Merge with Linux 2.3.41.

1 files changed, 173 insertions, 3 deletions

diff --git a/include/asm-mips/semaphore.h b/include/asm-mips/semaphore.h
index 433c3b862..6a0fab080 100644
--- a/include/asm-mips/semaphore.h
+++ b/include/asm-mips/semaphore.h
@@ -1,4 +1,4 @@
-/* $Id: semaphore.h,v 1.11 1999/10/20 21:10:58 ralf Exp $
+/* $Id: semaphore.h,v 1.12 1999/12/08 22:05:10 harald Exp $
  *
  * SMP- and interrupt-safe semaphores..
  *
@@ -7,8 +7,8 @@
  * for more details.
  *
  * (C) Copyright 1996  Linus Torvalds
- * (C) Copyright 1998, 1999  Ralf Baechle
- * (C) Copyright 1999  Silicon Graphics, Inc.
+ * (C) Copyright 1998, 1999, 2000  Ralf Baechle
+ * (C) Copyright 1999, 2000  Silicon Graphics, Inc.
  */
 #ifndef _ASM_SEMAPHORE_H
 #define _ASM_SEMAPHORE_H
@@ -189,4 +189,174 @@ extern inline void up(struct semaphore * sem)
 		__up(sem);
 }
 
+/*
+ * rw mutexes (should that be mutices? =) -- throw rw spinlocks and
+ * semaphores together, and this is what we end up with...
+ *
+ * The lock is initialized to BIAS.  This way, a writer subtracts BIAS ands
+ * gets 0 for the case of an uncontended lock.  Readers decrement by 1 and
+ * see a positive value when uncontended, negative if there are writers
+ * waiting (in which case it goes to sleep).
+ *
+ * The value 0x01000000 supports up to 128 processors and lots of processes.
+ * BIAS must be chosen such that subtracting BIAS once per CPU will result
+ * in the int remaining negative.  In terms of fairness, this should result
+ * in the lock flopping back and forth between readers and writers under
+ * heavy use.
+ *
+ * Once we start supporting machines with more than 128 CPUs, we should go
+ * for using a 64bit atomic type instead of 32bit as counter. We shall
+ * probably go for bias 0x80000000 then, so that single sethi can set it.
+ * */
+
+#define RW_LOCK_BIAS		0x01000000
+
+struct rw_semaphore {
+	atomic_t		count;
+	/* bit 0 means read bias granted;
+	   bit 1 means write bias granted.  */
+	unsigned		granted;
+	wait_queue_head_t	wait;
+	wait_queue_head_t	write_bias_wait;
+#if WAITQUEUE_DEBUG
+	long			__magic;
+	atomic_t		readers;
+	atomic_t		writers;
+#endif
+};
+
+#if WAITQUEUE_DEBUG
+#define __RWSEM_DEBUG_INIT	, ATOMIC_INIT(0), ATOMIC_INIT(0)
+#else
+#define __RWSEM_DEBUG_INIT	/* */
+#endif
+
+#define __RWSEM_INITIALIZER(name,count)					\
+	{ ATOMIC_INIT(count), 0,					\
+	  __WAIT_QUEUE_HEAD_INITIALIZER((name).wait),			\
+	  __WAIT_QUEUE_HEAD_INITIALIZER((name).write_bias_wait)		\
+	  __SEM_DEBUG_INIT(name) __RWSEM_DEBUG_INIT }
+
+#define __DECLARE_RWSEM_GENERIC(name,count) \
+	struct rw_semaphore name = __RWSEM_INITIALIZER(name,count)
+
+#define DECLARE_RWSEM(name) \
+	__DECLARE_RWSEM_GENERIC(name, RW_LOCK_BIAS)
+#define DECLARE_RWSEM_READ_LOCKED(name) \
+	__DECLARE_RWSEM_GENERIC(name, RW_LOCK_BIAS-1)
+#define DECLARE_RWSEM_WRITE_LOCKED(name) \
+	__DECLARE_RWSEM_GENERIC(name, 0)
+
+extern inline void init_rwsem(struct rw_semaphore *sem)
+{
+	atomic_set(&sem->count, RW_LOCK_BIAS);
+	sem->granted = 0;
+	init_waitqueue_head(&sem->wait);
+	init_waitqueue_head(&sem->write_bias_wait);
+#if WAITQUEUE_DEBUG
+	sem->__magic = (long)&sem->__magic;
+	atomic_set(&sem->readers, 0);
+	atomic_set(&sem->writers, 0);
+#endif
+}
+
+/* The expensive part is outlined.  */
+extern void __down_read(struct rw_semaphore *sem, int count);
+extern void __down_write(struct rw_semaphore *sem, int count);
+extern void __rwsem_wake(struct rw_semaphore *sem, unsigned long readers);
+
+extern inline void down_read(struct rw_semaphore *sem)
+{
+	int count;
+
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+
+	count = atomic_dec_return(&sem->count);
+	if (count < 0) {
+		__down_read(sem, count);
+	}
+	mb();
+
+#if WAITQUEUE_DEBUG
+	if (sem->granted & 2)
+		BUG();
+	if (atomic_read(&sem->writers))
+		BUG();
+	atomic_inc(&sem->readers);
+#endif
+}
+
+extern inline void down_write(struct rw_semaphore *sem)
+{
+	int count;
+
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+
+	count = atomic_sub_return(RW_LOCK_BIAS, &sem->count);
+	if (count) {
+		__down_write(sem, count);
+	}
+	mb();
+
+#if WAITQUEUE_DEBUG
+	if (atomic_read(&sem->writers))
+		BUG();
+	if (atomic_read(&sem->readers))
+		BUG();
+	if (sem->granted & 3)
+		BUG();
+	atomic_inc(&sem->writers);
+#endif
+}
+
+/* When a reader does a release, the only significant case is when
+   there was a writer waiting, and we've bumped the count to 0: we must
+   wake the writer up.  */
+
+extern inline void up_read(struct rw_semaphore *sem)
+{
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+	if (sem->granted & 2)
+		BUG();
+	if (atomic_read(&sem->writers))
+		BUG();
+	atomic_dec(&sem->readers);
+#endif
+
+	mb();
+	if (atomic_inc_return(&sem->count) == 0)
+		__rwsem_wake(sem, 0);
+}
+
+/*
+ * Releasing the writer is easy -- just release it and wake up any sleepers.
+ */
+extern inline void up_write(struct rw_semaphore *sem)
+{
+	int count;
+
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+	if (sem->granted & 3)
+		BUG();
+	if (atomic_read(&sem->readers))
+		BUG();
+	if (atomic_read(&sem->writers) != 1)
+		BUG();
+	atomic_dec(&sem->writers);
+#endif
+
+	mb();
+	count = atomic_add_return(RW_LOCK_BIAS, &sem->count);
+	if (count - RW_LOCK_BIAS < 0 && count >= 0) {
+		/* Only do the wake if we're no longer negative.  */
+		__rwsem_wake(sem, count);
+	}
+}
+
 #endif /* _ASM_SEMAPHORE_H */