--- /dev/null
+/**************************************************************************
+ *
+ * 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->head->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->head->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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