ttm_bo_api.h

/**************************************************************************
 *
 * 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
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 * permit persons to whom the Software is furnished to do so, subject to
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 * The above copyright notice and this permission notice (including the
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 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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/*
 * Authors: Thomas Hellstrom <thellstrom-at-vmware-dot-com>
 */

#ifndef _TTM_BO_API_H_
#define _TTM_BO_API_H_

#include <drm/drm_hashtab.h>
#include <drm/drm_vma_manager.h>
#include <linux/kref.h>
#include <linux/list.h>
#include <linux/wait.h>
#include <linux/mutex.h>
#include <linux/mm.h>
#include <linux/bitmap.h>
#include <linux/reservation.h>

struct ttm_bo_device;

struct drm_mm_node;

struct ttm_placement;

struct ttm_place;

/**
 * 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;
	phys_addr_t	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.
 * @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.
 * @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.
 * @moving: Fence set when BO is moving
 * @vma_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.
 * @wu_mutex: Wait unreserved mutex.
 *
 * 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;
	size_t acc_size;

	/**
	* Members not needing protection.
	*/

	struct kref kref;
	struct kref list_kref;

	/**
	 * Members protected by the bo::resv::reserved lock.
	 */

	struct ttm_mem_reg mem;
	struct file *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;

	/**
	 * Members protected by a bo reservation.
	 */

	struct dma_fence *moving;

	struct drm_vma_offset_node vma_node;

	unsigned priority;

	/**
	 * 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.
	 */

	uint64_t offset; /* GPU address space is independent of CPU word size */

	struct sg_table *sg;

	struct reservation_object *resv;
	struct reservation_object ttm_resv;
	struct mutex wu_mutex;
};

/**
 * 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 page *page;
	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;
};

/**
 * struct ttm_operation_ctx
 *
 * @interruptible: Sleep interruptible if sleeping.
 * @no_wait_gpu: Return immediately if the GPU is busy.
 *
 * Context for TTM operations like changing buffer placement or general memory
 * allocation.
 */
struct ttm_operation_ctx {
	bool interruptible;
	bool no_wait_gpu;
	uint64_t bytes_moved;
};

/**
 * 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.
 */
int ttm_bo_wait(struct ttm_buffer_object *bo, bool interruptible, bool no_wait);

/**
 * ttm_bo_mem_compat - Check if proposed placement is compatible with a bo
 *
 * @placement:  Return immediately if buffer is busy.
 * @mem:  The struct ttm_mem_reg indicating the region where the bo resides
 * @new_flags: Describes compatible placement found
 *
 * Returns true if the placement is compatible
 */
bool ttm_bo_mem_compat(struct ttm_placement *placement, struct ttm_mem_reg *mem,
		       uint32_t *new_flags);

/**
 * ttm_bo_validate
 *
 * @bo: The buffer object.
 * @placement: Proposed placement for the buffer object.
 * @ctx: validation parameters.
 *
 * 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.
 */
int ttm_bo_validate(struct ttm_buffer_object *bo,
		    struct ttm_placement *placement,
		    struct ttm_operation_ctx *ctx);

/**
 * ttm_bo_unref
 *
 * @bo: The buffer object.
 *
 * Unreference and clear a pointer to a buffer object.
 */
void ttm_bo_unref(struct ttm_buffer_object **bo);

/**
 * 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.
 */
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.
 */
void ttm_bo_del_from_lru(struct ttm_buffer_object *bo);

/**
 * ttm_bo_move_to_lru_tail
 *
 * @bo: The buffer object.
 *
 * Move this BO to the tail of 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 used to make a BO less likely to be considered for eviction.
 */
void ttm_bo_move_to_lru_tail(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
 */
int ttm_bo_lock_delayed_workqueue(struct ttm_bo_device *bdev);

/**
 * ttm_bo_unlock_delayed_workqueue
 *
 * Allows the delayed workqueue to run.
 */
void ttm_bo_unlock_delayed_workqueue(struct ttm_bo_device *bdev, int resched);

/**
 * ttm_bo_eviction_valuable
 *
 * @bo: The buffer object to evict
 * @place: the placement we need to make room for
 *
 * Check if it is valuable to evict the BO to make room for the given placement.
 */
bool ttm_bo_eviction_valuable(struct ttm_buffer_object *bo,
			      const struct ttm_place *place);

/**
 * 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.
 */
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.
 */
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_reserved
 *
 * @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.
 * @ctx: TTM operation context for memory allocation.
 * @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.
 * @resv: Pointer to a reservation_object, or NULL to let ttm allocate one.
 * @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 caller owns an object kref to @bo. The kref and
 * list_kref are usually set to 1, but note that in some situations, other
 * tasks may already be holding references to @bo as well.
 * Furthermore, if resv == NULL, the buffer's reservation lock will be held,
 * and it is the caller's responsibility to call ttm_bo_unreserve.
 *
 * 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.
 */

int ttm_bo_init_reserved(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,
			 struct ttm_operation_ctx *ctx,
			 struct file *persistent_swap_storage,
			 size_t acc_size,
			 struct sg_table *sg,
			 struct reservation_object *resv,
			 void (*destroy) (struct ttm_buffer_object *));

/**
 * 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.
 * @resv: Pointer to a reservation_object, or NULL to let ttm allocate one.
 * @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 caller owns an object kref to @bo. The kref and
 * list_kref are usually set to 1, but note that in some situations, other
 * tasks may already be holding references to @bo as well.
 *
 * 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.
 */
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 file *persistent_swap_storage, size_t acc_size,
		struct sg_table *sg, struct reservation_object *resv,
		void (*destroy) (struct ttm_buffer_object *));

/**
 * ttm_bo_create
 *
 * @bdev: Pointer to a ttm_bo_device struct.
 * @size: Requested size of buffer object.
 * @type: Requested type of buffer object.
 * @placement: Initial placement.
 * @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.
 */
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 file *persistent_swap_storage,
		  struct ttm_buffer_object **p_bo);

/**
 * 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.
 */
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.
 */
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.
 */
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.
 */
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.
 */
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.
 */
int ttm_fbdev_mmap(struct vm_area_struct *vma, struct ttm_buffer_object *bo);

/**
 * ttm_bo_default_iomem_pfn - get a pfn for a page offset
 *
 * @bo: the BO we need to look up the pfn for
 * @page_offset: offset inside the BO to look up.
 *
 * Calculate the PFN for iomem based mappings during page fault
 */
unsigned long ttm_bo_default_io_mem_pfn(struct ttm_buffer_object *bo,
				        unsigned long page_offset);

/**
 * 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.
 */
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.
 */
ssize_t ttm_bo_io(struct ttm_bo_device *bdev, struct file *filp,
		  const char __user *wbuf, char __user *rbuf,
		  size_t count, loff_t *f_pos, bool write);

void ttm_bo_swapout_all(struct ttm_bo_device *bdev);
int ttm_bo_wait_unreserved(struct ttm_buffer_object *bo);
#endif