drivers/gpu/drm/drm_lock.c - kernel/lockdown - Git at Google

 /**
  * \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 <linux/export.h>
 #include <drm/drmP.h>
 #include "drm_legacy.h"
 #include "drm_internal.h"

 static int drm_notifier(void *priv);

 static int drm_lock_take(struct drm_lock_data *lock_data, unsigned int context);

 /**
  * 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.
  */
 int drm_legacy_lock(struct drm_device *dev, void *data,
 		    struct drm_file *file_priv)
 {
 	DECLARE_WAITQUEUE(entry, current);
 	struct drm_lock *lock = data;
 	struct drm_master *master = file_priv->master;
 	int ret = 0;

 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EINVAL;

 	++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),
 		  master->lock.hw_lock->lock, lock->flags);

 	add_wait_queue(&master->lock.lock_queue, &entry);
 	spin_lock_bh(&master->lock.spinlock);
 	master->lock.user_waiters++;
 	spin_unlock_bh(&master->lock.spinlock);

 	for (;;) {
 		__set_current_state(TASK_INTERRUPTIBLE);
 		if (!master->lock.hw_lock) {
 			/* Device has been unregistered */
 			send_sig(SIGTERM, current, 0);
 			ret = -EINTR;
 			break;
 		}
 		if (drm_lock_take(&master->lock, lock->context)) {
 			master->lock.file_priv = file_priv;
 			master->lock.lock_time = jiffies;
 			break;	/* Got lock */
 		}

 		/* Contention */
 		mutex_unlock(&drm_global_mutex);
 		schedule();
 		mutex_lock(&drm_global_mutex);
 		if (signal_pending(current)) {
 			ret = -EINTR;
 			break;
 		}
 	}
 	spin_lock_bh(&master->lock.spinlock);
 	master->lock.user_waiters--;
 	spin_unlock_bh(&master->lock.spinlock);
 	__set_current_state(TASK_RUNNING);
 	remove_wait_queue(&master->lock.lock_queue, &entry);

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

 	/* don't set the block all signals on the master process for now
 	 * really probably not the correct answer but lets us debug xkb
  	 * xserver for now */
 	if (!file_priv->is_master) {
 		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 = master->lock.hw_lock;
 		block_all_signals(drm_notifier, dev, &dev->sigmask);
 	}

 	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;
 		}
 	}

 	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.
  */
 int drm_legacy_unlock(struct drm_device *dev, void *data, struct drm_file *file_priv)
 {
 	struct drm_lock *lock = data;
 	struct drm_master *master = file_priv->master;

 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EINVAL;

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

 	if (drm_legacy_lock_free(&master->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.
  */
 static
 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_bh(&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_bh(&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.
  */
 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.
  */
 int drm_legacy_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_bh(&lock_data->spinlock);
 	if (lock_data->kernel_waiters != 0) {
 		drm_lock_transfer(lock_data, 0);
 		lock_data->idle_has_lock = 1;
 		spin_unlock_bh(&lock_data->spinlock);
 		return 1;
 	}
 	spin_unlock_bh(&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_device structure.
  * \return one if the signal should be delivered normally, or zero if the
  * signal should be blocked.
  */
 static int drm_notifier(void *priv)
 {
 	struct drm_device *dev = priv;
 	struct drm_hw_lock *lock = dev->sigdata.lock;
 	unsigned int old, new, prev;

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

 	/* Otherwise, set flag to force call to
 	   drmUnlock */
 	do {
 		old = lock->lock;
 		new = old | _DRM_LOCK_CONT;
 		prev = cmpxchg(&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.
  */

 void drm_legacy_idlelock_take(struct drm_lock_data *lock_data)
 {
 	int ret;

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

 		spin_unlock_bh(&lock_data->spinlock);
 		ret = drm_lock_take(lock_data, DRM_KERNEL_CONTEXT);
 		spin_lock_bh(&lock_data->spinlock);

 		if (ret == 1)
 			lock_data->idle_has_lock = 1;
 	}
 	spin_unlock_bh(&lock_data->spinlock);
 }
 EXPORT_SYMBOL(drm_legacy_idlelock_take);

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

 	spin_lock_bh(&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_bh(&lock_data->spinlock);
 }
 EXPORT_SYMBOL(drm_legacy_idlelock_release);

 int drm_legacy_i_have_hw_lock(struct drm_device *dev,
 			      struct drm_file *file_priv)
 {
 	struct drm_master *master = file_priv->master;
 	return (file_priv->lock_count && master->lock.hw_lock &&
 		_DRM_LOCK_IS_HELD(master->lock.hw_lock->lock) &&
 		master->lock.file_priv == file_priv);
 }
	/**
	* \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 <linux/export.h>
	#include <drm/drmP.h>
	#include "drm_legacy.h"
	#include "drm_internal.h"

	static int drm_notifier(void *priv);

	static int drm_lock_take(struct drm_lock_data *lock_data, unsigned int context);

	/**
	* 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.
	*/
	int drm_legacy_lock(struct drm_device dev, void data,
	struct drm_file *file_priv)
	{
	DECLARE_WAITQUEUE(entry, current);
	struct drm_lock *lock = data;
	struct drm_master *master = file_priv->master;
	int ret = 0;

	if (drm_core_check_feature(dev, DRIVER_MODESET))
	return -EINVAL;

	++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),
	master->lock.hw_lock->lock, lock->flags);

	add_wait_queue(&master->lock.lock_queue, &entry);
	spin_lock_bh(&master->lock.spinlock);
	master->lock.user_waiters++;
	spin_unlock_bh(&master->lock.spinlock);

	for (;;) {
	__set_current_state(TASK_INTERRUPTIBLE);
	if (!master->lock.hw_lock) {
	/* Device has been unregistered */
	send_sig(SIGTERM, current, 0);
	ret = -EINTR;
	break;
	}
	if (drm_lock_take(&master->lock, lock->context)) {
	master->lock.file_priv = file_priv;
	master->lock.lock_time = jiffies;
	break; /* Got lock */
	}

	/* Contention */
	mutex_unlock(&drm_global_mutex);
	schedule();
	mutex_lock(&drm_global_mutex);
	if (signal_pending(current)) {
	ret = -EINTR;
	break;
	}
	}
	spin_lock_bh(&master->lock.spinlock);
	master->lock.user_waiters--;
	spin_unlock_bh(&master->lock.spinlock);
	__set_current_state(TASK_RUNNING);
	remove_wait_queue(&master->lock.lock_queue, &entry);

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

	/* don't set the block all signals on the master process for now
	* really probably not the correct answer but lets us debug xkb
	* xserver for now */
	if (!file_priv->is_master) {
	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 = master->lock.hw_lock;
	block_all_signals(drm_notifier, dev, &dev->sigmask);
	}

	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;
	}
	}

	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.
	*/
	int drm_legacy_unlock(struct drm_device dev, void data, struct drm_file *file_priv)
	{
	struct drm_lock *lock = data;
	struct drm_master *master = file_priv->master;

	if (drm_core_check_feature(dev, DRIVER_MODESET))
	return -EINVAL;

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

	if (drm_legacy_lock_free(&master->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.
	*/
	static
	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_bh(&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_bh(&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.
	*/
	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.
	*/
	int drm_legacy_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_bh(&lock_data->spinlock);
	if (lock_data->kernel_waiters != 0) {
	drm_lock_transfer(lock_data, 0);
	lock_data->idle_has_lock = 1;
	spin_unlock_bh(&lock_data->spinlock);
	return 1;
	}
	spin_unlock_bh(&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_device structure.
	* \return one if the signal should be delivered normally, or zero if the
	* signal should be blocked.
	*/
	static int drm_notifier(void *priv)
	{
	struct drm_device *dev = priv;
	struct drm_hw_lock *lock = dev->sigdata.lock;
	unsigned int old, new, prev;

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

	/* Otherwise, set flag to force call to
	drmUnlock */
	do {
	old = lock->lock;
	new = old \| _DRM_LOCK_CONT;
	prev = cmpxchg(&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.
	*/

	void drm_legacy_idlelock_take(struct drm_lock_data *lock_data)
	{
	int ret;

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

	spin_unlock_bh(&lock_data->spinlock);
	ret = drm_lock_take(lock_data, DRM_KERNEL_CONTEXT);
	spin_lock_bh(&lock_data->spinlock);

	if (ret == 1)
	lock_data->idle_has_lock = 1;
	}
	spin_unlock_bh(&lock_data->spinlock);
	}
	EXPORT_SYMBOL(drm_legacy_idlelock_take);

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

	spin_lock_bh(&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_bh(&lock_data->spinlock);
	}
	EXPORT_SYMBOL(drm_legacy_idlelock_release);

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