text: /**************************************************************************
   *
   * Copyright (c) 2006-2009 VMware, Inc., Palo Alto, CA., 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 Hellstrom <thellstrom-at-vmware-dot-com>
   */
  /* $FreeBSD: head/sys/dev/drm2/ttm/ttm_bo_api.h 247835 2013-03-05 09:49:34Z kib $ */
  
  #ifndef _TTM_BO_API_H_
  #define _TTM_BO_API_H_
  
  #include <drm/drmP.h>
  #include <drm/drm_hashtab.h>
  #include <linux/kref.h>
  #include <linux/list.h>
  #include <linux/wait.h>
  
  struct ttm_bo_device;
  
  struct drm_mm_node;
  
  
  /**
   * struct ttm_placement
   *
   * @fpfn:		first valid page frame number to put the object
   * @lpfn:		last valid page frame number to put the object
   * @num_placement:	number of preferred placements
   * @placement:		preferred placements
   * @num_busy_placement:	number of preferred placements when need to evict buffer
   * @busy_placement:	preferred placements when need to evict buffer
   *
   * Structure indicating the placement you request for an object.
   */
  struct ttm_placement {
  	unsigned	fpfn;
  	unsigned	lpfn;
  	unsigned	num_placement;
  	const uint32_t	*placement;
  	unsigned	num_busy_placement;
  	const uint32_t	*busy_placement;
  };
  
  /**
   * struct ttm_bus_placement
   *
   * @addr:		mapped virtual address
   * @base:		bus base address
   * @is_iomem:		is this io memory ?
   * @size:		size in byte
   * @offset:		offset from the base address
   * @io_reserved_vm:     The VM system has a refcount in @io_reserved_count
   * @io_reserved_count:  Refcounting the numbers of callers to ttm_mem_io_reserve
   *
   * Structure indicating the bus placement of an object.
   */
  struct ttm_bus_placement {
  	void		*addr;
  	unsigned long	base;
  	unsigned long	size;
  	unsigned long	offset;
  	bool		is_iomem;
  	bool		io_reserved_vm;
  	uint64_t        io_reserved_count;
  };
  
  
  /**
   * struct ttm_mem_reg
   *
   * @mm_node: Memory manager node.
   * @size: Requested size of memory region.
   * @num_pages: Actual size of memory region in pages.
   * @page_alignment: Page alignment.
   * @placement: Placement flags.
   * @bus: Placement on io bus accessible to the CPU
   *
   * Structure indicating the placement and space resources used by a
   * buffer object.
   */
  
  struct ttm_mem_reg {
  	void *mm_node;
  	unsigned long start;
  	unsigned long size;
  	unsigned long num_pages;
  	uint32_t page_alignment;
  	uint32_t mem_type;
  	uint32_t placement;
  	struct ttm_bus_placement bus;
  };
  
  /**
   * enum ttm_bo_type
   *
   * @ttm_bo_type_device:	These are 'normal' buffers that can
   * be mmapped by user space. Each of these bos occupy a slot in the
   * device address space, that can be used for normal vm operations.
   *
   * @ttm_bo_type_kernel: These buffers are like ttm_bo_type_device buffers,
   * but they cannot be accessed from user-space. For kernel-only use.
   *
   * @ttm_bo_type_sg: Buffer made from dmabuf sg table shared with another
   * driver.
   */
  
  enum ttm_bo_type {
  	ttm_bo_type_device,
  	ttm_bo_type_kernel,
  	ttm_bo_type_sg
  };
  
  struct ttm_tt;
  
  /**
   * struct ttm_buffer_object
   *
   * @bdev: Pointer to the buffer object device structure.
   * @type: The bo type.
   * @destroy: Destruction function. If NULL, kfree is used.
   * @num_pages: Actual number of pages.
   * @addr_space_offset: Address space offset.
   * @acc_size: Accounted size for this object.
   * @kref: Reference count of this buffer object. When this refcount reaches
   * zero, the object is put on the delayed delete list.
   * @list_kref: List reference count of this buffer object. This member is
   * used to avoid destruction while the buffer object is still on a list.
   * Lru lists may keep one refcount, the delayed delete list, and kref != 0
   * keeps one refcount. When this refcount reaches zero,
   * the object is destroyed.
   * @event_queue: Queue for processes waiting on buffer object status change.
   * @mem: structure describing current placement.
   * @persistent_swap_storage: Usually the swap storage is deleted for buffers
   * pinned in physical memory. If this behaviour is not desired, this member
   * holds a pointer to a persistent shmem object.
   * @ttm: TTM structure holding system pages.
   * @evicted: Whether the object was evicted without user-space knowing.
   * @cpu_writes: For synchronization. Number of cpu writers.
   * @lru: List head for the lru list.
   * @ddestroy: List head for the delayed destroy list.
   * @swap: List head for swap LRU list.
   * @val_seq: Sequence of the validation holding the @reserved lock.
   * Used to avoid starvation when many processes compete to validate the
   * buffer. This member is protected by the bo_device::lru_lock.
   * @seq_valid: The value of @val_seq is valid. This value is protected by
   * the bo_device::lru_lock.
   * @reserved: Deadlock-free lock used for synchronization state transitions.
   * @sync_obj: Pointer to a synchronization object.
   * @priv_flags: Flags describing buffer object internal state.
   * @vm_rb: Rb node for the vm rb tree.
   * @vm_node: Address space manager node.
   * @offset: The current GPU offset, which can have different meanings
   * depending on the memory type. For SYSTEM type memory, it should be 0.
   * @cur_placement: Hint of current placement.
   *
   * Base class for TTM buffer object, that deals with data placement and CPU
   * mappings. GPU mappings are really up to the driver, but for simpler GPUs
   * the driver can usually use the placement offset @offset directly as the
   * GPU virtual address. For drivers implementing multiple
   * GPU memory manager contexts, the driver should manage the address space
   * in these contexts separately and use these objects to get the correct
   * placement and caching for these GPU maps. This makes it possible to use
   * these objects for even quite elaborate memory management schemes.
   * The destroy member, the API visibility of this object makes it possible
   * to derive driver specific types.
   */
  
  struct ttm_buffer_object {
  	/**
  	 * Members constant at init.
  	 */
  
  	struct ttm_bo_global *glob;
  	struct ttm_bo_device *bdev;
  	enum ttm_bo_type type;
  	void (*destroy) (struct ttm_buffer_object *);
  	unsigned long num_pages;
  	uint64_t addr_space_offset;
  	size_t acc_size;
  
  	/**
  	* Members not needing protection.
  	*/
  
  	struct kref kref;
  	struct kref list_kref;
  
  	wait_queue_head_t event_queue;
  
  	/**
  	 * Members protected by the bo::reserved lock.
  	 */
  
  	struct ttm_mem_reg mem;
  	struct vm_object *persistent_swap_storage;
  	struct ttm_tt *ttm;
  	bool evicted;
  
  	/**
  	 * Members protected by the bo::reserved lock only when written to.
  	 */
  
  	atomic_t cpu_writers;
  
  	/**
  	 * Members protected by the bdev::lru_lock.
  	 */
  
  	struct list_head lru;
  	struct list_head ddestroy;
  	struct list_head swap;
  	struct list_head io_reserve_lru;
  	uint32_t val_seq;
  	bool seq_valid;
  
  	/**
  	 * Members protected by the bdev::lru_lock
  	 * only when written to.
  	 */
  
  	atomic_t reserved;
  
  	/**
  	 * Members protected by struct buffer_object_device::fence_lock
  	 * In addition, setting sync_obj to anything else
  	 * than NULL requires bo::reserved to be held. This allows for
  	 * checking NULL while reserved but not holding the mentioned lock.
  	 */
  
  	void *sync_obj;
  	unsigned long priv_flags;
  
  	/**
  	 * Members protected by the bdev::vm_lock
  	 */
  
  	RB_ENTRY(ttm_buffer_object) vm_rb;
  	struct drm_mm_node *vm_node;
  
  
  	/**
  	 * Special members that are protected by the reserve lock
  	 * and the bo::lock when written to. Can be read with
  	 * either of these locks held.
  	 */
  
  	unsigned long offset;
  	uint32_t cur_placement;
  
  	struct sg_table *sg;
  };
  
  /**
   * struct ttm_bo_kmap_obj
   *
   * @virtual: The current kernel virtual address.
   * @page: The page when kmap'ing a single page.
   * @bo_kmap_type: Type of bo_kmap.
   *
   * Object describing a kernel mapping. Since a TTM bo may be located
   * in various memory types with various caching policies, the
   * mapping can either be an ioremap, a vmap, a kmap or part of a
   * premapped region.
   */
  
  #define TTM_BO_MAP_IOMEM_MASK 0x80
  struct ttm_bo_kmap_obj {
  	void *virtual;
  	struct vm_page *page;
  	struct sf_buf *sf;
  	int num_pages;
  	unsigned long size;
  	enum {
  		ttm_bo_map_iomap        = 1 | TTM_BO_MAP_IOMEM_MASK,
  		ttm_bo_map_vmap         = 2,
  		ttm_bo_map_kmap         = 3,
  		ttm_bo_map_premapped    = 4 | TTM_BO_MAP_IOMEM_MASK,
  	} bo_kmap_type;
  	struct ttm_buffer_object *bo;
  };
  
  /**
   * ttm_bo_reference - reference a struct ttm_buffer_object
   *
   * @bo: The buffer object.
   *
   * Returns a refcounted pointer to a buffer object.
   */
  
  static inline struct ttm_buffer_object *
  ttm_bo_reference(struct ttm_buffer_object *bo)
  {
  	kref_get(&bo->kref);
  	return bo;
  }
  
  /**
   * ttm_bo_wait - wait for buffer idle.
   *
   * @bo:  The buffer object.
   * @interruptible:  Use interruptible wait.
   * @no_wait:  Return immediately if buffer is busy.
   *
   * This function must be called with the bo::mutex held, and makes
   * sure any previous rendering to the buffer is completed.
   * Note: It might be necessary to block validations before the
   * wait by reserving the buffer.
   * Returns -EBUSY if no_wait is true and the buffer is busy.
   * Returns -ERESTARTSYS if interrupted by a signal.
   */
  extern int ttm_bo_wait(struct ttm_buffer_object *bo, bool lazy,
  		       bool interruptible, bool no_wait);
  /**
   * ttm_bo_validate
   *
   * @bo: The buffer object.
   * @placement: Proposed placement for the buffer object.
   * @interruptible: Sleep interruptible if sleeping.
   * @no_wait_gpu: Return immediately if the GPU is busy.
   *
   * Changes placement and caching policy of the buffer object
   * according proposed placement.
   * Returns
   * -EINVAL on invalid proposed placement.
   * -ENOMEM on out-of-memory condition.
   * -EBUSY if no_wait is true and buffer busy.
   * -ERESTARTSYS if interrupted by a signal.
   */
  extern int ttm_bo_validate(struct ttm_buffer_object *bo,
  				struct ttm_placement *placement,
  				bool interruptible,
  				bool no_wait_gpu);
  
  /**
   * ttm_bo_unref
   *
   * @bo: The buffer object.
   *
   * Unreference and clear a pointer to a buffer object.
   */
  extern void ttm_bo_unref(struct ttm_buffer_object **bo);
  
  
  /**
   * ttm_bo_list_ref_sub
   *
   * @bo: The buffer object.
   * @count: The number of references with which to decrease @bo::list_kref;
   * @never_free: The refcount should not reach zero with this operation.
   *
   * Release @count lru list references to this buffer object.
   */
  extern void ttm_bo_list_ref_sub(struct ttm_buffer_object *bo, int count,
  				bool never_free);
  
  /**
   * ttm_bo_add_to_lru
   *
   * @bo: The buffer object.
   *
   * Add this bo to the relevant mem type lru and, if it's backed by
   * system pages (ttms) to the swap list.
   * This function must be called with struct ttm_bo_global::lru_lock held, and
   * is typically called immediately prior to unreserving a bo.
   */
  extern void ttm_bo_add_to_lru(struct ttm_buffer_object *bo);
  
  /**
   * ttm_bo_del_from_lru
   *
   * @bo: The buffer object.
   *
   * Remove this bo from all lru lists used to lookup and reserve an object.
   * This function must be called with struct ttm_bo_global::lru_lock held,
   * and is usually called just immediately after the bo has been reserved to
   * avoid recursive reservation from lru lists.
   */
  extern int ttm_bo_del_from_lru(struct ttm_buffer_object *bo);
  
  
  /**
   * ttm_bo_lock_delayed_workqueue
   *
   * Prevent the delayed workqueue from running.
   * Returns
   * True if the workqueue was queued at the time
   */
  extern int ttm_bo_lock_delayed_workqueue(struct ttm_bo_device *bdev);
  
  /**
   * ttm_bo_unlock_delayed_workqueue
   *
   * Allows the delayed workqueue to run.
   */
  extern void ttm_bo_unlock_delayed_workqueue(struct ttm_bo_device *bdev,
  					    int resched);
  
  /**
   * ttm_bo_synccpu_write_grab
   *
   * @bo: The buffer object:
   * @no_wait: Return immediately if buffer is busy.
   *
   * Synchronizes a buffer object for CPU RW access. This means
   * command submission that affects the buffer will return -EBUSY
   * until ttm_bo_synccpu_write_release is called.
   *
   * Returns
   * -EBUSY if the buffer is busy and no_wait is true.
   * -ERESTARTSYS if interrupted by a signal.
   */
  extern int
  ttm_bo_synccpu_write_grab(struct ttm_buffer_object *bo, bool no_wait);
  
  /**
   * ttm_bo_synccpu_write_release:
   *
   * @bo : The buffer object.
   *
   * Releases a synccpu lock.
   */
  extern void ttm_bo_synccpu_write_release(struct ttm_buffer_object *bo);
  
  /**
   * ttm_bo_acc_size
   *
   * @bdev: Pointer to a ttm_bo_device struct.
   * @bo_size: size of the buffer object in byte.
   * @struct_size: size of the structure holding buffer object datas
   *
   * Returns size to account for a buffer object
   */
  size_t ttm_bo_acc_size(struct ttm_bo_device *bdev,
  		       unsigned long bo_size,
  		       unsigned struct_size);
  size_t ttm_bo_dma_acc_size(struct ttm_bo_device *bdev,
  			   unsigned long bo_size,
  			   unsigned struct_size);
  
  /**
   * ttm_bo_init
   *
   * @bdev: Pointer to a ttm_bo_device struct.
   * @bo: Pointer to a ttm_buffer_object to be initialized.
   * @size: Requested size of buffer object.
   * @type: Requested type of buffer object.
   * @flags: Initial placement flags.
   * @page_alignment: Data alignment in pages.
   * @interruptible: If needing to sleep to wait for GPU resources,
   * sleep interruptible.
   * @persistent_swap_storage: Usually the swap storage is deleted for buffers
   * pinned in physical memory. If this behaviour is not desired, this member
   * holds a pointer to a persistent shmem object. Typically, this would
   * point to the shmem object backing a GEM object if TTM is used to back a
   * GEM user interface.
   * @acc_size: Accounted size for this object.
   * @destroy: Destroy function. Use NULL for kfree().
   *
   * This function initializes a pre-allocated struct ttm_buffer_object.
   * As this object may be part of a larger structure, this function,
   * together with the @destroy function,
   * enables driver-specific objects derived from a ttm_buffer_object.
   * On successful return, the object kref and list_kref are set to 1.
   * If a failure occurs, the function will call the @destroy function, or
   * kfree() if @destroy is NULL. Thus, after a failure, dereferencing @bo is
   * illegal and will likely cause memory corruption.
   *
   * Returns
   * -ENOMEM: Out of memory.
   * -EINVAL: Invalid placement flags.
   * -ERESTARTSYS: Interrupted by signal while sleeping waiting for resources.
   */
  
  extern int ttm_bo_init(struct ttm_bo_device *bdev,
  			struct ttm_buffer_object *bo,
  			unsigned long size,
  			enum ttm_bo_type type,
  			struct ttm_placement *placement,
  			uint32_t page_alignment,
  			bool interrubtible,
  			struct vm_object *persistent_swap_storage,
  			size_t acc_size,
  			struct sg_table *sg,
  			void (*destroy) (struct ttm_buffer_object *));
  
  /**
   * ttm_bo_synccpu_object_init
   *
   * @bdev: Pointer to a ttm_bo_device struct.
   * @bo: Pointer to a ttm_buffer_object to be initialized.
   * @size: Requested size of buffer object.
   * @type: Requested type of buffer object.
   * @flags: Initial placement flags.
   * @page_alignment: Data alignment in pages.
   * @interruptible: If needing to sleep while waiting for GPU resources,
   * sleep interruptible.
   * @persistent_swap_storage: Usually the swap storage is deleted for buffers
   * pinned in physical memory. If this behaviour is not desired, this member
   * holds a pointer to a persistent shmem object. Typically, this would
   * point to the shmem object backing a GEM object if TTM is used to back a
   * GEM user interface.
   * @p_bo: On successful completion *p_bo points to the created object.
   *
   * This function allocates a ttm_buffer_object, and then calls ttm_bo_init
   * on that object. The destroy function is set to kfree().
   * Returns
   * -ENOMEM: Out of memory.
   * -EINVAL: Invalid placement flags.
   * -ERESTARTSYS: Interrupted by signal while waiting for resources.
   */
  
  extern int ttm_bo_create(struct ttm_bo_device *bdev,
  				unsigned long size,
  				enum ttm_bo_type type,
  				struct ttm_placement *placement,
  				uint32_t page_alignment,
  				bool interruptible,
  				struct vm_object *persistent_swap_storage,
  				struct ttm_buffer_object **p_bo);
  
  /**
   * ttm_bo_check_placement
   *
   * @bo:		the buffer object.
   * @placement:	placements
   *
   * Performs minimal validity checking on an intended change of
   * placement flags.
   * Returns
   * -EINVAL: Intended change is invalid or not allowed.
   */
  extern int ttm_bo_check_placement(struct ttm_buffer_object *bo,
  					struct ttm_placement *placement);
  
  /**
   * ttm_bo_init_mm
   *
   * @bdev: Pointer to a ttm_bo_device struct.
   * @mem_type: The memory type.
   * @p_size: size managed area in pages.
   *
   * Initialize a manager for a given memory type.
   * Note: if part of driver firstopen, it must be protected from a
   * potentially racing lastclose.
   * Returns:
   * -EINVAL: invalid size or memory type.
   * -ENOMEM: Not enough memory.
   * May also return driver-specified errors.
   */
  
  extern int ttm_bo_init_mm(struct ttm_bo_device *bdev, unsigned type,
  				unsigned long p_size);
  /**
   * ttm_bo_clean_mm
   *
   * @bdev: Pointer to a ttm_bo_device struct.
   * @mem_type: The memory type.
   *
   * Take down a manager for a given memory type after first walking
   * the LRU list to evict any buffers left alive.
   *
   * Normally, this function is part of lastclose() or unload(), and at that
   * point there shouldn't be any buffers left created by user-space, since
   * there should've been removed by the file descriptor release() method.
   * However, before this function is run, make sure to signal all sync objects,
   * and verify that the delayed delete queue is empty. The driver must also
   * make sure that there are no NO_EVICT buffers present in this memory type
   * when the call is made.
   *
   * If this function is part of a VT switch, the caller must make sure that
   * there are no appications currently validating buffers before this
   * function is called. The caller can do that by first taking the
   * struct ttm_bo_device::ttm_lock in write mode.
   *
   * Returns:
   * -EINVAL: invalid or uninitialized memory type.
   * -EBUSY: There are still buffers left in this memory type.
   */
  
  extern int ttm_bo_clean_mm(struct ttm_bo_device *bdev, unsigned mem_type);
  
  /**
   * ttm_bo_evict_mm
   *
   * @bdev: Pointer to a ttm_bo_device struct.
   * @mem_type: The memory type.
   *
   * Evicts all buffers on the lru list of the memory type.
   * This is normally part of a VT switch or an
   * out-of-memory-space-due-to-fragmentation handler.
   * The caller must make sure that there are no other processes
   * currently validating buffers, and can do that by taking the
   * struct ttm_bo_device::ttm_lock in write mode.
   *
   * Returns:
   * -EINVAL: Invalid or uninitialized memory type.
   * -ERESTARTSYS: The call was interrupted by a signal while waiting to
   * evict a buffer.
   */
  
  extern int ttm_bo_evict_mm(struct ttm_bo_device *bdev, unsigned mem_type);
  
  /**
   * ttm_kmap_obj_virtual
   *
   * @map: A struct ttm_bo_kmap_obj returned from ttm_bo_kmap.
   * @is_iomem: Pointer to an integer that on return indicates 1 if the
   * virtual map is io memory, 0 if normal memory.
   *
   * Returns the virtual address of a buffer object area mapped by ttm_bo_kmap.
   * If *is_iomem is 1 on return, the virtual address points to an io memory area,
   * that should strictly be accessed by the iowriteXX() and similar functions.
   */
  
  static inline void *ttm_kmap_obj_virtual(struct ttm_bo_kmap_obj *map,
  					 bool *is_iomem)
  {
  	*is_iomem = !!(map->bo_kmap_type & TTM_BO_MAP_IOMEM_MASK);
  	return map->virtual;
  }
  
  /**
   * ttm_bo_kmap
   *
   * @bo: The buffer object.
   * @start_page: The first page to map.
   * @num_pages: Number of pages to map.
   * @map: pointer to a struct ttm_bo_kmap_obj representing the map.
   *
   * Sets up a kernel virtual mapping, using ioremap, vmap or kmap to the
   * data in the buffer object. The ttm_kmap_obj_virtual function can then be
   * used to obtain a virtual address to the data.
   *
   * Returns
   * -ENOMEM: Out of memory.
   * -EINVAL: Invalid range.
   */
  
  extern int ttm_bo_kmap(struct ttm_buffer_object *bo, unsigned long start_page,
  		       unsigned long num_pages, struct ttm_bo_kmap_obj *map);
  
  /**
   * ttm_bo_kunmap
   *
   * @map: Object describing the map to unmap.
   *
   * Unmaps a kernel map set up by ttm_bo_kmap.
   */
  
  extern void ttm_bo_kunmap(struct ttm_bo_kmap_obj *map);
  
  /**
   * ttm_fbdev_mmap - mmap fbdev memory backed by a ttm buffer object.
   *
   * @vma:       vma as input from the fbdev mmap method.
   * @bo:        The bo backing the address space. The address space will
   * have the same size as the bo, and start at offset 0.
   *
   * This function is intended to be called by the fbdev mmap method
   * if the fbdev address space is to be backed by a bo.
   */
  
  /* XXXKIB
  extern int ttm_fbdev_mmap(struct vm_area_struct *vma,
  			  struct ttm_buffer_object *bo);
  */
  /**
   * ttm_bo_mmap - mmap out of the ttm device address space.
   *
   * @filp:      filp as input from the mmap method.
   * @vma:       vma as input from the mmap method.
   * @bdev:      Pointer to the ttm_bo_device with the address space manager.
   *
   * This function is intended to be called by the device mmap method.
   * if the device address space is to be backed by the bo manager.
   */
  /* XXXKIB
  extern int ttm_bo_mmap(struct file *filp, struct vm_area_struct *vma,
  		       struct ttm_bo_device *bdev);
  */
  /**
   * ttm_bo_io
   *
   * @bdev:      Pointer to the struct ttm_bo_device.
   * @filp:      Pointer to the struct file attempting to read / write.
   * @wbuf:      User-space pointer to address of buffer to write. NULL on read.
   * @rbuf:      User-space pointer to address of buffer to read into.
   * Null on write.
   * @count:     Number of bytes to read / write.
   * @f_pos:     Pointer to current file position.
   * @write:     1 for read, 0 for write.
   *
   * This function implements read / write into ttm buffer objects, and is
   * intended to
   * be called from the fops::read and fops::write method.
   * Returns:
   * See man (2) write, man(2) read. In particular,
   * the function may return -ERESTARTSYS if
   * interrupted by a signal.
   */
  
  extern ssize_t ttm_bo_io(struct ttm_bo_device *bdev, struct file *filp,
  			 const char *wbuf, char *rbuf,
  			 size_t count, off_t *f_pos, bool write);
  
  extern void ttm_bo_swapout_all(struct ttm_bo_device *bdev);
  
  /**
   * ttm_bo_is_reserved - return an indication if a ttm buffer object is reserved
   *
   * @bo:     The buffer object to check.
   *
   * This function returns an indication if a bo is reserved or not, and should
   * only be used to print an error when it is not from incorrect api usage, since
   * there's no guarantee that it is the caller that is holding the reservation.
   */
  static inline bool ttm_bo_is_reserved(struct ttm_buffer_object *bo)
  {
  	return atomic_read(&bo->reserved);
  }
  
  #endif
  