xref: /linux/drivers/gpu/drm/i915/gem/i915_gem_object_types.h (revision 84b9b44b)

/*
 * SPDX-License-Identifier: MIT
 *
 * Copyright © 2016 Intel Corporation
 */

#ifndef __I915_GEM_OBJECT_TYPES_H__
#define __I915_GEM_OBJECT_TYPES_H__

#include <linux/mmu_notifier.h>

#include <drm/drm_gem.h>
#include <drm/ttm/ttm_bo.h>
#include <uapi/drm/i915_drm.h>

#include "i915_active.h"
#include "i915_selftest.h"
#include "i915_vma_resource.h"

struct drm_i915_gem_object;
struct intel_fronbuffer;
struct intel_memory_region;

/*
 * struct i915_lut_handle tracks the fast lookups from handle to vma used
 * for execbuf. Although we use a radixtree for that mapping, in order to
 * remove them as the object or context is closed, we need a secondary list
 * and a translation entry (i915_lut_handle).
 */
struct i915_lut_handle {
	struct list_head obj_link;
	struct i915_gem_context *ctx;
	u32 handle;
};

struct drm_i915_gem_object_ops {
	unsigned int flags;
#define I915_GEM_OBJECT_IS_SHRINKABLE			BIT(1)
/* Skip the shrinker management in set_pages/unset_pages */
#define I915_GEM_OBJECT_SELF_MANAGED_SHRINK_LIST	BIT(2)
#define I915_GEM_OBJECT_IS_PROXY			BIT(3)
#define I915_GEM_OBJECT_NO_MMAP				BIT(4)

	/* Interface between the GEM object and its backing storage.
	 * get_pages() is called once prior to the use of the associated set
	 * of pages before to binding them into the GTT, and put_pages() is
	 * called after we no longer need them. As we expect there to be
	 * associated cost with migrating pages between the backing storage
	 * and making them available for the GPU (e.g. clflush), we may hold
	 * onto the pages after they are no longer referenced by the GPU
	 * in case they may be used again shortly (for example migrating the
	 * pages to a different memory domain within the GTT). put_pages()
	 * will therefore most likely be called when the object itself is
	 * being released or under memory pressure (where we attempt to
	 * reap pages for the shrinker).
	 */
	int (*get_pages)(struct drm_i915_gem_object *obj);
	void (*put_pages)(struct drm_i915_gem_object *obj,
			  struct sg_table *pages);
	int (*truncate)(struct drm_i915_gem_object *obj);
	/**
	 * shrink - Perform further backend specific actions to facilate
	 * shrinking.
	 * @obj: The gem object
	 * @flags: Extra flags to control shrinking behaviour in the backend
	 *
	 * Possible values for @flags:
	 *
	 * I915_GEM_OBJECT_SHRINK_WRITEBACK - Try to perform writeback of the
	 * backing pages, if supported.
	 *
	 * I915_GEM_OBJECT_SHRINK_NO_GPU_WAIT - Don't wait for the object to
	 * idle.  Active objects can be considered later. The TTM backend for
	 * example might have aync migrations going on, which don't use any
	 * i915_vma to track the active GTT binding, and hence having an unbound
	 * object might not be enough.
	 */
#define I915_GEM_OBJECT_SHRINK_WRITEBACK   BIT(0)
#define I915_GEM_OBJECT_SHRINK_NO_GPU_WAIT BIT(1)
	int (*shrink)(struct drm_i915_gem_object *obj, unsigned int flags);

	int (*pread)(struct drm_i915_gem_object *obj,
		     const struct drm_i915_gem_pread *arg);
	int (*pwrite)(struct drm_i915_gem_object *obj,
		      const struct drm_i915_gem_pwrite *arg);
	u64 (*mmap_offset)(struct drm_i915_gem_object *obj);
	void (*unmap_virtual)(struct drm_i915_gem_object *obj);

	int (*dmabuf_export)(struct drm_i915_gem_object *obj);

	/**
	 * adjust_lru - notify that the madvise value was updated
	 * @obj: The gem object
	 *
	 * The madvise value may have been updated, or object was recently
	 * referenced so act accordingly (Perhaps changing an LRU list etc).
	 */
	void (*adjust_lru)(struct drm_i915_gem_object *obj);

	/**
	 * delayed_free - Override the default delayed free implementation
	 */
	void (*delayed_free)(struct drm_i915_gem_object *obj);

	/**
	 * migrate - Migrate object to a different region either for
	 * pinning or for as long as the object lock is held.
	 */
	int (*migrate)(struct drm_i915_gem_object *obj,
		       struct intel_memory_region *mr,
		       unsigned int flags);

	void (*release)(struct drm_i915_gem_object *obj);

	const struct vm_operations_struct *mmap_ops;
	const char *name; /* friendly name for debug, e.g. lockdep classes */
};

/**
 * enum i915_cache_level - The supported GTT caching values for system memory
 * pages.
 *
 * These translate to some special GTT PTE bits when binding pages into some
 * address space. It also determines whether an object, or rather its pages are
 * coherent with the GPU, when also reading or writing through the CPU cache
 * with those pages.
 *
 * Userspace can also control this through struct drm_i915_gem_caching.
 */
enum i915_cache_level {
	/**
	 * @I915_CACHE_NONE:
	 *
	 * GPU access is not coherent with the CPU cache. If the cache is dirty
	 * and we need the underlying pages to be coherent with some later GPU
	 * access then we need to manually flush the pages.
	 *
	 * On shared LLC platforms reads and writes through the CPU cache are
	 * still coherent even with this setting. See also
	 * &drm_i915_gem_object.cache_coherent for more details. Due to this we
	 * should only ever use uncached for scanout surfaces, otherwise we end
	 * up over-flushing in some places.
	 *
	 * This is the default on non-LLC platforms.
	 */
	I915_CACHE_NONE = 0,
	/**
	 * @I915_CACHE_LLC:
	 *
	 * GPU access is coherent with the CPU cache. If the cache is dirty,
	 * then the GPU will ensure that access remains coherent, when both
	 * reading and writing through the CPU cache. GPU writes can dirty the
	 * CPU cache.
	 *
	 * Not used for scanout surfaces.
	 *
	 * Applies to both platforms with shared LLC(HAS_LLC), and snooping
	 * based platforms(HAS_SNOOP).
	 *
	 * This is the default on shared LLC platforms.  The only exception is
	 * scanout objects, where the display engine is not coherent with the
	 * CPU cache. For such objects I915_CACHE_NONE or I915_CACHE_WT is
	 * automatically applied by the kernel in pin_for_display, if userspace
	 * has not done so already.
	 */
	I915_CACHE_LLC,
	/**
	 * @I915_CACHE_L3_LLC:
	 *
	 * Explicitly enable the Gfx L3 cache, with coherent LLC.
	 *
	 * The Gfx L3 sits between the domain specific caches, e.g
	 * sampler/render caches, and the larger LLC. LLC is coherent with the
	 * GPU, but L3 is only visible to the GPU, so likely needs to be flushed
	 * when the workload completes.
	 *
	 * Not used for scanout surfaces.
	 *
	 * Only exposed on some gen7 + GGTT. More recent hardware has dropped
	 * this explicit setting, where it should now be enabled by default.
	 */
	I915_CACHE_L3_LLC,
	/**
	 * @I915_CACHE_WT:
	 *
	 * Write-through. Used for scanout surfaces.
	 *
	 * The GPU can utilise the caches, while still having the display engine
	 * be coherent with GPU writes, as a result we don't need to flush the
	 * CPU caches when moving out of the render domain. This is the default
	 * setting chosen by the kernel, if supported by the HW, otherwise we
	 * fallback to I915_CACHE_NONE. On the CPU side writes through the CPU
	 * cache still need to be flushed, to remain coherent with the display
	 * engine.
	 */
	I915_CACHE_WT,
};

enum i915_map_type {
	I915_MAP_WB = 0,
	I915_MAP_WC,
#define I915_MAP_OVERRIDE BIT(31)
	I915_MAP_FORCE_WB = I915_MAP_WB | I915_MAP_OVERRIDE,
	I915_MAP_FORCE_WC = I915_MAP_WC | I915_MAP_OVERRIDE,
};

enum i915_mmap_type {
	I915_MMAP_TYPE_GTT = 0,
	I915_MMAP_TYPE_WC,
	I915_MMAP_TYPE_WB,
	I915_MMAP_TYPE_UC,
	I915_MMAP_TYPE_FIXED,
};

struct i915_mmap_offset {
	struct drm_vma_offset_node vma_node;
	struct drm_i915_gem_object *obj;
	enum i915_mmap_type mmap_type;

	struct rb_node offset;
};

struct i915_gem_object_page_iter {
	struct scatterlist *sg_pos;
	unsigned int sg_idx; /* in pages, but 32bit eek! */

	struct radix_tree_root radix;
	struct mutex lock; /* protects this cache */
};

struct drm_i915_gem_object {
	/*
	 * We might have reason to revisit the below since it wastes
	 * a lot of space for non-ttm gem objects.
	 * In any case, always use the accessors for the ttm_buffer_object
	 * when accessing it.
	 */
	union {
		struct drm_gem_object base;
		struct ttm_buffer_object __do_not_access;
	};

	const struct drm_i915_gem_object_ops *ops;

	struct {
		/**
		 * @vma.lock: protect the list/tree of vmas
		 */
		spinlock_t lock;

		/**
		 * @vma.list: List of VMAs backed by this object
		 *
		 * The VMA on this list are ordered by type, all GGTT vma are
		 * placed at the head and all ppGTT vma are placed at the tail.
		 * The different types of GGTT vma are unordered between
		 * themselves, use the @vma.tree (which has a defined order
		 * between all VMA) to quickly find an exact match.
		 */
		struct list_head list;

		/**
		 * @vma.tree: Ordered tree of VMAs backed by this object
		 *
		 * All VMA created for this object are placed in the @vma.tree
		 * for fast retrieval via a binary search in
		 * i915_vma_instance(). They are also added to @vma.list for
		 * easy iteration.
		 */
		struct rb_root tree;
	} vma;

	/**
	 * @lut_list: List of vma lookup entries in use for this object.
	 *
	 * If this object is closed, we need to remove all of its VMA from
	 * the fast lookup index in associated contexts; @lut_list provides
	 * this translation from object to context->handles_vma.
	 */
	struct list_head lut_list;
	spinlock_t lut_lock; /* guards lut_list */

	/**
	 * @obj_link: Link into @i915_gem_ww_ctx.obj_list
	 *
	 * When we lock this object through i915_gem_object_lock() with a
	 * context, we add it to the list to ensure we can unlock everything
	 * when i915_gem_ww_ctx_backoff() or i915_gem_ww_ctx_fini() are called.
	 */
	struct list_head obj_link;
	/**
	 * @shared_resv_from: The object shares the resv from this vm.
	 */
	struct i915_address_space *shares_resv_from;

	union {
		struct rcu_head rcu;
		struct llist_node freed;
	};

	/**
	 * Whether the object is currently in the GGTT or any other supported
	 * fake offset mmap backed by lmem.
	 */
	unsigned int userfault_count;
	struct list_head userfault_link;

	struct {
		spinlock_t lock; /* Protects access to mmo offsets */
		struct rb_root offsets;
	} mmo;

	I915_SELFTEST_DECLARE(struct list_head st_link);

	unsigned long flags;
#define I915_BO_ALLOC_CONTIGUOUS  BIT(0)
#define I915_BO_ALLOC_VOLATILE    BIT(1)
#define I915_BO_ALLOC_CPU_CLEAR   BIT(2)
#define I915_BO_ALLOC_USER        BIT(3)
/* Object is allowed to lose its contents on suspend / resume, even if pinned */
#define I915_BO_ALLOC_PM_VOLATILE BIT(4)
/* Object needs to be restored early using memcpy during resume */
#define I915_BO_ALLOC_PM_EARLY    BIT(5)
/*
 * Object is likely never accessed by the CPU. This will prioritise the BO to be
 * allocated in the non-mappable portion of lmem. This is merely a hint, and if
 * dealing with userspace objects the CPU fault handler is free to ignore this.
 */
#define I915_BO_ALLOC_GPU_ONLY	  BIT(6)
#define I915_BO_ALLOC_CCS_AUX	  BIT(7)
#define I915_BO_ALLOC_FLAGS (I915_BO_ALLOC_CONTIGUOUS | \
			     I915_BO_ALLOC_VOLATILE | \
			     I915_BO_ALLOC_CPU_CLEAR | \
			     I915_BO_ALLOC_USER | \
			     I915_BO_ALLOC_PM_VOLATILE | \
			     I915_BO_ALLOC_PM_EARLY | \
			     I915_BO_ALLOC_GPU_ONLY | \
			     I915_BO_ALLOC_CCS_AUX)
#define I915_BO_READONLY          BIT(8)
#define I915_TILING_QUIRK_BIT     9 /* unknown swizzling; do not release! */
#define I915_BO_PROTECTED         BIT(10)
	/**
	 * @mem_flags - Mutable placement-related flags
	 *
	 * These are flags that indicate specifics of the memory region
	 * the object is currently in. As such they are only stable
	 * either under the object lock or if the object is pinned.
	 */
	unsigned int mem_flags;
#define I915_BO_FLAG_STRUCT_PAGE BIT(0) /* Object backed by struct pages */
#define I915_BO_FLAG_IOMEM       BIT(1) /* Object backed by IO memory */
	/**
	 * @cache_level: The desired GTT caching level.
	 *
	 * See enum i915_cache_level for possible values, along with what
	 * each does.
	 */
	unsigned int cache_level:3;
	/**
	 * @cache_coherent:
	 *
	 * Track whether the pages are coherent with the GPU if reading or
	 * writing through the CPU caches. The largely depends on the
	 * @cache_level setting.
	 *
	 * On platforms which don't have the shared LLC(HAS_SNOOP), like on Atom
	 * platforms, coherency must be explicitly requested with some special
	 * GTT caching bits(see enum i915_cache_level). When enabling coherency
	 * it does come at a performance and power cost on such platforms. On
	 * the flip side the kernel does not need to manually flush any buffers
	 * which need to be coherent with the GPU, if the object is not coherent
	 * i.e @cache_coherent is zero.
	 *
	 * On platforms that share the LLC with the CPU(HAS_LLC), all GT memory
	 * access will automatically snoop the CPU caches(even with CACHE_NONE).
	 * The one exception is when dealing with the display engine, like with
	 * scanout surfaces. To handle this the kernel will always flush the
	 * surface out of the CPU caches when preparing it for scanout.  Also
	 * note that since scanout surfaces are only ever read by the display
	 * engine we only need to care about flushing any writes through the CPU
	 * cache, reads on the other hand will always be coherent.
	 *
	 * Something strange here is why @cache_coherent is not a simple
	 * boolean, i.e coherent vs non-coherent. The reasoning for this is back
	 * to the display engine not being fully coherent. As a result scanout
	 * surfaces will either be marked as I915_CACHE_NONE or I915_CACHE_WT.
	 * In the case of seeing I915_CACHE_NONE the kernel makes the assumption
	 * that this is likely a scanout surface, and will set @cache_coherent
	 * as only I915_BO_CACHE_COHERENT_FOR_READ, on platforms with the shared
	 * LLC. The kernel uses this to always flush writes through the CPU
	 * cache as early as possible, where it can, in effect keeping
	 * @cache_dirty clean, so we can potentially avoid stalling when
	 * flushing the surface just before doing the scanout.  This does mean
	 * we might unnecessarily flush non-scanout objects in some places, but
	 * the default assumption is that all normal objects should be using
	 * I915_CACHE_LLC, at least on platforms with the shared LLC.
	 *
	 * Supported values:
	 *
	 * I915_BO_CACHE_COHERENT_FOR_READ:
	 *
	 * On shared LLC platforms, we use this for special scanout surfaces,
	 * where the display engine is not coherent with the CPU cache. As such
	 * we need to ensure we flush any writes before doing the scanout. As an
	 * optimisation we try to flush any writes as early as possible to avoid
	 * stalling later.
	 *
	 * Thus for scanout surfaces using I915_CACHE_NONE, on shared LLC
	 * platforms, we use:
	 *
	 *	cache_coherent = I915_BO_CACHE_COHERENT_FOR_READ
	 *
	 * While for normal objects that are fully coherent, including special
	 * scanout surfaces marked as I915_CACHE_WT, we use:
	 *
	 *	cache_coherent = I915_BO_CACHE_COHERENT_FOR_READ |
	 *			 I915_BO_CACHE_COHERENT_FOR_WRITE
	 *
	 * And then for objects that are not coherent at all we use:
	 *
	 *	cache_coherent = 0
	 *
	 * I915_BO_CACHE_COHERENT_FOR_WRITE:
	 *
	 * When writing through the CPU cache, the GPU is still coherent. Note
	 * that this also implies I915_BO_CACHE_COHERENT_FOR_READ.
	 */
#define I915_BO_CACHE_COHERENT_FOR_READ BIT(0)
#define I915_BO_CACHE_COHERENT_FOR_WRITE BIT(1)
	unsigned int cache_coherent:2;

	/**
	 * @cache_dirty:
	 *
	 * Track if we are we dirty with writes through the CPU cache for this
	 * object. As a result reading directly from main memory might yield
	 * stale data.
	 *
	 * This also ties into whether the kernel is tracking the object as
	 * coherent with the GPU, as per @cache_coherent, as it determines if
	 * flushing might be needed at various points.
	 *
	 * Another part of @cache_dirty is managing flushing when first
	 * acquiring the pages for system memory, at this point the pages are
	 * considered foreign, so the default assumption is that the cache is
	 * dirty, for example the page zeroing done by the kernel might leave
	 * writes though the CPU cache, or swapping-in, while the actual data in
	 * main memory is potentially stale.  Note that this is a potential
	 * security issue when dealing with userspace objects and zeroing. Now,
	 * whether we actually need apply the big sledgehammer of flushing all
	 * the pages on acquire depends on if @cache_coherent is marked as
	 * I915_BO_CACHE_COHERENT_FOR_WRITE, i.e that the GPU will be coherent
	 * for both reads and writes though the CPU cache.
	 *
	 * Note that on shared LLC platforms we still apply the heavy flush for
	 * I915_CACHE_NONE objects, under the assumption that this is going to
	 * be used for scanout.
	 *
	 * Update: On some hardware there is now also the 'Bypass LLC' MOCS
	 * entry, which defeats our @cache_coherent tracking, since userspace
	 * can freely bypass the CPU cache when touching the pages with the GPU,
	 * where the kernel is completely unaware. On such platform we need
	 * apply the sledgehammer-on-acquire regardless of the @cache_coherent.
	 *
	 * Special care is taken on non-LLC platforms, to prevent potential
	 * information leak. The driver currently ensures:
	 *
	 *   1. All userspace objects, by default, have @cache_level set as
	 *   I915_CACHE_NONE. The only exception is userptr objects, where we
	 *   instead force I915_CACHE_LLC, but we also don't allow userspace to
	 *   ever change the @cache_level for such objects. Another special case
	 *   is dma-buf, which doesn't rely on @cache_dirty,  but there we
	 *   always do a forced flush when acquiring the pages, if there is a
	 *   chance that the pages can be read directly from main memory with
	 *   the GPU.
	 *
	 *   2. All I915_CACHE_NONE objects have @cache_dirty initially true.
	 *
	 *   3. All swapped-out objects(i.e shmem) have @cache_dirty set to
	 *   true.
	 *
	 *   4. The @cache_dirty is never freely reset before the initial
	 *   flush, even if userspace adjusts the @cache_level through the
	 *   i915_gem_set_caching_ioctl.
	 *
	 *   5. All @cache_dirty objects(including swapped-in) are initially
	 *   flushed with a synchronous call to drm_clflush_sg in
	 *   __i915_gem_object_set_pages. The @cache_dirty can be freely reset
	 *   at this point. All further asynchronous clfushes are never security
	 *   critical, i.e userspace is free to race against itself.
	 */
	unsigned int cache_dirty:1;

	/* @is_dpt: Object houses a display page table (DPT) */
	unsigned int is_dpt:1;

	/**
	 * @read_domains: Read memory domains.
	 *
	 * These monitor which caches contain read/write data related to the
	 * object. When transitioning from one set of domains to another,
	 * the driver is called to ensure that caches are suitably flushed and
	 * invalidated.
	 */
	u16 read_domains;

	/**
	 * @write_domain: Corresponding unique write memory domain.
	 */
	u16 write_domain;

	struct intel_frontbuffer __rcu *frontbuffer;

	/** Current tiling stride for the object, if it's tiled. */
	unsigned int tiling_and_stride;
#define FENCE_MINIMUM_STRIDE 128 /* See i915_tiling_ok() */
#define TILING_MASK (FENCE_MINIMUM_STRIDE - 1)
#define STRIDE_MASK (~TILING_MASK)

	struct {
		/*
		 * Protects the pages and their use. Do not use directly, but
		 * instead go through the pin/unpin interfaces.
		 */
		atomic_t pages_pin_count;

		/**
		 * @shrink_pin: Prevents the pages from being made visible to
		 * the shrinker, while the shrink_pin is non-zero. Most users
		 * should pretty much never have to care about this, outside of
		 * some special use cases.
		 *
		 * By default most objects will start out as visible to the
		 * shrinker(if I915_GEM_OBJECT_IS_SHRINKABLE) as soon as the
		 * backing pages are attached to the object, like in
		 * __i915_gem_object_set_pages(). They will then be removed the
		 * shrinker list once the pages are released.
		 *
		 * The @shrink_pin is incremented by calling
		 * i915_gem_object_make_unshrinkable(), which will also remove
		 * the object from the shrinker list, if the pin count was zero.
		 *
		 * Callers will then typically call
		 * i915_gem_object_make_shrinkable() or
		 * i915_gem_object_make_purgeable() to decrement the pin count,
		 * and make the pages visible again.
		 */
		atomic_t shrink_pin;

		/**
		 * @ttm_shrinkable: True when the object is using shmem pages
		 * underneath. Protected by the object lock.
		 */
		bool ttm_shrinkable;

		/**
		 * @unknown_state: Indicate that the object is effectively
		 * borked. This is write-once and set if we somehow encounter a
		 * fatal error when moving/clearing the pages, and we are not
		 * able to fallback to memcpy/memset, like on small-BAR systems.
		 * The GPU should also be wedged (or in the process) at this
		 * point.
		 *
		 * Only valid to read this after acquiring the dma-resv lock and
		 * waiting for all DMA_RESV_USAGE_KERNEL fences to be signalled,
		 * or if we otherwise know that the moving fence has signalled,
		 * and we are certain the pages underneath are valid for
		 * immediate access (under normal operation), like just prior to
		 * binding the object or when setting up the CPU fault handler.
		 * See i915_gem_object_has_unknown_state();
		 */
		bool unknown_state;

		/**
		 * Priority list of potential placements for this object.
		 */
		struct intel_memory_region **placements;
		int n_placements;

		/**
		 * Memory region for this object.
		 */
		struct intel_memory_region *region;

		/**
		 * Memory manager resource allocated for this object. Only
		 * needed for the mock region.
		 */
		struct ttm_resource *res;

		/**
		 * Element within memory_region->objects or region->purgeable
		 * if the object is marked as DONTNEED. Access is protected by
		 * region->obj_lock.
		 */
		struct list_head region_link;

		struct i915_refct_sgt *rsgt;
		struct sg_table *pages;
		void *mapping;

		struct i915_page_sizes page_sizes;

		I915_SELFTEST_DECLARE(unsigned int page_mask);

		struct i915_gem_object_page_iter get_page;
		struct i915_gem_object_page_iter get_dma_page;

		/**
		 * Element within i915->mm.shrink_list or i915->mm.purge_list,
		 * locked by i915->mm.obj_lock.
		 */
		struct list_head link;

		/**
		 * Advice: are the backing pages purgeable?
		 */
		unsigned int madv:2;

		/**
		 * This is set if the object has been written to since the
		 * pages were last acquired.
		 */
		bool dirty:1;

		u32 tlb;
	} mm;

	struct {
		struct i915_refct_sgt *cached_io_rsgt;
		struct i915_gem_object_page_iter get_io_page;
		struct drm_i915_gem_object *backup;
		bool created:1;
	} ttm;

	/*
	 * Record which PXP key instance this object was created against (if
	 * any), so we can use it to determine if the encryption is valid by
	 * comparing against the current key instance.
	 */
	u32 pxp_key_instance;

	/** Record of address bit 17 of each page at last unbind. */
	unsigned long *bit_17;

	union {
#ifdef CONFIG_MMU_NOTIFIER
		struct i915_gem_userptr {
			uintptr_t ptr;
			unsigned long notifier_seq;

			struct mmu_interval_notifier notifier;
			struct page **pvec;
			int page_ref;
		} userptr;
#endif

		struct drm_mm_node *stolen;

		resource_size_t bo_offset;

		unsigned long scratch;
		u64 encode;

		void *gvt_info;
	};
};

static inline struct drm_i915_gem_object *
to_intel_bo(struct drm_gem_object *gem)
{
	/* Assert that to_intel_bo(NULL) == NULL */
	BUILD_BUG_ON(offsetof(struct drm_i915_gem_object, base));

	return container_of(gem, struct drm_i915_gem_object, base);
}

#endif