2 files changed, 187 insertions, 0 deletions

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
new file mode 100644
index 000000000000..6383d54bf983
--- /dev/null
+++ b/include/asm-generic/qrwlock.h
@@ -0,0 +1,166 @@
+/*
+ * 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     1               /* A writer is waiting     */
+#define _QW_LOCKED      0xff            /* A writer holds the lock */
+#define _QW_WMASK       0xff            /* Writer mask             */
+#define _QR_SHIFT       8               /* Reader count shift      */
+#define _QR_BIAS        (1U << _QR_SHIFT)
+
+/*
+ * External function declarations
+ */
+extern void queue_read_lock_slowpath(struct qrwlock *lock);
+extern void queue_write_lock_slowpath(struct qrwlock *lock);
+
+/**
+ * queue_read_can_lock- would read_trylock() succeed?
+ * @lock: Pointer to queue rwlock structure
+ */
+static inline int queue_read_can_lock(struct qrwlock *lock)
+{
+        return !(atomic_read(&lock->cnts) & _QW_WMASK);
+}
+
+/**
+ * queue_write_can_lock- would write_trylock() succeed?
+ * @lock: Pointer to queue rwlock structure
+ */
+static inline int queue_write_can_lock(struct qrwlock *lock)
+{
+        return !atomic_read(&lock->cnts);
+}
+
+/**
+ * queue_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 queue_read_trylock(struct qrwlock *lock)
+{
+        u32 cnts;
+
+        cnts = atomic_read(&lock->cnts);
+        if (likely(!(cnts & _QW_WMASK))) {
+                cnts = (u32)atomic_add_return(_QR_BIAS, &lock->cnts);
+                if (likely(!(cnts & _QW_WMASK)))
+                        return 1;
+                atomic_sub(_QR_BIAS, &lock->cnts);
+        }
+        return 0;
+}
+
+/**
+ * queue_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 queue_write_trylock(struct qrwlock *lock)
+{
+        u32 cnts;
+
+        cnts = atomic_read(&lock->cnts);
+        if (unlikely(cnts))
+                return 0;
+
+        return likely(atomic_cmpxchg(&lock->cnts,
+                                     cnts, cnts | _QW_LOCKED) == cnts);
+}
+/**
+ * queue_read_lock - acquire read lock of a queue rwlock
+ * @lock: Pointer to queue rwlock structure
+ */
+static inline void queue_read_lock(struct qrwlock *lock)
+{
+        u32 cnts;
+
+        cnts = atomic_add_return(_QR_BIAS, &lock->cnts);
+        if (likely(!(cnts & _QW_WMASK)))
+                return;
+
+        /* The slowpath will decrement the reader count, if necessary. */
+        queue_read_lock_slowpath(lock);
+}
+
+/**
+ * queue_write_lock - acquire write lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ */
+static inline void queue_write_lock(struct qrwlock *lock)
+{
+        /* Optimize for the unfair lock case where the fair flag is 0. */
+        if (atomic_cmpxchg(&lock->cnts, 0, _QW_LOCKED) == 0)
+                return;
+
+        queue_write_lock_slowpath(lock);
+}
+
+/**
+ * queue_read_unlock - release read lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ */
+static inline void queue_read_unlock(struct qrwlock *lock)
+{
+        /*
+         * Atomically decrement the reader count
+         */
+        smp_mb__before_atomic();
+        atomic_sub(_QR_BIAS, &lock->cnts);
+}
+
+#ifndef queue_write_unlock
+/**
+ * queue_write_unlock - release write lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ */
+static inline void queue_write_unlock(struct qrwlock *lock)
+{
+        /*
+         * If the writer field is atomic, it can be cleared directly.
+         * Otherwise, an atomic subtraction will be used to clear it.
+         */
+        smp_mb__before_atomic();
+        atomic_sub(_QW_LOCKED, &lock->cnts);
+}
+#endif
+
+/*
+ * Remapping rwlock architecture specific functions to the corresponding
+ * queue rwlock functions.
+ */
+#define arch_read_can_lock(l)   queue_read_can_lock(l)
+#define arch_write_can_lock(l)  queue_write_can_lock(l)
+#define arch_read_lock(l)       queue_read_lock(l)
+#define arch_write_lock(l)      queue_write_lock(l)
+#define arch_read_trylock(l)    queue_read_trylock(l)
+#define arch_write_trylock(l)   queue_write_trylock(l)
+#define arch_read_unlock(l)     queue_read_unlock(l)
+#define arch_write_unlock(l)    queue_write_unlock(l)
+
+#endif /* __ASM_GENERIC_QRWLOCK_H */
diff --git a/include/asm-generic/qrwlock_types.h b/include/asm-generic/qrwlock_types.h
new file mode 100644
index 000000000000..4d76f24df518
--- /dev/null
+++ b/include/asm-generic/qrwlock_types.h
@@ -0,0 +1,21 @@
+#ifndef __ASM_GENERIC_QRWLOCK_TYPES_H
+#define __ASM_GENERIC_QRWLOCK_TYPES_H
+
+#include <linux/types.h>
+#include <asm/spinlock_types.h>
+
+/*
+ * The queue read/write lock data structure
+ */
+
+typedef struct qrwlock {
+        atomic_t                cnts;
+        arch_spinlock_t         lock;
+} arch_rwlock_t;
+
+#define __ARCH_RW_LOCK_UNLOCKED {               \
+        .cnts = ATOMIC_INIT(0),                 \
+        .lock = __ARCH_SPIN_LOCK_UNLOCKED,      \
+}
+
+#endif /* __ASM_GENERIC_QRWLOCK_TYPES_H */