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+/*
+ * 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 */
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