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/**************************************************************************
*
* Copyright (c) 2007 Tungsten Graphics, Inc., Cedar Park, TX., USA
* 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, sub license, 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 NON-INFRINGEMENT. IN NO EVENT SHALL
* THE COPYRIGHT HOLDERS, AUTHORS 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.
*
**************************************************************************/
/*
* Authors: Thomas Hellström <thomas-at-tungstengraphics-dot-com>
*/
/*
* This file implements a simple replacement for the buffer manager use
* of the heavyweight hardware lock.
* The lock is a read-write lock. Taking it in read mode is fast, and
* intended for in-kernel use only.
* Taking it in write mode is slow.
*
* The write mode is used only when there is a need to block all
* user-space processes from allocating a
* new memory area.
* Typical use in write mode is X server VT switching, and it's allowed
* to leave kernel space with the write lock held. If a user-space process
* dies while having the write-lock, it will be released during the file
* descriptor release.
*
* The read lock is typically placed at the start of an IOCTL- or
* user-space callable function that may end up allocating a memory area.
* This includes setstatus, super-ioctls and no_pfn; the latter may move
* unmappable regions to mappable. It's a bug to leave kernel space with the
* read lock held.
*
* Both read- and write lock taking is interruptible for low signal-delivery
* latency. The locking functions will return -EAGAIN if interrupted by a
* signal.
*
* Locking order: The lock should be taken BEFORE any kernel mutexes
* or spinlocks.
*/
#include "drmP.h"
void drm_bo_init_lock(struct drm_bo_lock *lock)
{
DRM_INIT_WAITQUEUE(&lock->queue);
atomic_set(&lock->write_lock_pending, 0);
atomic_set(&lock->readers, 0);
}
void drm_bo_read_unlock(struct drm_bo_lock *lock)
{
if (unlikely(atomic_add_negative(-1, &lock->readers)))
BUG();
if (atomic_read(&lock->readers) == 0)
wake_up_interruptible(&lock->queue);
}
EXPORT_SYMBOL(drm_bo_read_unlock);
int drm_bo_read_lock(struct drm_bo_lock *lock)
{
while (unlikely(atomic_read(&lock->write_lock_pending) != 0)) {
int ret;
ret = wait_event_interruptible
(lock->queue, atomic_read(&lock->write_lock_pending) == 0);
if (ret)
return -EAGAIN;
}
while (unlikely(!atomic_add_unless(&lock->readers, 1, -1))) {
int ret;
ret = wait_event_interruptible
(lock->queue, atomic_add_unless(&lock->readers, 1, -1));
if (ret)
return -EAGAIN;
}
return 0;
}
EXPORT_SYMBOL(drm_bo_read_lock);
static int __drm_bo_write_unlock(struct drm_bo_lock *lock)
{
if (unlikely(atomic_cmpxchg(&lock->readers, -1, 0) != -1))
return -EINVAL;
if (unlikely(atomic_cmpxchg(&lock->write_lock_pending, 1, 0) != 1))
return -EINVAL;
wake_up_interruptible(&lock->queue);
return 0;
}
static void drm_bo_write_lock_remove(struct drm_file *file_priv,
struct drm_user_object *item)
{
struct drm_bo_lock *lock = container_of(item, struct drm_bo_lock, base);
int ret;
ret = __drm_bo_write_unlock(lock);
BUG_ON(ret);
}
int drm_bo_write_lock(struct drm_bo_lock *lock, struct drm_file *file_priv)
{
int ret = 0;
struct drm_device *dev;
if (unlikely(atomic_cmpxchg(&lock->write_lock_pending, 0, 1) != 0))
return -EINVAL;
while (unlikely(atomic_cmpxchg(&lock->readers, 0, -1) != 0)) {
ret = wait_event_interruptible
(lock->queue, atomic_cmpxchg(&lock->readers, 0, -1) == 0);
if (ret) {
atomic_set(&lock->write_lock_pending, 0);
wake_up_interruptible(&lock->queue);
return -EAGAIN;
}
}
/*
* Add a dummy user-object, the destructor of which will
* make sure the lock is released if the client dies
* while holding it.
*/
dev = file_priv->minor->dev;
mutex_lock(&dev->struct_mutex);
ret = drm_add_user_object(file_priv, &lock->base, 0);
lock->base.remove = &drm_bo_write_lock_remove;
lock->base.type = drm_lock_type;
if (ret)
(void)__drm_bo_write_unlock(lock);
mutex_unlock(&dev->struct_mutex);
return ret;
}
int drm_bo_write_unlock(struct drm_bo_lock *lock, struct drm_file *file_priv)
{
struct drm_device *dev = file_priv->minor->dev;
struct drm_ref_object *ro;
mutex_lock(&dev->struct_mutex);
if (lock->base.owner != file_priv) {
mutex_unlock(&dev->struct_mutex);
return -EINVAL;
}
ro = drm_lookup_ref_object(file_priv, &lock->base, _DRM_REF_USE);
BUG_ON(!ro);
drm_remove_ref_object(file_priv, ro);
lock->base.owner = NULL;
mutex_unlock(&dev->struct_mutex);
return 0;
}
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