Date:	Thu, 24 Jan 2008 16:03:30 +0100
From:	monstr@...str.eu
To:	monstr@...str.eu
Cc:	linux-kernel@...r.kernel.org, stephen.neuendorffer@...inx.com,
	john.williams@...alogix.com, microblaze-uclinux@...e.uq.edu.au
Subject: [PATCH 05/52] [microblaze] Support for semaphores

From: Michal Simek <monstr@...str.eu>


Signed-off-by: Michal Simek <monstr@...str.eu>
---
 arch/microblaze/kernel/semaphore.c |  222 ++++++++++++++++++++++++++++++++++++
 include/asm-microblaze/semaphore.h |  100 ++++++++++++++++
 2 files changed, 322 insertions(+), 0 deletions(-)
 create mode 100644 arch/microblaze/kernel/semaphore.c
 create mode 100644 include/asm-microblaze/semaphore.h

diff --git a/arch/microblaze/kernel/semaphore.c b/arch/microblaze/kernel/semaphore.c
new file mode 100644
index 0000000..360fc7b
--- /dev/null
+++ b/arch/microblaze/kernel/semaphore.c
@@ -0,0 +1,222 @@
+/*
+ * arch/microblaze/kernel/semaphore.c
+ *
+ * Generic semaphore code. Buyer beware. Do your own specific changes
+ * in <asm/semaphore-helper.h>
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2001 - 2005 Tensilica Inc.
+ *
+ * Joe Taylor	<joe@...silica.com, joetylr@...oo.com>
+ * Chris Zankel	<chris@...kel.net>
+ * Marc Gauthier<marc@...silica.com, marc@...mni.uwaterloo.ca>
+ * Kevin Chea
+ */
+
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/init.h>
+#include <asm/semaphore.h>
+#include <asm/errno.h>
+
+/*
+ * These two _must_ execute atomically wrt each other.
+ */
+
+static inline void wake_one_more(struct semaphore *sem)
+{
+	atomic_inc((atomic_t *)&sem->sleepers);
+}
+
+static inline int waking_non_zero(struct semaphore *sem)
+{
+	unsigned long flags;
+	int ret = 0;
+
+	spin_lock_irqsave(&semaphore_wake_lock, flags);
+	if (sem->sleepers > 0) {
+		sem->sleepers--;
+		ret = 1;
+	}
+	spin_unlock_irqrestore(&semaphore_wake_lock, flags);
+	return ret;
+}
+
+/*
+ * waking_non_zero_interruptible:
+ *	1	got the lock
+ *	0	go to sleep
+ *	-EINTR	interrupted
+ *
+ * We must undo the sem->count down_interruptible() increment while we are
+ * protected by the spinlock in order to make atomic this atomic_inc() with the
+ * atomic_read() in wake_one_more(), otherwise we can race. -arca
+ */
+
+static inline int waking_non_zero_interruptible(struct semaphore *sem,
+						struct task_struct *tsk) {
+	unsigned long flags;
+	int ret = 0;
+
+	spin_lock_irqsave(&semaphore_wake_lock, flags);
+	if (sem->sleepers > 0) {
+		sem->sleepers--;
+		ret = 1;
+	} else if (signal_pending(tsk)) {
+		atomic_inc(&sem->count);
+		ret = -EINTR;
+	}
+	spin_unlock_irqrestore(&semaphore_wake_lock, flags);
+	return ret;
+}
+
+/*
+ * waking_non_zero_trylock:
+ *	1	failed to lock
+ *	0	got the lock
+ *
+ * We must undo the sem->count down_trylock() increment while we are
+ * protected by the spinlock in order to make atomic this atomic_inc() with the
+ * atomic_read() in wake_one_more(), otherwise we can race. -arca
+ */
+
+static inline int waking_non_zero_trylock(struct semaphore *sem)
+{
+	unsigned long flags;
+	int ret = 1;
+
+	spin_lock_irqsave(&semaphore_wake_lock, flags);
+	if (sem->sleepers <= 0)
+		atomic_inc(&sem->count);
+	else {
+		sem->sleepers--;
+		ret = 0;
+	}
+	spin_unlock_irqrestore(&semaphore_wake_lock, flags);
+	return ret;
+}
+
+spinlock_t semaphore_wake_lock;
+
+/*
+ * Semaphores are implemented using a two-way counter:
+ * The "count" variable is decremented for each process
+ * that tries to sleep, while the "waking" variable is
+ * incremented when the "up()" code goes to wake up waiting
+ * processes.
+ *
+ * Notably, the inline "up()" and "down()" functions can
+ * efficiently test if they need to do any extra work (up
+ * needs to do something only if count was negative before
+ * the increment operation.
+ *
+ * waking_non_zero() (from asm/semaphore.h) must execute
+ * atomically.
+ *
+ * When __up() is called, the count was negative before
+ * incrementing it, and we need to wake up somebody.
+ *
+ * This routine adds one to the count of processes that need to
+ * wake up and exit. ALL waiting processes actually wake up but
+ * only the one that gets to the "waking" field first will gate
+ * through and acquire the semaphore. The others will go back
+ * to sleep.
+ *
+ * Note that these functions are only called when there is
+ * contention on the lock, and as such all this is the
+ * "non-critical" part of the whole semaphore business. The
+ * critical part is the inline stuff in <asm/semaphore.h>
+ * where we want to avoid any extra jumps and calls.
+ */
+
+void __up(struct semaphore *sem)
+{
+	wake_one_more(sem);
+	wake_up(&sem->wait);
+}
+
+/*
+ * Perform the "down" function. Return zero for semaphore acquired,
+ * return negative for signalled out of the function.
+ *
+ * If called from __down, the return is ignored and the wait loop is
+ * not interruptible. This means that a task waiting on a semaphore
+ * using "down()" cannot be killed until someone does an "up()" on
+ * the semaphore.
+ *
+ * If called from __down_interruptible, the return value gets checked
+ * upon return. If the return value is negative then the task continues
+ * with the negative value in the return register (it can be tested by
+ * the caller).
+ *
+ * Either form may be used in conjunction with "up()".
+ *
+ */
+
+#define DOWN_VAR				\
+	struct task_struct *tsk = current;	\
+	wait_queue_t wait;			\
+	init_waitqueue_entry(&wait, tsk);
+
+#define DOWN_HEAD(task_state)						\
+									\
+									\
+	tsk->state = (task_state);					\
+	add_wait_queue(&sem->wait, &wait);				\
+									\
+	/*								\
+	 * Ok, we're set up. sem->count is known to be less than zero	\
+	 * so we must wait.						\
+	 *								\
+	 * We can let go the lock for purposes of waiting.		\
+	 * We re-acquire it after awaking so as to protect		\
+	 * all semaphore operations.					\
+	 *								\
+	 * If "up()" is called before we call waking_non_zero() then	\
+	 * we will catch it right away. If it is called later then	\
+	 * we will have to go through a wakeup cycle to catch it.	\
+	 *								\
+	 * Multiple waiters contend for the semaphore lock to see	\
+	 * who gets to gate through and who has to wait some more.	\
+	 */								\
+	for (;;) {
+
+#define DOWN_TAIL(task_state)			\
+		tsk->state = (task_state);	\
+	}					\
+	tsk->state = TASK_RUNNING;		\
+	remove_wait_queue(&sem->wait, &wait);
+
+void __sched __down(struct semaphore *sem) {
+	DOWN_VAR
+	DOWN_HEAD(TASK_UNINTERRUPTIBLE)
+	if (waking_non_zero(sem))
+		break;
+	schedule();
+	DOWN_TAIL(TASK_UNINTERRUPTIBLE)
+}
+
+int __sched __down_interruptible(struct semaphore *sem) {
+	int ret = 0;
+	DOWN_VAR
+	DOWN_HEAD(TASK_INTERRUPTIBLE)
+
+	ret = waking_non_zero_interruptible(sem, tsk);
+	if (ret) {
+		if (ret == 1)
+			/* ret != 0 only if we get interrupted -arca */
+			ret = 0;
+		break;
+	}
+	schedule();
+	DOWN_TAIL(TASK_INTERRUPTIBLE)
+	return ret;
+}
+
+int __down_trylock(struct semaphore *sem)
+{
+	return waking_non_zero_trylock(sem);
+}
diff --git a/include/asm-microblaze/semaphore.h b/include/asm-microblaze/semaphore.h
new file mode 100644
index 0000000..f59aae6
--- /dev/null
+++ b/include/asm-microblaze/semaphore.h
@@ -0,0 +1,100 @@
+/*
+ * include/asm-microblaze/semaphore.h
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2006 Atmark Techno, Inc.
+ */
+
+#ifndef _ASM_SEMAPHORE_H
+#define _ASM_SEMAPHORE_H
+
+#include <asm/atomic.h>
+#include <asm/system.h>
+#include <linux/wait.h>
+#include <linux/rwsem.h>
+
+struct semaphore {
+	atomic_t count;
+	int sleepers;
+	wait_queue_head_t wait;
+};
+
+#define __SEMAPHORE_INITIALIZER(name,n)					\
+{									\
+	.count		= ATOMIC_INIT(n),				\
+	.sleepers	= 0,						\
+	.wait		= __WAIT_QUEUE_HEAD_INITIALIZER((name).wait)	\
+}
+
+#define __DECLARE_SEMAPHORE_GENERIC(name,count)				\
+	struct semaphore name = __SEMAPHORE_INITIALIZER(name, count)
+
+#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name, 1)
+#define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name, 0)
+
+static inline void sema_init(struct semaphore *sem, int val)
+{
+	atomic_set(&sem->count, val);
+	sem->sleepers = 0;
+	init_waitqueue_head(&sem->wait);
+}
+
+static inline void init_MUTEX(struct semaphore *sem)
+{
+	sema_init(sem, 1);
+}
+
+static inline void init_MUTEX_LOCKED(struct semaphore *sem)
+{
+	sema_init(sem, 0);
+}
+
+asmlinkage void __down(struct semaphore *sem);
+asmlinkage int __down_interruptible(struct semaphore *sem);
+asmlinkage int __down_trylock(struct semaphore *sem);
+asmlinkage void __up(struct semaphore *sem);
+
+extern spinlock_t semaphore_wake_lock;
+
+static inline void down(struct semaphore *sem)
+{
+	might_sleep();
+
+	if (atomic_sub_return(1, &sem->count) < 0)
+		__down(sem);
+}
+
+static inline int down_interruptible(struct semaphore *sem)
+{
+	int ret = 0;
+
+	might_sleep();
+
+	if (atomic_sub_return(1, &sem->count) < 0)
+		ret = __down_interruptible(sem);
+	return ret;
+}
+
+static inline int down_trylock(struct semaphore *sem)
+{
+	int ret = 0;
+
+	if (atomic_sub_return(1, &sem->count) < 0)
+		ret = __down_trylock(sem);
+	return ret;
+}
+
+/*
+ * Note! This is subtle. We jump to wake people up only if
+ * the semaphore was negative (== somebody was waiting on it).
+ */
+static inline void up(struct semaphore *sem)
+{
+	if (atomic_add_return(1, &sem->count) <= 0)
+		__up(sem);
+}
+
+#endif /* _ASM_SEMAPHORE_H */
-- 
1.5.4.rc4.14.g6fc74

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