// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright 2018 Noralf Trønnes
 */

#include <linux/dma-buf.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/shmem_fs.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>

#include <drm/drm.h>
#include <drm/drm_device.h>
#include <drm/drm_drv.h>
#include <drm/drm_gem_shmem_helper.h>
#include <drm/drm_prime.h>
#include <drm/drm_print.h>

/**
 * DOC: overview
 *
 * This library provides helpers for GEM objects backed by shmem buffers
 * allocated using anonymous pageable memory.
 */

static const struct drm_gem_object_funcs drm_gem_shmem_funcs = {
        .free = drm_gem_shmem_free_object,
        .print_info = drm_gem_shmem_print_info,
        .pin = drm_gem_shmem_pin,
        .unpin = drm_gem_shmem_unpin,
        .get_sg_table = drm_gem_shmem_get_sg_table,
        .vmap = drm_gem_shmem_vmap,
        .vunmap = drm_gem_shmem_vunmap,
        .mmap = drm_gem_shmem_mmap,
};

static struct drm_gem_shmem_object *
__drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private)
{
        struct drm_gem_shmem_object *shmem;
        struct drm_gem_object *obj;
        int ret = 0;

        size = PAGE_ALIGN(size);

        if (dev->driver->gem_create_object)
                obj = dev->driver->gem_create_object(dev, size);
        else
                obj = kzalloc(sizeof(*shmem), GFP_KERNEL);
        if (!obj)
                return ERR_PTR(-ENOMEM);

        shmem = to_drm_gem_shmem_obj(obj);

        if (!obj->funcs)
                obj->funcs = &drm_gem_shmem_funcs;

        if (private) {
                drm_gem_private_object_init(dev, obj, size);
                shmem->map_wc = false; /* dma-buf mappings use always writecombine */
        } else {
                ret = drm_gem_object_init(dev, obj, size);
        }
        if (ret)
                goto err_free;

        ret = drm_gem_create_mmap_offset(obj);
        if (ret)
                goto err_release;

        mutex_init(&shmem->pages_lock);
        mutex_init(&shmem->vmap_lock);
        INIT_LIST_HEAD(&shmem->madv_list);

        if (!private) {
                /*
                 * Our buffers are kept pinned, so allocating them
                 * from the MOVABLE zone is a really bad idea, and
                 * conflicts with CMA. See comments above new_inode()
                 * why this is required _and_ expected if you're
                 * going to pin these pages.
                 */
                mapping_set_gfp_mask(obj->filp->f_mapping, GFP_HIGHUSER |
                                     __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
        }

        return shmem;

err_release:
        drm_gem_object_release(obj);
err_free:
        kfree(obj);

        return ERR_PTR(ret);
}
/**
 * drm_gem_shmem_create - Allocate an object with the given size
 * @dev: DRM device
 * @size: Size of the object to allocate
 *
 * This function creates a shmem GEM object.
 *
 * Returns:
 * A struct drm_gem_shmem_object * on success or an ERR_PTR()-encoded negative
 * error code on failure.
 */
struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size)
{
        return __drm_gem_shmem_create(dev, size, false);
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_create);

/**
 * drm_gem_shmem_free_object - Free resources associated with a shmem GEM object
 * @obj: GEM object to free
 *
 * This function cleans up the GEM object state and frees the memory used to
 * store the object itself. It should be used to implement
 * &drm_gem_object_funcs.free.
 */
void drm_gem_shmem_free_object(struct drm_gem_object *obj)
{
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        WARN_ON(shmem->vmap_use_count);

        if (obj->import_attach) {
                drm_prime_gem_destroy(obj, shmem->sgt);
        } else {
                if (shmem->sgt) {
                        dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
                                          DMA_BIDIRECTIONAL, 0);
                        sg_free_table(shmem->sgt);
                        kfree(shmem->sgt);
                }
                if (shmem->pages)
                        drm_gem_shmem_put_pages(shmem);
        }

        WARN_ON(shmem->pages_use_count);

        drm_gem_object_release(obj);
        mutex_destroy(&shmem->pages_lock);
        mutex_destroy(&shmem->vmap_lock);
        kfree(shmem);
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_free_object);

static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
{
        struct drm_gem_object *obj = &shmem->base;
        struct page **pages;

        if (shmem->pages_use_count++ > 0)
                return 0;

        pages = drm_gem_get_pages(obj);
        if (IS_ERR(pages)) {
                DRM_DEBUG_KMS("Failed to get pages (%ld)\n", PTR_ERR(pages));
                shmem->pages_use_count = 0;
                return PTR_ERR(pages);
        }

        shmem->pages = pages;

        return 0;
}

/*
 * drm_gem_shmem_get_pages - Allocate backing pages for a shmem GEM object
 * @shmem: shmem GEM object
 *
 * This function makes sure that backing pages exists for the shmem GEM object
 * and increases the use count.
 *
 * Returns:
 * 0 on success or a negative error code on failure.
 */
int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
{
        int ret;

        WARN_ON(shmem->base.import_attach);

        ret = mutex_lock_interruptible(&shmem->pages_lock);
        if (ret)
                return ret;
        ret = drm_gem_shmem_get_pages_locked(shmem);
        mutex_unlock(&shmem->pages_lock);

        return ret;
}
EXPORT_SYMBOL(drm_gem_shmem_get_pages);

static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
{
        struct drm_gem_object *obj = &shmem->base;

        if (WARN_ON_ONCE(!shmem->pages_use_count))
                return;

        if (--shmem->pages_use_count > 0)
                return;

        drm_gem_put_pages(obj, shmem->pages,
                          shmem->pages_mark_dirty_on_put,
                          shmem->pages_mark_accessed_on_put);
        shmem->pages = NULL;
}

/*
 * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
 * @shmem: shmem GEM object
 *
 * This function decreases the use count and puts the backing pages when use drops to zero.
 */
void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
{
        mutex_lock(&shmem->pages_lock);
        drm_gem_shmem_put_pages_locked(shmem);
        mutex_unlock(&shmem->pages_lock);
}
EXPORT_SYMBOL(drm_gem_shmem_put_pages);

/**
 * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
 * @obj: GEM object
 *
 * This function makes sure the backing pages are pinned in memory while the
 * buffer is exported. It should only be used to implement
 * &drm_gem_object_funcs.pin.
 *
 * Returns:
 * 0 on success or a negative error code on failure.
 */
int drm_gem_shmem_pin(struct drm_gem_object *obj)
{
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        WARN_ON(shmem->base.import_attach);

        return drm_gem_shmem_get_pages(shmem);
}
EXPORT_SYMBOL(drm_gem_shmem_pin);

/**
 * drm_gem_shmem_unpin - Unpin backing pages for a shmem GEM object
 * @obj: GEM object
 *
 * This function removes the requirement that the backing pages are pinned in
 * memory. It should only be used to implement &drm_gem_object_funcs.unpin.
 */
void drm_gem_shmem_unpin(struct drm_gem_object *obj)
{
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        WARN_ON(shmem->base.import_attach);

        drm_gem_shmem_put_pages(shmem);
}
EXPORT_SYMBOL(drm_gem_shmem_unpin);

static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem, struct dma_buf_map *map)
{
        struct drm_gem_object *obj = &shmem->base;
        int ret = 0;

        if (shmem->vmap_use_count++ > 0) {
                dma_buf_map_set_vaddr(map, shmem->vaddr);
                return 0;
        }

        if (obj->import_attach) {
                ret = dma_buf_vmap(obj->import_attach->dmabuf, map);
                if (!ret) {
                        if (WARN_ON(map->is_iomem)) {
                                ret = -EIO;
                                goto err_put_pages;
                        }
                        shmem->vaddr = map->vaddr;
                }
        } else {
                pgprot_t prot = PAGE_KERNEL;

                ret = drm_gem_shmem_get_pages(shmem);
                if (ret)
                        goto err_zero_use;

                if (shmem->map_wc)
                        prot = pgprot_writecombine(prot);
                shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
                                    VM_MAP, prot);
                if (!shmem->vaddr)
                        ret = -ENOMEM;
                else
                        dma_buf_map_set_vaddr(map, shmem->vaddr);
        }

        if (ret) {
                DRM_DEBUG_KMS("Failed to vmap pages, error %d\n", ret);
                goto err_put_pages;
        }

        return 0;

err_put_pages:
        if (!obj->import_attach)
                drm_gem_shmem_put_pages(shmem);
err_zero_use:
        shmem->vmap_use_count = 0;

        return ret;
}

/*
 * drm_gem_shmem_vmap - Create a virtual mapping for a shmem GEM object
 * @shmem: shmem GEM object
 * @map: Returns the kernel virtual address of the SHMEM GEM object's backing
 *       store.
 *
 * This function makes sure that a contiguous kernel virtual address mapping
 * exists for the buffer backing the shmem GEM object.
 *
 * This function can be used to implement &drm_gem_object_funcs.vmap. But it can
 * also be called by drivers directly, in which case it will hide the
 * differences between dma-buf imported and natively allocated objects.
 *
 * Acquired mappings should be cleaned up by calling drm_gem_shmem_vunmap().
 *
 * Returns:
 * 0 on success or a negative error code on failure.
 */
int drm_gem_shmem_vmap(struct drm_gem_object *obj, struct dma_buf_map *map)
{
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
        int ret;

        ret = mutex_lock_interruptible(&shmem->vmap_lock);
        if (ret)
                return ret;
        ret = drm_gem_shmem_vmap_locked(shmem, map);
        mutex_unlock(&shmem->vmap_lock);

        return ret;
}
EXPORT_SYMBOL(drm_gem_shmem_vmap);

static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
                                        struct dma_buf_map *map)
{
        struct drm_gem_object *obj = &shmem->base;

        if (WARN_ON_ONCE(!shmem->vmap_use_count))
                return;

        if (--shmem->vmap_use_count > 0)
                return;

        if (obj->import_attach) {
                dma_buf_vunmap(obj->import_attach->dmabuf, map);
        } else {
                vunmap(shmem->vaddr);
                drm_gem_shmem_put_pages(shmem);
        }

        shmem->vaddr = NULL;
}

/*
 * drm_gem_shmem_vunmap - Unmap a virtual mapping for a shmem GEM object
 * @shmem: shmem GEM object
 * @map: Kernel virtual address where the SHMEM GEM object was mapped
 *
 * This function cleans up a kernel virtual address mapping acquired by
 * drm_gem_shmem_vmap(). The mapping is only removed when the use count drops to
 * zero.
 *
 * This function can be used to implement &drm_gem_object_funcs.vmap. But it can
 * also be called by drivers directly, in which case it will hide the
 * differences between dma-buf imported and natively allocated objects.
 */
void drm_gem_shmem_vunmap(struct drm_gem_object *obj, struct dma_buf_map *map)
{
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        mutex_lock(&shmem->vmap_lock);
        drm_gem_shmem_vunmap_locked(shmem, map);
        mutex_unlock(&shmem->vmap_lock);
}
EXPORT_SYMBOL(drm_gem_shmem_vunmap);

struct drm_gem_shmem_object *
drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
                                 struct drm_device *dev, size_t size,
                                 uint32_t *handle)
{
        struct drm_gem_shmem_object *shmem;
        int ret;

        shmem = drm_gem_shmem_create(dev, size);
        if (IS_ERR(shmem))
                return shmem;

        /*
         * Allocate an id of idr table where the obj is registered
         * and handle has the id what user can see.
         */
        ret = drm_gem_handle_create(file_priv, &shmem->base, handle);
        /* drop reference from allocate - handle holds it now. */
        drm_gem_object_put(&shmem->base);
        if (ret)
                return ERR_PTR(ret);

        return shmem;
}
EXPORT_SYMBOL(drm_gem_shmem_create_with_handle);

/* Update madvise status, returns true if not purged, else
 * false or -errno.
 */
int drm_gem_shmem_madvise(struct drm_gem_object *obj, int madv)
{
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        mutex_lock(&shmem->pages_lock);

        if (shmem->madv >= 0)
                shmem->madv = madv;

        madv = shmem->madv;

        mutex_unlock(&shmem->pages_lock);

        return (madv >= 0);
}
EXPORT_SYMBOL(drm_gem_shmem_madvise);

void drm_gem_shmem_purge_locked(struct drm_gem_object *obj)
{
        struct drm_device *dev = obj->dev;
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        WARN_ON(!drm_gem_shmem_is_purgeable(shmem));

        dma_unmap_sgtable(obj->dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);
        sg_free_table(shmem->sgt);
        kfree(shmem->sgt);
        shmem->sgt = NULL;

        drm_gem_shmem_put_pages_locked(shmem);

        shmem->madv = -1;

        drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
        drm_gem_free_mmap_offset(obj);

        /* Our goal here is to return as much of the memory as
         * is possible back to the system as we are called from OOM.
         * To do this we must instruct the shmfs to drop all of its
         * backing pages, *now*.
         */
        shmem_truncate_range(file_inode(obj->filp), 0, (loff_t)-1);

        invalidate_mapping_pages(file_inode(obj->filp)->i_mapping,
                        0, (loff_t)-1);
}
EXPORT_SYMBOL(drm_gem_shmem_purge_locked);

bool drm_gem_shmem_purge(struct drm_gem_object *obj)
{
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        if (!mutex_trylock(&shmem->pages_lock))
                return false;
        drm_gem_shmem_purge_locked(obj);
        mutex_unlock(&shmem->pages_lock);

        return true;
}
EXPORT_SYMBOL(drm_gem_shmem_purge);

/**
 * drm_gem_shmem_dumb_create - Create a dumb shmem buffer object
 * @file: DRM file structure to create the dumb buffer for
 * @dev: DRM device
 * @args: IOCTL data
 *
 * This function computes the pitch of the dumb buffer and rounds it up to an
 * integer number of bytes per pixel. Drivers for hardware that doesn't have
 * any additional restrictions on the pitch can directly use this function as
 * their &drm_driver.dumb_create callback.
 *
 * For hardware with additional restrictions, drivers can adjust the fields
 * set up by userspace before calling into this function.
 *
 * Returns:
 * 0 on success or a negative error code on failure.
 */
int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
                              struct drm_mode_create_dumb *args)
{
        u32 min_pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
        struct drm_gem_shmem_object *shmem;

        if (!args->pitch || !args->size) {
                args->pitch = min_pitch;
                args->size = PAGE_ALIGN(args->pitch * args->height);
        } else {
                /* ensure sane minimum values */
                if (args->pitch < min_pitch)
                        args->pitch = min_pitch;
                if (args->size < args->pitch * args->height)
                        args->size = PAGE_ALIGN(args->pitch * args->height);
        }

        shmem = drm_gem_shmem_create_with_handle(file, dev, args->size, &args->handle);

        return PTR_ERR_OR_ZERO(shmem);
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create);

static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        struct drm_gem_object *obj = vma->vm_private_data;
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
        loff_t num_pages = obj->size >> PAGE_SHIFT;
        vm_fault_t ret;
        struct page *page;
        pgoff_t page_offset;

        /* We don't use vmf->pgoff since that has the fake offset */
        page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;

        mutex_lock(&shmem->pages_lock);

        if (page_offset >= num_pages ||
            WARN_ON_ONCE(!shmem->pages) ||
            shmem->madv < 0) {
                ret = VM_FAULT_SIGBUS;
        } else {
                page = shmem->pages[page_offset];

                ret = vmf_insert_page(vma, vmf->address, page);
        }

        mutex_unlock(&shmem->pages_lock);

        return ret;
}

static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
{
        struct drm_gem_object *obj = vma->vm_private_data;
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
        int ret;

        WARN_ON(shmem->base.import_attach);

        ret = drm_gem_shmem_get_pages(shmem);
        WARN_ON_ONCE(ret != 0);

        drm_gem_vm_open(vma);
}

static void drm_gem_shmem_vm_close(struct vm_area_struct *vma)
{
        struct drm_gem_object *obj = vma->vm_private_data;
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        drm_gem_shmem_put_pages(shmem);
        drm_gem_vm_close(vma);
}

static const struct vm_operations_struct drm_gem_shmem_vm_ops = {
        .fault = drm_gem_shmem_fault,
        .open = drm_gem_shmem_vm_open,
        .close = drm_gem_shmem_vm_close,
};

/**
 * drm_gem_shmem_mmap - Memory-map a shmem GEM object
 * @obj: gem object
 * @vma: VMA for the area to be mapped
 *
 * This function implements an augmented version of the GEM DRM file mmap
 * operation for shmem objects. Drivers which employ the shmem helpers should
 * use this function as their &drm_gem_object_funcs.mmap handler.
 *
 * Returns:
 * 0 on success or a negative error code on failure.
 */
int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
{
        struct drm_gem_shmem_object *shmem;
        int ret;

        if (obj->import_attach) {
                /* Drop the reference drm_gem_mmap_obj() acquired.*/
                drm_gem_object_put(obj);
                vma->vm_private_data = NULL;

                return dma_buf_mmap(obj->dma_buf, vma, 0);
        }

        shmem = to_drm_gem_shmem_obj(obj);

        ret = drm_gem_shmem_get_pages(shmem);
        if (ret) {
                drm_gem_vm_close(vma);
                return ret;
        }

        vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;
        vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
        if (shmem->map_wc)
                vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
        vma->vm_ops = &drm_gem_shmem_vm_ops;

        return 0;
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_mmap);

/**
 * drm_gem_shmem_print_info() - Print &drm_gem_shmem_object info for debugfs
 * @p: DRM printer
 * @indent: Tab indentation level
 * @obj: GEM object
 *
 * This implements the &drm_gem_object_funcs.info callback.
 */
void drm_gem_shmem_print_info(struct drm_printer *p, unsigned int indent,
                              const struct drm_gem_object *obj)
{
        const struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
        drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
        drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
}
EXPORT_SYMBOL(drm_gem_shmem_print_info);

/**
 * drm_gem_shmem_get_sg_table - Provide a scatter/gather table of pinned
 *                              pages for a shmem GEM object
 * @obj: GEM object
 *
 * This function exports a scatter/gather table suitable for PRIME usage by
 * calling the standard DMA mapping API. Drivers should not call this function
 * directly, instead it should only be used as an implementation for
 * &drm_gem_object_funcs.get_sg_table.
 *
 * Drivers who need to acquire an scatter/gather table for objects need to call
 * drm_gem_shmem_get_pages_sgt() instead.
 *
 * Returns:
 * A pointer to the scatter/gather table of pinned pages or NULL on failure.
 */
struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_object *obj)
{
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);

        WARN_ON(shmem->base.import_attach);

        return drm_prime_pages_to_sg(obj->dev, shmem->pages, obj->size >> PAGE_SHIFT);
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_get_sg_table);

/**
 * drm_gem_shmem_get_pages_sgt - Pin pages, dma map them, and return a
 *                               scatter/gather table for a shmem GEM object.
 * @obj: GEM object
 *
 * This function returns a scatter/gather table suitable for driver usage. If
 * the sg table doesn't exist, the pages are pinned, dma-mapped, and a sg
 * table created.
 *
 * This is the main function for drivers to get at backing storage, and it hides
 * and difference between dma-buf imported and natively allocated objects.
 * drm_gem_shmem_get_sg_table() should not be directly called by drivers.
 *
 * Returns:
 * A pointer to the scatter/gather table of pinned pages or errno on failure.
 */
struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj)
{
        int ret;
        struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
        struct sg_table *sgt;

        if (shmem->sgt)
                return shmem->sgt;

        WARN_ON(obj->import_attach);

        ret = drm_gem_shmem_get_pages(shmem);
        if (ret)
                return ERR_PTR(ret);

        sgt = drm_gem_shmem_get_sg_table(&shmem->base);
        if (IS_ERR(sgt)) {
                ret = PTR_ERR(sgt);
                goto err_put_pages;
        }
        /* Map the pages for use by the h/w. */
        ret = dma_map_sgtable(obj->dev->dev, sgt, DMA_BIDIRECTIONAL, 0);
        if (ret)
                goto err_free_sgt;

        shmem->sgt = sgt;

        return sgt;

err_free_sgt:
        sg_free_table(sgt);
        kfree(sgt);
err_put_pages:
        drm_gem_shmem_put_pages(shmem);
        return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_get_pages_sgt);

/**
 * drm_gem_shmem_prime_import_sg_table - Produce a shmem GEM object from
 *                 another driver's scatter/gather table of pinned pages
 * @dev: Device to import into
 * @attach: DMA-BUF attachment
 * @sgt: Scatter/gather table of pinned pages
 *
 * This function imports a scatter/gather table exported via DMA-BUF by
 * another driver. Drivers that use the shmem helpers should set this as their
 * &drm_driver.gem_prime_import_sg_table callback.
 *
 * Returns:
 * A pointer to a newly created GEM object or an ERR_PTR-encoded negative
 * error code on failure.
 */
struct drm_gem_object *
drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
                                    struct dma_buf_attachment *attach,
                                    struct sg_table *sgt)
{
        size_t size = PAGE_ALIGN(attach->dmabuf->size);
        struct drm_gem_shmem_object *shmem;

        shmem = __drm_gem_shmem_create(dev, size, true);
        if (IS_ERR(shmem))
                return ERR_CAST(shmem);

        shmem->sgt = sgt;

        DRM_DEBUG_PRIME("size = %zu\n", size);

        return &shmem->base;
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);