1 files changed, 138 insertions, 0 deletions
diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
new file mode 100644
index 000000000..0f7062bd5
--- /dev/null
+++ b/include/asm-generic/qrwlock.h
@@ -0,0 +1,138 @@
+/*
+ * Queue read/write lock
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
+ *
+ * Authors: Waiman Long <waiman.long@hp.com>
+ */
+#ifndef __ASM_GENERIC_QRWLOCK_H
+#define __ASM_GENERIC_QRWLOCK_H
+
+#include <linux/atomic.h>
+#include <asm/barrier.h>
+#include <asm/processor.h>
+
+#include <asm-generic/qrwlock_types.h>
+
+/*
+ * Writer states & reader shift and bias.
+ */
+#define	_QW_WAITING	0x100		/* A writer is waiting	   */
+#define	_QW_LOCKED	0x0ff		/* A writer holds the lock */
+#define	_QW_WMASK	0x1ff		/* Writer mask		   */
+#define	_QR_SHIFT	9		/* Reader count shift	   */
+#define _QR_BIAS	(1U << _QR_SHIFT)
+
+/*
+ * External function declarations
+ */
+extern void queued_read_lock_slowpath(struct qrwlock *lock);
+extern void queued_write_lock_slowpath(struct qrwlock *lock);
+
+/**
+ * queued_read_trylock - try to acquire read lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ * Return: 1 if lock acquired, 0 if failed
+ */
+static inline int queued_read_trylock(struct qrwlock *lock)
+{
+	u32 cnts;
+
+	cnts = atomic_read(&lock->cnts);
+	if (likely(!(cnts & _QW_WMASK))) {
+		cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
+		if (likely(!(cnts & _QW_WMASK)))
+			return 1;
+		atomic_sub(_QR_BIAS, &lock->cnts);
+	}
+	return 0;
+}
+
+/**
+ * queued_write_trylock - try to acquire write lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ * Return: 1 if lock acquired, 0 if failed
+ */
+static inline int queued_write_trylock(struct qrwlock *lock)
+{
+	u32 cnts;
+
+	cnts = atomic_read(&lock->cnts);
+	if (unlikely(cnts))
+		return 0;
+
+	return likely(atomic_cmpxchg_acquire(&lock->cnts,
+					     cnts, cnts | _QW_LOCKED) == cnts);
+}
+/**
+ * queued_read_lock - acquire read lock of a queue rwlock
+ * @lock: Pointer to queue rwlock structure
+ */
+static inline void queued_read_lock(struct qrwlock *lock)
+{
+	u32 cnts;
+
+	cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
+	if (likely(!(cnts & _QW_WMASK)))
+		return;
+
+	/* The slowpath will decrement the reader count, if necessary. */
+	queued_read_lock_slowpath(lock);
+}
+
+/**
+ * queued_write_lock - acquire write lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ */
+static inline void queued_write_lock(struct qrwlock *lock)
+{
+	/* Optimize for the unfair lock case where the fair flag is 0. */
+	if (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0)
+		return;
+
+	queued_write_lock_slowpath(lock);
+}
+
+/**
+ * queued_read_unlock - release read lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ */
+static inline void queued_read_unlock(struct qrwlock *lock)
+{
+	/*
+	 * Atomically decrement the reader count
+	 */
+	(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
+}
+
+/**
+ * queued_write_unlock - release write lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ */
+static inline void queued_write_unlock(struct qrwlock *lock)
+{
+	smp_store_release(&lock->wlocked, 0);
+}
+
+/*
+ * Remapping rwlock architecture specific functions to the corresponding
+ * queue rwlock functions.
+ */
+#define arch_read_lock(l)	queued_read_lock(l)
+#define arch_write_lock(l)	queued_write_lock(l)
+#define arch_read_trylock(l)	queued_read_trylock(l)
+#define arch_write_trylock(l)	queued_write_trylock(l)
+#define arch_read_unlock(l)	queued_read_unlock(l)
+#define arch_write_unlock(l)	queued_write_unlock(l)
+
+#endif /* __ASM_GENERIC_QRWLOCK_H */