text: /*
   * arch/v850/kernel/semaphore.c -- Semaphore support
   *
   *  Copyright (C) 1998-2000  IBM Corporation
   *  Copyright (C) 1999  Linus Torvalds
   *
   * 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.
   *
   * This file is a copy of the s390 version, arch/s390/kernel/semaphore.c
   *    Author(s): Martin Schwidefsky
   * which was derived from the i386 version, linux/arch/i386/kernel/semaphore.c
   */
  
  #include <linux/errno.h>
  #include <linux/sched.h>
  
  #include <asm/semaphore.h>
  
  /*
   * Semaphores are implemented using a two-way counter:
   * The "count" variable is decremented for each process
   * that tries to acquire the semaphore, while the "sleeping"
   * variable is a count of such acquires.
   *
   * 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.
   *
   * "sleeping" and the contention routine ordering is
   * protected by the semaphore spinlock.
   *
   * 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.
   */
  
  /*
   * Logic:
   *  - only on a boundary condition do we need to care. When we go
   *    from a negative count to a non-negative, we wake people up.
   *  - when we go from a non-negative count to a negative do we
   *    (a) synchronize with the "sleeper" count and (b) make sure
   *    that we're on the wakeup list before we synchronize so that
   *    we cannot lose wakeup events.
   */
  
  void __up(struct semaphore *sem)
  {
  	wake_up(&sem->wait);
  }
  
  static spinlock_t semaphore_lock = SPIN_LOCK_UNLOCKED;
  
  void __down(struct semaphore * sem)
  {
  	struct task_struct *tsk = current;
  	DECLARE_WAITQUEUE(wait, tsk);
  	tsk->state = TASK_UNINTERRUPTIBLE;
  	add_wait_queue_exclusive(&sem->wait, &wait);
  
  	spin_lock_irq(&semaphore_lock);
  	sem->sleepers++;
  	for (;;) {
  		int sleepers = sem->sleepers;
  
  		/*
  		 * Add "everybody else" into it. They aren't
  		 * playing, because we own the spinlock.
  		 */
  		if (!atomic_add_negative(sleepers - 1, &sem->count)) {
  			sem->sleepers = 0;
  			break;
  		}
  		sem->sleepers = 1;	/* us - see -1 above */
  		spin_unlock_irq(&semaphore_lock);
  
  		schedule();
  		tsk->state = TASK_UNINTERRUPTIBLE;
  		spin_lock_irq(&semaphore_lock);
  	}
  	spin_unlock_irq(&semaphore_lock);
  	remove_wait_queue(&sem->wait, &wait);
  	tsk->state = TASK_RUNNING;
  	wake_up(&sem->wait);
  }
  
  int __down_interruptible(struct semaphore * sem)
  {
  	int retval = 0;
  	struct task_struct *tsk = current;
  	DECLARE_WAITQUEUE(wait, tsk);
  	tsk->state = TASK_INTERRUPTIBLE;
  	add_wait_queue_exclusive(&sem->wait, &wait);
  
  	spin_lock_irq(&semaphore_lock);
  	sem->sleepers ++;
  	for (;;) {
  		int sleepers = sem->sleepers;
  
  		/*
  		 * With signals pending, this turns into
  		 * the trylock failure case - we won't be
  		 * sleeping, and we* can't get the lock as
  		 * it has contention. Just correct the count
  		 * and exit.
  		 */
  		if (signal_pending(current)) {
  			retval = -EINTR;
  			sem->sleepers = 0;
  			atomic_add(sleepers, &sem->count);
  			break;
  		}
  
  		/*
  		 * Add "everybody else" into it. They aren't
  		 * playing, because we own the spinlock. The
  		 * "-1" is because we're still hoping to get
  		 * the lock.
  		 */
  		if (!atomic_add_negative(sleepers - 1, &sem->count)) {
  			sem->sleepers = 0;
  			break;
  		}
  		sem->sleepers = 1;	/* us - see -1 above */
  		spin_unlock_irq(&semaphore_lock);
  
  		schedule();
  		tsk->state = TASK_INTERRUPTIBLE;
  		spin_lock_irq(&semaphore_lock);
  	}
  	spin_unlock_irq(&semaphore_lock);
  	tsk->state = TASK_RUNNING;
  	remove_wait_queue(&sem->wait, &wait);
  	wake_up(&sem->wait);
  	return retval;
  }
  
  /*
   * Trylock failed - make sure we correct for
   * having decremented the count.
   */
  int __down_trylock(struct semaphore * sem)
  {
          unsigned long flags;
  	int sleepers;
  
  	spin_lock_irqsave(&semaphore_lock, flags);
  	sleepers = sem->sleepers + 1;
  	sem->sleepers = 0;
  
  	/*
  	 * Add "everybody else" and us into it. They aren't
  	 * playing, because we own the spinlock.
  	 */
  	if (!atomic_add_negative(sleepers, &sem->count))
  		wake_up(&sem->wait);
  
  	spin_unlock_irqrestore(&semaphore_lock, flags);
  	return 1;
  }
  