patch-2.4.19 linux-2.4.19/include/asm-s390/rwsem.h

• Lines: 210
• Date: Fri Aug 2 17:39:45 2002
• Orig file: linux-2.4.18/include/asm-s390/rwsem.h
• Orig date: Wed Dec 31 16:00:00 1969

diff -urN linux-2.4.18/include/asm-s390/rwsem.h linux-2.4.19/include/asm-s390/rwsem.h
@@ -0,0 +1,209 @@
+#ifndef _S390_RWSEM_H
+#define _S390_RWSEM_H
+
+/*
+ *  include/asm-s390/rwsem.h
+ *
+ *  S390 version
+ *    Copyright (C) 2002 IBM Deutschland Entwicklung GmbH, IBM Corporation
+ *    Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
+ *
+ *  Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
+ */
+
+/*
+ *
+ * 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. This can be determined because XADD returns the old value.
+ * 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).
+ *
+ * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
+ * be extended to 65534 by manually checking the whole MSW rather than relying
+ * on the S flag.
+ *
+ * The value of ACTIVE_BIAS supports up to 65535 active processes.
+ *
+ * This should be totally fair - if anything is waiting, a process that wants a
+ * lock will go to the back of the queue. When the currently active lock is
+ * released, if there's a writer at the front of the queue, then that and only
+ * that will be woken up; if there's a bunch of consequtive readers at the
+ * front, then they'll all be woken up, but no other readers will be.
+ */
+
+#ifndef _LINUX_RWSEM_H
+#error please dont include asm/rwsem.h directly, use linux/rwsem.h instead
+#endif
+
+#ifdef __KERNEL__
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+
+struct rwsem_waiter;
+
+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 *);
+
+/*
+ * the semaphore definition
+ */
+struct rw_semaphore {
+	signed long		count;
+	spinlock_t		wait_lock;
+	struct list_head	wait_list;
+};
+
+#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)
+
+/*
+ * initialisation
+ */
+#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)
+
+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)
+{
+	signed long old, new;
+
+	__asm__ __volatile__(
+		"   l    %0,0(%2)\n"
+		"0: lr   %1,%0\n"
+		"   ahi  %1,%3\n"
+		"   cs   %0,%1,0(%2)\n"
+		"   jl   0b"
+                : "=&d" (old), "=&d" (new)
+		: "a" (&sem->count), "i" (RWSEM_ACTIVE_READ_BIAS)
+		: "cc", "memory" );
+	if (old < 0)
+		rwsem_down_read_failed(sem);
+}
+
+/*
+ * lock for writing
+ */
+static inline void __down_write(struct rw_semaphore *sem)
+{
+	signed long old, new, tmp;
+
+	tmp = RWSEM_ACTIVE_WRITE_BIAS;
+	__asm__ __volatile__(
+		"   l    %0,0(%2)\n"
+		"0: lr   %1,%0\n"
+		"   a    %1,%3\n"
+		"   cs   %0,%1,0(%2)\n"
+		"   jl   0b"
+                : "=&d" (old), "=&d" (new)
+		: "a" (&sem->count), "m" (tmp)
+		: "cc", "memory" );
+	if (old != 0)
+		rwsem_down_write_failed(sem);
+}
+
+/*
+ * unlock after reading
+ */
+static inline void __up_read(struct rw_semaphore *sem)
+{
+	signed long old, new;
+
+	__asm__ __volatile__(
+		"   l    %0,0(%2)\n"
+		"0: lr   %1,%0\n"
+		"   ahi  %1,%3\n"
+		"   cs   %0,%1,0(%2)\n"
+		"   jl   0b"
+                : "=&d" (old), "=&d" (new)
+		: "a" (&sem->count), "i" (-RWSEM_ACTIVE_READ_BIAS)
+		: "cc", "memory" );
+	if (new < 0)
+		if ((new & RWSEM_ACTIVE_MASK) == 0)
+			rwsem_wake(sem);
+}
+
+/*
+ * unlock after writing
+ */
+static inline void __up_write(struct rw_semaphore *sem)
+{
+	signed long old, new, tmp;
+
+	tmp = -RWSEM_ACTIVE_WRITE_BIAS;
+	__asm__ __volatile__(
+		"   l    %0,0(%2)\n"
+		"0: lr   %1,%0\n"
+		"   a    %1,%3\n"
+		"   cs   %0,%1,0(%2)\n"
+		"   jl   0b"
+                : "=&d" (old), "=&d" (new)
+		: "a" (&sem->count), "m" (tmp)
+		: "cc", "memory" );
+	if (new < 0)
+		if ((new & RWSEM_ACTIVE_MASK) == 0)
+			rwsem_wake(sem);
+}
+
+/*
+ * implement atomic add functionality
+ */
+static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
+{
+	signed long old, new;
+
+	__asm__ __volatile__(
+		"   l    %0,0(%2)\n"
+		"0: lr   %1,%0\n"
+		"   ar   %1,%3\n"
+		"   cs   %0,%1,0(%2)\n"
+		"   jl   0b"
+                : "=&d" (old), "=&d" (new)
+		: "a" (&sem->count), "d" (delta)
+		: "cc", "memory" );
+}
+
+/*
+ * implement exchange and add functionality
+ */
+static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
+{
+	signed long old, new;
+
+	__asm__ __volatile__(
+		"   l    %0,0(%2)\n"
+		"0: lr   %1,%0\n"
+		"   ar   %1,%3\n"
+		"   cs   %0,%1,0(%2)\n"
+		"   jl   0b"
+                : "=&d" (old), "=&d" (new)
+		: "a" (&sem->count), "d" (delta)
+		: "cc", "memory" );
+	return new;
+}
+
+#endif /* __KERNEL__ */
+#endif /* _S390_RWSEM_H */