drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c - linux-mtk - Git at Google

 /*
  * Copyright 2012 Advanced Micro Devices, Inc.
  *
  * 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, sublicense,
  * 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 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 NONINFRINGEMENT.  IN NO EVENT SHALL
  * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) 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.
  *
  * based on nouveau_prime.c
  *
  * Authors: Alex Deucher
  */

 /**
  * DOC: PRIME Buffer Sharing
  *
  * The following callback implementations are used for :ref:`sharing GEM buffer
  * objects between different devices via PRIME <prime_buffer_sharing>`.
  */

 #include <drm/drmP.h>

 #include "amdgpu.h"
 #include "amdgpu_display.h"
 #include <drm/amdgpu_drm.h>
 #include <linux/dma-buf.h>
 #include <linux/dma-fence-array.h>

 static const struct dma_buf_ops amdgpu_dmabuf_ops;

 /**
  * amdgpu_gem_prime_get_sg_table - &drm_driver.gem_prime_get_sg_table
  * implementation
  * @obj: GEM buffer object
  *
  * Returns:
  * A scatter/gather table for the pinned pages of the buffer object's memory.
  */
 struct sg_table *amdgpu_gem_prime_get_sg_table(struct drm_gem_object *obj)
 {
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
 	int npages = bo->tbo.num_pages;

 	return drm_prime_pages_to_sg(bo->tbo.ttm->pages, npages);
 }

 /**
  * amdgpu_gem_prime_vmap - &dma_buf_ops.vmap implementation
  * @obj: GEM buffer object
  *
  * Sets up an in-kernel virtual mapping of the buffer object's memory.
  *
  * Returns:
  * The virtual address of the mapping or an error pointer.
  */
 void *amdgpu_gem_prime_vmap(struct drm_gem_object *obj)
 {
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
 	int ret;

 	ret = ttm_bo_kmap(&bo->tbo, 0, bo->tbo.num_pages,
 			  &bo->dma_buf_vmap);
 	if (ret)
 		return ERR_PTR(ret);

 	return bo->dma_buf_vmap.virtual;
 }

 /**
  * amdgpu_gem_prime_vunmap - &dma_buf_ops.vunmap implementation
  * @obj: GEM buffer object
  * @vaddr: virtual address (unused)
  *
  * Tears down the in-kernel virtual mapping of the buffer object's memory.
  */
 void amdgpu_gem_prime_vunmap(struct drm_gem_object *obj, void *vaddr)
 {
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);

 	ttm_bo_kunmap(&bo->dma_buf_vmap);
 }

 /**
  * amdgpu_gem_prime_mmap - &drm_driver.gem_prime_mmap implementation
  * @obj: GEM buffer object
  * @vma: virtual memory area
  *
  * Sets up a userspace mapping of the buffer object's memory in the given
  * virtual memory area.
  *
  * Returns:
  * 0 on success or negative error code.
  */
 int amdgpu_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
 {
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
 	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
 	unsigned asize = amdgpu_bo_size(bo);
 	int ret;

 	if (!vma->vm_file)
 		return -ENODEV;

 	if (adev == NULL)
 		return -ENODEV;

 	/* Check for valid size. */
 	if (asize < vma->vm_end - vma->vm_start)
 		return -EINVAL;

 	if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm) ||
 	    (bo->flags & AMDGPU_GEM_CREATE_NO_CPU_ACCESS)) {
 		return -EPERM;
 	}
 	vma->vm_pgoff += amdgpu_bo_mmap_offset(bo) >> PAGE_SHIFT;

 	/* prime mmap does not need to check access, so allow here */
 	ret = drm_vma_node_allow(&obj->vma_node, vma->vm_file->private_data);
 	if (ret)
 		return ret;

 	ret = ttm_bo_mmap(vma->vm_file, vma, &adev->mman.bdev);
 	drm_vma_node_revoke(&obj->vma_node, vma->vm_file->private_data);

 	return ret;
 }

 /**
  * amdgpu_gem_prime_import_sg_table - &drm_driver.gem_prime_import_sg_table
  * implementation
  * @dev: DRM device
  * @attach: DMA-buf attachment
  * @sg: Scatter/gather table
  *
  * Import shared DMA buffer memory exported by another device.
  *
  * Returns:
  * A new GEM buffer object of the given DRM device, representing the memory
  * described by the given DMA-buf attachment and scatter/gather table.
  */
 struct drm_gem_object *
 amdgpu_gem_prime_import_sg_table(struct drm_device *dev,
 				 struct dma_buf_attachment *attach,
 				 struct sg_table *sg)
 {
 	struct reservation_object *resv = attach->dmabuf->resv;
 	struct amdgpu_device *adev = dev->dev_private;
 	struct amdgpu_bo *bo;
 	struct amdgpu_bo_param bp;
 	int ret;

 	memset(&bp, 0, sizeof(bp));
 	bp.size = attach->dmabuf->size;
 	bp.byte_align = PAGE_SIZE;
 	bp.domain = AMDGPU_GEM_DOMAIN_CPU;
 	bp.flags = 0;
 	bp.type = ttm_bo_type_sg;
 	bp.resv = resv;
 	ww_mutex_lock(&resv->lock, NULL);
 	ret = amdgpu_bo_create(adev, &bp, &bo);
 	if (ret)
 		goto error;

 	bo->tbo.sg = sg;
 	bo->tbo.ttm->sg = sg;
 	bo->allowed_domains = AMDGPU_GEM_DOMAIN_GTT;
 	bo->preferred_domains = AMDGPU_GEM_DOMAIN_GTT;
 	if (attach->dmabuf->ops != &amdgpu_dmabuf_ops)
 		bo->prime_shared_count = 1;

 	ww_mutex_unlock(&resv->lock);
 	return &bo->gem_base;

 error:
 	ww_mutex_unlock(&resv->lock);
 	return ERR_PTR(ret);
 }

 static int
 __reservation_object_make_exclusive(struct reservation_object *obj)
 {
 	struct dma_fence **fences;
 	unsigned int count;
 	int r;

 	if (!reservation_object_get_list(obj)) /* no shared fences to convert */
 		return 0;

 	r = reservation_object_get_fences_rcu(obj, NULL, &count, &fences);
 	if (r)
 		return r;

 	if (count == 0) {
 		/* Now that was unexpected. */
 	} else if (count == 1) {
 		reservation_object_add_excl_fence(obj, fences[0]);
 		dma_fence_put(fences[0]);
 		kfree(fences);
 	} else {
 		struct dma_fence_array *array;

 		array = dma_fence_array_create(count, fences,
 					       dma_fence_context_alloc(1), 0,
 					       false);
 		if (!array)
 			goto err_fences_put;

 		reservation_object_add_excl_fence(obj, &array->base);
 		dma_fence_put(&array->base);
 	}

 	return 0;

 err_fences_put:
 	while (count--)
 		dma_fence_put(fences[count]);
 	kfree(fences);
 	return -ENOMEM;
 }

 /**
  * amdgpu_gem_map_attach - &dma_buf_ops.attach implementation
  * @dma_buf: shared DMA buffer
  * @attach: DMA-buf attachment
  *
  * Makes sure that the shared DMA buffer can be accessed by the target device.
  * For now, simply pins it to the GTT domain, where it should be accessible by
  * all DMA devices.
  *
  * Returns:
  * 0 on success or negative error code.
  */
 static int amdgpu_gem_map_attach(struct dma_buf *dma_buf,
 				 struct dma_buf_attachment *attach)
 {
 	struct drm_gem_object *obj = dma_buf->priv;
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
 	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
 	long r;

 	r = drm_gem_map_attach(dma_buf, attach);
 	if (r)
 		return r;

 	r = amdgpu_bo_reserve(bo, false);
 	if (unlikely(r != 0))
 		goto error_detach;


 	if (attach->dev->driver != adev->dev->driver) {
 		/*
 		 * We only create shared fences for internal use, but importers
 		 * of the dmabuf rely on exclusive fences for implicitly
 		 * tracking write hazards. As any of the current fences may
 		 * correspond to a write, we need to convert all existing
 		 * fences on the reservation object into a single exclusive
 		 * fence.
 		 */
 		r = __reservation_object_make_exclusive(bo->tbo.resv);
 		if (r)
 			goto error_unreserve;
 	}

 	/* pin buffer into GTT */
 	r = amdgpu_bo_pin(bo, AMDGPU_GEM_DOMAIN_GTT);
 	if (r)
 		goto error_unreserve;

 	if (attach->dev->driver != adev->dev->driver)
 		bo->prime_shared_count++;

 error_unreserve:
 	amdgpu_bo_unreserve(bo);

 error_detach:
 	if (r)
 		drm_gem_map_detach(dma_buf, attach);
 	return r;
 }

 /**
  * amdgpu_gem_map_detach - &dma_buf_ops.detach implementation
  * @dma_buf: shared DMA buffer
  * @attach: DMA-buf attachment
  *
  * This is called when a shared DMA buffer no longer needs to be accessible by
  * the other device. For now, simply unpins the buffer from GTT.
  */
 static void amdgpu_gem_map_detach(struct dma_buf *dma_buf,
 				  struct dma_buf_attachment *attach)
 {
 	struct drm_gem_object *obj = dma_buf->priv;
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
 	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
 	int ret = 0;

 	ret = amdgpu_bo_reserve(bo, true);
 	if (unlikely(ret != 0))
 		goto error;

 	amdgpu_bo_unpin(bo);
 	if (attach->dev->driver != adev->dev->driver && bo->prime_shared_count)
 		bo->prime_shared_count--;
 	amdgpu_bo_unreserve(bo);

 error:
 	drm_gem_map_detach(dma_buf, attach);
 }

 /**
  * amdgpu_gem_prime_res_obj - &drm_driver.gem_prime_res_obj implementation
  * @obj: GEM buffer object
  *
  * Returns:
  * The buffer object's reservation object.
  */
 struct reservation_object *amdgpu_gem_prime_res_obj(struct drm_gem_object *obj)
 {
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);

 	return bo->tbo.resv;
 }

 /**
  * amdgpu_gem_begin_cpu_access - &dma_buf_ops.begin_cpu_access implementation
  * @dma_buf: shared DMA buffer
  * @direction: direction of DMA transfer
  *
  * This is called before CPU access to the shared DMA buffer's memory. If it's
  * a read access, the buffer is moved to the GTT domain if possible, for optimal
  * CPU read performance.
  *
  * Returns:
  * 0 on success or negative error code.
  */
 static int amdgpu_gem_begin_cpu_access(struct dma_buf *dma_buf,
 				       enum dma_data_direction direction)
 {
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(dma_buf->priv);
 	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
 	struct ttm_operation_ctx ctx = { true, false };
 	u32 domain = amdgpu_display_supported_domains(adev);
 	int ret;
 	bool reads = (direction == DMA_BIDIRECTIONAL ||
 		      direction == DMA_FROM_DEVICE);

 	if (!reads || !(domain & AMDGPU_GEM_DOMAIN_GTT))
 		return 0;

 	/* move to gtt */
 	ret = amdgpu_bo_reserve(bo, false);
 	if (unlikely(ret != 0))
 		return ret;

 	if (!bo->pin_count && (bo->allowed_domains & AMDGPU_GEM_DOMAIN_GTT)) {
 		amdgpu_bo_placement_from_domain(bo, AMDGPU_GEM_DOMAIN_GTT);
 		ret = ttm_bo_validate(&bo->tbo, &bo->placement, &ctx);
 	}

 	amdgpu_bo_unreserve(bo);
 	return ret;
 }

 static const struct dma_buf_ops amdgpu_dmabuf_ops = {
 	.attach = amdgpu_gem_map_attach,
 	.detach = amdgpu_gem_map_detach,
 	.map_dma_buf = drm_gem_map_dma_buf,
 	.unmap_dma_buf = drm_gem_unmap_dma_buf,
 	.release = drm_gem_dmabuf_release,
 	.begin_cpu_access = amdgpu_gem_begin_cpu_access,
 	.map = drm_gem_dmabuf_kmap,
 	.unmap = drm_gem_dmabuf_kunmap,
 	.mmap = drm_gem_dmabuf_mmap,
 	.vmap = drm_gem_dmabuf_vmap,
 	.vunmap = drm_gem_dmabuf_vunmap,
 };

 /**
  * amdgpu_gem_prime_export - &drm_driver.gem_prime_export implementation
  * @dev: DRM device
  * @gobj: GEM buffer object
  * @flags: flags like DRM_CLOEXEC and DRM_RDWR
  *
  * The main work is done by the &drm_gem_prime_export helper, which in turn
  * uses &amdgpu_gem_prime_res_obj.
  *
  * Returns:
  * Shared DMA buffer representing the GEM buffer object from the given device.
  */
 struct dma_buf *amdgpu_gem_prime_export(struct drm_device *dev,
 					struct drm_gem_object *gobj,
 					int flags)
 {
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(gobj);
 	struct dma_buf *buf;

 	if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm) ||
 	    bo->flags & AMDGPU_GEM_CREATE_VM_ALWAYS_VALID)
 		return ERR_PTR(-EPERM);

 	buf = drm_gem_prime_export(dev, gobj, flags);
 	if (!IS_ERR(buf)) {
 		buf->file->f_mapping = dev->anon_inode->i_mapping;
 		buf->ops = &amdgpu_dmabuf_ops;
 	}

 	return buf;
 }

 /**
  * amdgpu_gem_prime_import - &drm_driver.gem_prime_import implementation
  * @dev: DRM device
  * @dma_buf: Shared DMA buffer
  *
  * The main work is done by the &drm_gem_prime_import helper, which in turn
  * uses &amdgpu_gem_prime_import_sg_table.
  *
  * Returns:
  * GEM buffer object representing the shared DMA buffer for the given device.
  */
 struct drm_gem_object *amdgpu_gem_prime_import(struct drm_device *dev,
 					    struct dma_buf *dma_buf)
 {
 	struct drm_gem_object *obj;

 	if (dma_buf->ops == &amdgpu_dmabuf_ops) {
 		obj = dma_buf->priv;
 		if (obj->dev == dev) {
 			/*
 			 * Importing dmabuf exported from out own gem increases
 			 * refcount on gem itself instead of f_count of dmabuf.
 			 */
 			drm_gem_object_get(obj);
 			return obj;
 		}
 	}

 	return drm_gem_prime_import(dev, dma_buf);
 }
	/*
	* Copyright 2012 Advanced Micro Devices, Inc.
	*
	* 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, sublicense,
	* 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 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 NONINFRINGEMENT. IN NO EVENT SHALL
	* THE COPYRIGHT HOLDER(S) OR AUTHOR(S) 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.
	*
	* based on nouveau_prime.c
	*
	* Authors: Alex Deucher
	*/

	/**
	* DOC: PRIME Buffer Sharing
	*
	* The following callback implementations are used for :ref:`sharing GEM buffer
	* objects between different devices via PRIME <prime_buffer_sharing>`.
	*/

	#include <drm/drmP.h>

	#include "amdgpu.h"
	#include "amdgpu_display.h"
	#include <drm/amdgpu_drm.h>
	#include <linux/dma-buf.h>
	#include <linux/dma-fence-array.h>

	static const struct dma_buf_ops amdgpu_dmabuf_ops;

	/**
	* amdgpu_gem_prime_get_sg_table - &drm_driver.gem_prime_get_sg_table
	* implementation
	* @obj: GEM buffer object
	*
	* Returns:
	* A scatter/gather table for the pinned pages of the buffer object's memory.
	*/
	struct sg_table amdgpu_gem_prime_get_sg_table(struct drm_gem_object obj)
	{
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
	int npages = bo->tbo.num_pages;

	return drm_prime_pages_to_sg(bo->tbo.ttm->pages, npages);
	}

	/**
	* amdgpu_gem_prime_vmap - &dma_buf_ops.vmap implementation
	* @obj: GEM buffer object
	*
	* Sets up an in-kernel virtual mapping of the buffer object's memory.
	*
	* Returns:
	* The virtual address of the mapping or an error pointer.
	*/
	void amdgpu_gem_prime_vmap(struct drm_gem_object obj)
	{
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
	int ret;

	ret = ttm_bo_kmap(&bo->tbo, 0, bo->tbo.num_pages,
	&bo->dma_buf_vmap);
	if (ret)
	return ERR_PTR(ret);

	return bo->dma_buf_vmap.virtual;
	}

	/**
	* amdgpu_gem_prime_vunmap - &dma_buf_ops.vunmap implementation
	* @obj: GEM buffer object
	* @vaddr: virtual address (unused)
	*
	* Tears down the in-kernel virtual mapping of the buffer object's memory.
	*/
	void amdgpu_gem_prime_vunmap(struct drm_gem_object obj, void vaddr)
	{
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);

	ttm_bo_kunmap(&bo->dma_buf_vmap);
	}

	/**
	* amdgpu_gem_prime_mmap - &drm_driver.gem_prime_mmap implementation
	* @obj: GEM buffer object
	* @vma: virtual memory area
	*
	* Sets up a userspace mapping of the buffer object's memory in the given
	* virtual memory area.
	*
	* Returns:
	* 0 on success or negative error code.
	*/
	int amdgpu_gem_prime_mmap(struct drm_gem_object obj, struct vm_area_struct vma)
	{
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
	unsigned asize = amdgpu_bo_size(bo);
	int ret;

	if (!vma->vm_file)
	return -ENODEV;

	if (adev == NULL)
	return -ENODEV;

	/* Check for valid size. */
	if (asize < vma->vm_end - vma->vm_start)
	return -EINVAL;

	if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm) \|\|
	(bo->flags & AMDGPU_GEM_CREATE_NO_CPU_ACCESS)) {
	return -EPERM;
	}
	vma->vm_pgoff += amdgpu_bo_mmap_offset(bo) >> PAGE_SHIFT;

	/* prime mmap does not need to check access, so allow here */
	ret = drm_vma_node_allow(&obj->vma_node, vma->vm_file->private_data);
	if (ret)
	return ret;

	ret = ttm_bo_mmap(vma->vm_file, vma, &adev->mman.bdev);
	drm_vma_node_revoke(&obj->vma_node, vma->vm_file->private_data);

	return ret;
	}

	/**
	* amdgpu_gem_prime_import_sg_table - &drm_driver.gem_prime_import_sg_table
	* implementation
	* @dev: DRM device
	* @attach: DMA-buf attachment
	* @sg: Scatter/gather table
	*
	* Import shared DMA buffer memory exported by another device.
	*
	* Returns:
	* A new GEM buffer object of the given DRM device, representing the memory
	* described by the given DMA-buf attachment and scatter/gather table.
	*/
	struct drm_gem_object *
	amdgpu_gem_prime_import_sg_table(struct drm_device *dev,
	struct dma_buf_attachment *attach,
	struct sg_table *sg)
	{
	struct reservation_object *resv = attach->dmabuf->resv;
	struct amdgpu_device *adev = dev->dev_private;
	struct amdgpu_bo *bo;
	struct amdgpu_bo_param bp;
	int ret;

	memset(&bp, 0, sizeof(bp));
	bp.size = attach->dmabuf->size;
	bp.byte_align = PAGE_SIZE;
	bp.domain = AMDGPU_GEM_DOMAIN_CPU;
	bp.flags = 0;
	bp.type = ttm_bo_type_sg;
	bp.resv = resv;
	ww_mutex_lock(&resv->lock, NULL);
	ret = amdgpu_bo_create(adev, &bp, &bo);
	if (ret)
	goto error;

	bo->tbo.sg = sg;
	bo->tbo.ttm->sg = sg;
	bo->allowed_domains = AMDGPU_GEM_DOMAIN_GTT;
	bo->preferred_domains = AMDGPU_GEM_DOMAIN_GTT;
	if (attach->dmabuf->ops != &amdgpu_dmabuf_ops)
	bo->prime_shared_count = 1;

	ww_mutex_unlock(&resv->lock);
	return &bo->gem_base;

	error:
	ww_mutex_unlock(&resv->lock);
	return ERR_PTR(ret);
	}

	static int
	__reservation_object_make_exclusive(struct reservation_object *obj)
	{
	struct dma_fence **fences;
	unsigned int count;
	int r;

	if (!reservation_object_get_list(obj)) /* no shared fences to convert */
	return 0;

	r = reservation_object_get_fences_rcu(obj, NULL, &count, &fences);
	if (r)
	return r;

	if (count == 0) {
	/* Now that was unexpected. */
	} else if (count == 1) {
	reservation_object_add_excl_fence(obj, fences[0]);
	dma_fence_put(fences[0]);
	kfree(fences);
	} else {
	struct dma_fence_array *array;

	array = dma_fence_array_create(count, fences,
	dma_fence_context_alloc(1), 0,
	false);
	if (!array)
	goto err_fences_put;

	reservation_object_add_excl_fence(obj, &array->base);
	dma_fence_put(&array->base);
	}

	return 0;

	err_fences_put:
	while (count--)
	dma_fence_put(fences[count]);
	kfree(fences);
	return -ENOMEM;
	}

	/**
	* amdgpu_gem_map_attach - &dma_buf_ops.attach implementation
	* @dma_buf: shared DMA buffer
	* @attach: DMA-buf attachment
	*
	* Makes sure that the shared DMA buffer can be accessed by the target device.
	* For now, simply pins it to the GTT domain, where it should be accessible by
	* all DMA devices.
	*
	* Returns:
	* 0 on success or negative error code.
	*/
	static int amdgpu_gem_map_attach(struct dma_buf *dma_buf,
	struct dma_buf_attachment *attach)
	{
	struct drm_gem_object *obj = dma_buf->priv;
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
	long r;

	r = drm_gem_map_attach(dma_buf, attach);
	if (r)
	return r;

	r = amdgpu_bo_reserve(bo, false);
	if (unlikely(r != 0))
	goto error_detach;


	if (attach->dev->driver != adev->dev->driver) {
	/*
	* We only create shared fences for internal use, but importers
	* of the dmabuf rely on exclusive fences for implicitly
	* tracking write hazards. As any of the current fences may
	* correspond to a write, we need to convert all existing
	* fences on the reservation object into a single exclusive
	* fence.
	*/
	r = __reservation_object_make_exclusive(bo->tbo.resv);
	if (r)
	goto error_unreserve;
	}

	/* pin buffer into GTT */
	r = amdgpu_bo_pin(bo, AMDGPU_GEM_DOMAIN_GTT);
	if (r)
	goto error_unreserve;

	if (attach->dev->driver != adev->dev->driver)
	bo->prime_shared_count++;

	error_unreserve:
	amdgpu_bo_unreserve(bo);

	error_detach:
	if (r)
	drm_gem_map_detach(dma_buf, attach);
	return r;
	}

	/**
	* amdgpu_gem_map_detach - &dma_buf_ops.detach implementation
	* @dma_buf: shared DMA buffer
	* @attach: DMA-buf attachment
	*
	* This is called when a shared DMA buffer no longer needs to be accessible by
	* the other device. For now, simply unpins the buffer from GTT.
	*/
	static void amdgpu_gem_map_detach(struct dma_buf *dma_buf,
	struct dma_buf_attachment *attach)
	{
	struct drm_gem_object *obj = dma_buf->priv;
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
	int ret = 0;

	ret = amdgpu_bo_reserve(bo, true);
	if (unlikely(ret != 0))
	goto error;

	amdgpu_bo_unpin(bo);
	if (attach->dev->driver != adev->dev->driver && bo->prime_shared_count)
	bo->prime_shared_count--;
	amdgpu_bo_unreserve(bo);

	error:
	drm_gem_map_detach(dma_buf, attach);
	}

	/**
	* amdgpu_gem_prime_res_obj - &drm_driver.gem_prime_res_obj implementation
	* @obj: GEM buffer object
	*
	* Returns:
	* The buffer object's reservation object.
	*/
	struct reservation_object amdgpu_gem_prime_res_obj(struct drm_gem_object obj)
	{
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);

	return bo->tbo.resv;
	}

	/**
	* amdgpu_gem_begin_cpu_access - &dma_buf_ops.begin_cpu_access implementation
	* @dma_buf: shared DMA buffer
	* @direction: direction of DMA transfer
	*
	* This is called before CPU access to the shared DMA buffer's memory. If it's
	* a read access, the buffer is moved to the GTT domain if possible, for optimal
	* CPU read performance.
	*
	* Returns:
	* 0 on success or negative error code.
	*/
	static int amdgpu_gem_begin_cpu_access(struct dma_buf *dma_buf,
	enum dma_data_direction direction)
	{
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(dma_buf->priv);
	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
	struct ttm_operation_ctx ctx = { true, false };
	u32 domain = amdgpu_display_supported_domains(adev);
	int ret;
	bool reads = (direction == DMA_BIDIRECTIONAL \|\|
	direction == DMA_FROM_DEVICE);

	if (!reads \|\| !(domain & AMDGPU_GEM_DOMAIN_GTT))
	return 0;

	/* move to gtt */
	ret = amdgpu_bo_reserve(bo, false);
	if (unlikely(ret != 0))
	return ret;

	if (!bo->pin_count && (bo->allowed_domains & AMDGPU_GEM_DOMAIN_GTT)) {
	amdgpu_bo_placement_from_domain(bo, AMDGPU_GEM_DOMAIN_GTT);
	ret = ttm_bo_validate(&bo->tbo, &bo->placement, &ctx);
	}

	amdgpu_bo_unreserve(bo);
	return ret;
	}

	static const struct dma_buf_ops amdgpu_dmabuf_ops = {
	.attach = amdgpu_gem_map_attach,
	.detach = amdgpu_gem_map_detach,
	.map_dma_buf = drm_gem_map_dma_buf,
	.unmap_dma_buf = drm_gem_unmap_dma_buf,
	.release = drm_gem_dmabuf_release,
	.begin_cpu_access = amdgpu_gem_begin_cpu_access,
	.map = drm_gem_dmabuf_kmap,
	.unmap = drm_gem_dmabuf_kunmap,
	.mmap = drm_gem_dmabuf_mmap,
	.vmap = drm_gem_dmabuf_vmap,
	.vunmap = drm_gem_dmabuf_vunmap,
	};

	/**
	* amdgpu_gem_prime_export - &drm_driver.gem_prime_export implementation
	* @dev: DRM device
	* @gobj: GEM buffer object
	* @flags: flags like DRM_CLOEXEC and DRM_RDWR
	*
	* The main work is done by the &drm_gem_prime_export helper, which in turn
	* uses &amdgpu_gem_prime_res_obj.
	*
	* Returns:
	* Shared DMA buffer representing the GEM buffer object from the given device.
	*/
	struct dma_buf amdgpu_gem_prime_export(struct drm_device dev,
	struct drm_gem_object *gobj,
	int flags)
	{
	struct amdgpu_bo *bo = gem_to_amdgpu_bo(gobj);
	struct dma_buf *buf;

	if (amdgpu_ttm_tt_get_usermm(bo->tbo.ttm) \|\|
	bo->flags & AMDGPU_GEM_CREATE_VM_ALWAYS_VALID)
	return ERR_PTR(-EPERM);

	buf = drm_gem_prime_export(dev, gobj, flags);
	if (!IS_ERR(buf)) {
	buf->file->f_mapping = dev->anon_inode->i_mapping;
	buf->ops = &amdgpu_dmabuf_ops;
	}

	return buf;
	}

	/**
	* amdgpu_gem_prime_import - &drm_driver.gem_prime_import implementation
	* @dev: DRM device
	* @dma_buf: Shared DMA buffer
	*
	* The main work is done by the &drm_gem_prime_import helper, which in turn
	* uses &amdgpu_gem_prime_import_sg_table.
	*
	* Returns:
	* GEM buffer object representing the shared DMA buffer for the given device.
	*/
	struct drm_gem_object amdgpu_gem_prime_import(struct drm_device dev,
	struct dma_buf *dma_buf)
	{
	struct drm_gem_object *obj;

	if (dma_buf->ops == &amdgpu_dmabuf_ops) {
	obj = dma_buf->priv;
	if (obj->dev == dev) {
	/*
	* Importing dmabuf exported from out own gem increases
	* refcount on gem itself instead of f_count of dmabuf.
	*/
	drm_gem_object_get(obj);
	return obj;
	}
	}

	return drm_gem_prime_import(dev, dma_buf);
	}