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drm_lock.c

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/**
 * \file drm_lock.c
 * IOCTLs for locking
 *
 * \author Rickard E. (Rik) Faith <faith@valinux.com>
 * \author Gareth Hughes <gareth@valinux.com>
 */

/*
 * Created: Tue Feb  2 08:37:54 1999 by faith@valinux.com
 *
 * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
 * Copyright 2000 VA Linux Systems, Inc., Sunnyvale, California.
 * All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * VA LINUX SYSTEMS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

#include "drmP.h"

static int drm_notifier(void *priv);

/**
 * Lock ioctl.
 *
 * \param inode device inode.
 * \param file_priv DRM file private.
 * \param cmd command.
 * \param arg user argument, pointing to a drm_lock structure.
 * \return zero on success or negative number on failure.
 *
 * Add the current task to the lock wait queue, and attempt to take to lock.
 */
00051 int drm_lock(struct drm_device *dev, void *data, struct drm_file *file_priv)
{
      DECLARE_WAITQUEUE(entry, current);
      struct drm_lock *lock = data;
      int ret = 0;

      ++file_priv->lock_count;

      if (lock->context == DRM_KERNEL_CONTEXT) {
            DRM_ERROR("Process %d using kernel context %d\n",
                    task_pid_nr(current), lock->context);
            return -EINVAL;
      }

      DRM_DEBUG("%d (pid %d) requests lock (0x%08x), flags = 0x%08x\n",
              lock->context, task_pid_nr(current),
              dev->lock.hw_lock->lock, lock->flags);

      if (drm_core_check_feature(dev, DRIVER_DMA_QUEUE))
            if (lock->context < 0)
                  return -EINVAL;

      add_wait_queue(&dev->lock.lock_queue, &entry);
      spin_lock(&dev->lock.spinlock);
      dev->lock.user_waiters++;
      spin_unlock(&dev->lock.spinlock);
      for (;;) {
            __set_current_state(TASK_INTERRUPTIBLE);
            if (!dev->lock.hw_lock) {
                  /* Device has been unregistered */
                  ret = -EINTR;
                  break;
            }
            if (drm_lock_take(&dev->lock, lock->context)) {
                  dev->lock.file_priv = file_priv;
                  dev->lock.lock_time = jiffies;
                  atomic_inc(&dev->counts[_DRM_STAT_LOCKS]);
                  break;      /* Got lock */
            }

            /* Contention */
            schedule();
            if (signal_pending(current)) {
                  ret = -ERESTARTSYS;
                  break;
            }
      }
      spin_lock(&dev->lock.spinlock);
      dev->lock.user_waiters--;
      spin_unlock(&dev->lock.spinlock);
      __set_current_state(TASK_RUNNING);
      remove_wait_queue(&dev->lock.lock_queue, &entry);

      DRM_DEBUG("%d %s\n", lock->context,
              ret ? "interrupted" : "has lock");
      if (ret) return ret;

      sigemptyset(&dev->sigmask);
      sigaddset(&dev->sigmask, SIGSTOP);
      sigaddset(&dev->sigmask, SIGTSTP);
      sigaddset(&dev->sigmask, SIGTTIN);
      sigaddset(&dev->sigmask, SIGTTOU);
      dev->sigdata.context = lock->context;
      dev->sigdata.lock = dev->lock.hw_lock;
      block_all_signals(drm_notifier, &dev->sigdata, &dev->sigmask);

      if (dev->driver->dma_ready && (lock->flags & _DRM_LOCK_READY))
            dev->driver->dma_ready(dev);

      if (dev->driver->dma_quiescent && (lock->flags & _DRM_LOCK_QUIESCENT))
      {
            if (dev->driver->dma_quiescent(dev)) {
                  DRM_DEBUG("%d waiting for DMA quiescent\n",
                          lock->context);
                  return -EBUSY;
            }
      }

      if (dev->driver->kernel_context_switch &&
          dev->last_context != lock->context) {
            dev->driver->kernel_context_switch(dev, dev->last_context,
                                       lock->context);
      }

      return 0;
}

/**
 * Unlock ioctl.
 *
 * \param inode device inode.
 * \param file_priv DRM file private.
 * \param cmd command.
 * \param arg user argument, pointing to a drm_lock structure.
 * \return zero on success or negative number on failure.
 *
 * Transfer and free the lock.
 */
00149 int drm_unlock(struct drm_device *dev, void *data, struct drm_file *file_priv)
{
      struct drm_lock *lock = data;
      unsigned long irqflags;

      if (lock->context == DRM_KERNEL_CONTEXT) {
            DRM_ERROR("Process %d using kernel context %d\n",
                    task_pid_nr(current), lock->context);
            return -EINVAL;
      }

      spin_lock_irqsave(&dev->tasklet_lock, irqflags);

      if (dev->locked_tasklet_func) {
            dev->locked_tasklet_func(dev);

            dev->locked_tasklet_func = NULL;
      }

      spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);

      atomic_inc(&dev->counts[_DRM_STAT_UNLOCKS]);

      /* kernel_context_switch isn't used by any of the x86 drm
       * modules but is required by the Sparc driver.
       */
      if (dev->driver->kernel_context_switch_unlock)
            dev->driver->kernel_context_switch_unlock(dev);
      else {
            if (drm_lock_free(&dev->lock,lock->context)) {
                  /* FIXME: Should really bail out here. */
            }
      }

      unblock_all_signals();
      return 0;
}

/**
 * Take the heavyweight lock.
 *
 * \param lock lock pointer.
 * \param context locking context.
 * \return one if the lock is held, or zero otherwise.
 *
 * Attempt to mark the lock as held by the given context, via the \p cmpxchg instruction.
 */
00196 int drm_lock_take(struct drm_lock_data *lock_data,
              unsigned int context)
{
      unsigned int old, new, prev;
      volatile unsigned int *lock = &lock_data->hw_lock->lock;

      spin_lock(&lock_data->spinlock);
      do {
            old = *lock;
            if (old & _DRM_LOCK_HELD)
                  new = old | _DRM_LOCK_CONT;
            else {
                  new = context | _DRM_LOCK_HELD |
                        ((lock_data->user_waiters + lock_data->kernel_waiters > 1) ?
                         _DRM_LOCK_CONT : 0);
            }
            prev = cmpxchg(lock, old, new);
      } while (prev != old);
      spin_unlock(&lock_data->spinlock);

      if (_DRM_LOCKING_CONTEXT(old) == context) {
            if (old & _DRM_LOCK_HELD) {
                  if (context != DRM_KERNEL_CONTEXT) {
                        DRM_ERROR("%d holds heavyweight lock\n",
                                context);
                  }
                  return 0;
            }
      }

      if ((_DRM_LOCKING_CONTEXT(new)) == context && (new & _DRM_LOCK_HELD)) {
            /* Have lock */
            return 1;
      }
      return 0;
}

/**
 * This takes a lock forcibly and hands it to context.      Should ONLY be used
 * inside *_unlock to give lock to kernel before calling *_dma_schedule.
 *
 * \param dev DRM device.
 * \param lock lock pointer.
 * \param context locking context.
 * \return always one.
 *
 * Resets the lock file pointer.
 * Marks the lock as held by the given context, via the \p cmpxchg instruction.
 */
00245 static int drm_lock_transfer(struct drm_lock_data *lock_data,
                       unsigned int context)
{
      unsigned int old, new, prev;
      volatile unsigned int *lock = &lock_data->hw_lock->lock;

      lock_data->file_priv = NULL;
      do {
            old = *lock;
            new = context | _DRM_LOCK_HELD;
            prev = cmpxchg(lock, old, new);
      } while (prev != old);
      return 1;
}

/**
 * Free lock.
 *
 * \param dev DRM device.
 * \param lock lock.
 * \param context context.
 *
 * Resets the lock file pointer.
 * Marks the lock as not held, via the \p cmpxchg instruction. Wakes any task
 * waiting on the lock queue.
 */
00271 int drm_lock_free(struct drm_lock_data *lock_data, unsigned int context)
{
      unsigned int old, new, prev;
      volatile unsigned int *lock = &lock_data->hw_lock->lock;

      spin_lock(&lock_data->spinlock);
      if (lock_data->kernel_waiters != 0) {
            drm_lock_transfer(lock_data, 0);
            lock_data->idle_has_lock = 1;
            spin_unlock(&lock_data->spinlock);
            return 1;
      }
      spin_unlock(&lock_data->spinlock);

      do {
            old = *lock;
            new = _DRM_LOCKING_CONTEXT(old);
            prev = cmpxchg(lock, old, new);
      } while (prev != old);

      if (_DRM_LOCK_IS_HELD(old) && _DRM_LOCKING_CONTEXT(old) != context) {
            DRM_ERROR("%d freed heavyweight lock held by %d\n",
                    context, _DRM_LOCKING_CONTEXT(old));
            return 1;
      }
      wake_up_interruptible(&lock_data->lock_queue);
      return 0;
}

/**
 * If we get here, it means that the process has called DRM_IOCTL_LOCK
 * without calling DRM_IOCTL_UNLOCK.
 *
 * If the lock is not held, then let the signal proceed as usual.  If the lock
 * is held, then set the contended flag and keep the signal blocked.
 *
 * \param priv pointer to a drm_sigdata structure.
 * \return one if the signal should be delivered normally, or zero if the
 * signal should be blocked.
 */
00311 static int drm_notifier(void *priv)
{
      struct drm_sigdata *s = (struct drm_sigdata *) priv;
      unsigned int old, new, prev;

      /* Allow signal delivery if lock isn't held */
      if (!s->lock || !_DRM_LOCK_IS_HELD(s->lock->lock)
          || _DRM_LOCKING_CONTEXT(s->lock->lock) != s->context)
            return 1;

      /* Otherwise, set flag to force call to
         drmUnlock */
      do {
            old = s->lock->lock;
            new = old | _DRM_LOCK_CONT;
            prev = cmpxchg(&s->lock->lock, old, new);
      } while (prev != old);
      return 0;
}

/**
 * This function returns immediately and takes the hw lock
 * with the kernel context if it is free, otherwise it gets the highest priority when and if
 * it is eventually released.
 *
 * This guarantees that the kernel will _eventually_ have the lock _unless_ it is held
 * by a blocked process. (In the latter case an explicit wait for the hardware lock would cause
 * a deadlock, which is why the "idlelock" was invented).
 *
 * This should be sufficient to wait for GPU idle without
 * having to worry about starvation.
 */

00344 void drm_idlelock_take(struct drm_lock_data *lock_data)
{
      int ret = 0;

      spin_lock(&lock_data->spinlock);
      lock_data->kernel_waiters++;
      if (!lock_data->idle_has_lock) {

            spin_unlock(&lock_data->spinlock);
            ret = drm_lock_take(lock_data, DRM_KERNEL_CONTEXT);
            spin_lock(&lock_data->spinlock);

            if (ret == 1)
                  lock_data->idle_has_lock = 1;
      }
      spin_unlock(&lock_data->spinlock);
}
EXPORT_SYMBOL(drm_idlelock_take);

void drm_idlelock_release(struct drm_lock_data *lock_data)
{
      unsigned int old, prev;
      volatile unsigned int *lock = &lock_data->hw_lock->lock;

      spin_lock(&lock_data->spinlock);
      if (--lock_data->kernel_waiters == 0) {
            if (lock_data->idle_has_lock) {
                  do {
                        old = *lock;
                        prev = cmpxchg(lock, old, DRM_KERNEL_CONTEXT);
                  } while (prev != old);
                  wake_up_interruptible(&lock_data->lock_queue);
                  lock_data->idle_has_lock = 0;
            }
      }
      spin_unlock(&lock_data->spinlock);
}
EXPORT_SYMBOL(drm_idlelock_release);


int drm_i_have_hw_lock(struct drm_device *dev, struct drm_file *file_priv)
{
      return (file_priv->lock_count && dev->lock.hw_lock &&
            _DRM_LOCK_IS_HELD(dev->lock.hw_lock->lock) &&
            dev->lock.file_priv == file_priv);
}

EXPORT_SYMBOL(drm_i_have_hw_lock);

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