/*
 * Copyright © 2012 Red Hat
 *
 * 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 (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Authors:
 *      Dave Airlie <airlied@redhat.com>
 *      Rob Clark <rob.clark@linaro.org>
 *
 */

#include <linux/export.h>
#include <linux/dma-buf.h>
#include <drm/drmP.h>

/*
 * DMA-BUF/GEM Object references and lifetime overview:
 *
 * On the export the dma_buf holds a reference to the exporting GEM
 * object. It takes this reference in handle_to_fd_ioctl, when it
 * first calls .prime_export and stores the exporting GEM object in
 * the dma_buf priv. This reference is released when the dma_buf
 * object goes away in the driver .release function.
 *
 * On the import the importing GEM object holds a reference to the
 * dma_buf (which in turn holds a ref to the exporting GEM object).
 * It takes that reference in the fd_to_handle ioctl.
 * It calls dma_buf_get, creates an attachment to it and stores the
 * attachment in the GEM object. When this attachment is destroyed
 * when the imported object is destroyed, we remove the attachment
 * and drop the reference to the dma_buf.
 *
 * Thus the chain of references always flows in one direction
 * (avoiding loops): importing_gem -> dmabuf -> exporting_gem
 *
 * Self-importing: if userspace is using PRIME as a replacement for flink
 * then it will get a fd->handle request for a GEM object that it created.
 * Drivers should detect this situation and return back the gem object
 * from the dma-buf private.  Prime will do this automatically for drivers that
 * use the drm_gem_prime_{import,export} helpers.
 */

struct drm_prime_member {
        struct list_head entry;
        struct dma_buf *dma_buf;
        uint32_t handle;
};

struct drm_prime_attachment {
        struct sg_table *sgt;
        enum dma_data_direction dir;
};

static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
                                    struct dma_buf *dma_buf, uint32_t handle)
{
        struct drm_prime_member *member;

        member = kmalloc(sizeof(*member), GFP_KERNEL);
        if (!member)
                return -ENOMEM;

        get_dma_buf(dma_buf);
        member->dma_buf = dma_buf;
        member->handle = handle;
        list_add(&member->entry, &prime_fpriv->head);
        return 0;
}

static struct dma_buf *drm_prime_lookup_buf_by_handle(struct drm_prime_file_private *prime_fpriv,
                                                      uint32_t handle)
{
        struct drm_prime_member *member;

        list_for_each_entry(member, &prime_fpriv->head, entry) {
                if (member->handle == handle)
                        return member->dma_buf;
        }

        return NULL;
}

static int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv,
                                       struct dma_buf *dma_buf,
                                       uint32_t *handle)
{
        struct drm_prime_member *member;

        list_for_each_entry(member, &prime_fpriv->head, entry) {
                if (member->dma_buf == dma_buf) {
                        *handle = member->handle;
                        return 0;
                }
        }
        return -ENOENT;
}

static int drm_gem_map_attach(struct dma_buf *dma_buf,
                              struct device *target_dev,
                              struct dma_buf_attachment *attach)
{
        struct drm_prime_attachment *prime_attach;
        struct drm_gem_object *obj = dma_buf->priv;
        struct drm_device *dev = obj->dev;

        prime_attach = kzalloc(sizeof(*prime_attach), GFP_KERNEL);
        if (!prime_attach)
                return -ENOMEM;

        prime_attach->dir = DMA_NONE;
        attach->priv = prime_attach;

        if (!dev->driver->gem_prime_pin)
                return 0;

        return dev->driver->gem_prime_pin(obj);
}

static void drm_gem_map_detach(struct dma_buf *dma_buf,
                               struct dma_buf_attachment *attach)
{
        struct drm_prime_attachment *prime_attach = attach->priv;
        struct drm_gem_object *obj = dma_buf->priv;
        struct drm_device *dev = obj->dev;
        struct sg_table *sgt;

        if (dev->driver->gem_prime_unpin)
                dev->driver->gem_prime_unpin(obj);

        if (!prime_attach)
                return;

        sgt = prime_attach->sgt;
        if (sgt) {
                if (prime_attach->dir != DMA_NONE)
                        dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents,
                                        prime_attach->dir);
                sg_free_table(sgt);
        }

        kfree(sgt);
        kfree(prime_attach);
        attach->priv = NULL;
}

void drm_prime_remove_buf_handle_locked(struct drm_prime_file_private *prime_fpriv,
                                        struct dma_buf *dma_buf)
{
        struct drm_prime_member *member, *safe;

        list_for_each_entry_safe(member, safe, &prime_fpriv->head, entry) {
                if (member->dma_buf == dma_buf) {
                        dma_buf_put(dma_buf);
                        list_del(&member->entry);
                        kfree(member);
                }
        }
}

static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
                                            enum dma_data_direction dir)
{
        struct drm_prime_attachment *prime_attach = attach->priv;
        struct drm_gem_object *obj = attach->dmabuf->priv;
        struct sg_table *sgt;

        if (WARN_ON(dir == DMA_NONE || !prime_attach))
                return ERR_PTR(-EINVAL);

        /* return the cached mapping when possible */
        if (prime_attach->dir == dir)
                return prime_attach->sgt;

        /*
         * two mappings with different directions for the same attachment are
         * not allowed
         */
        if (WARN_ON(prime_attach->dir != DMA_NONE))
                return ERR_PTR(-EBUSY);

        sgt = obj->dev->driver->gem_prime_get_sg_table(obj);

        if (!IS_ERR(sgt)) {
                if (!dma_map_sg(attach->dev, sgt->sgl, sgt->nents, dir)) {
                        sg_free_table(sgt);
                        kfree(sgt);
                        sgt = ERR_PTR(-ENOMEM);
                } else {
                        prime_attach->sgt = sgt;
                        prime_attach->dir = dir;
                }
        }

        return sgt;
}

static void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
                                  struct sg_table *sgt,
                                  enum dma_data_direction dir)
{
        /* nothing to be done here */
}

/**
 * drm_gem_dmabuf_release - dma_buf release implementation for GEM
 * @dma_buf: buffer to be released
 *
 * Generic release function for dma_bufs exported as PRIME buffers. GEM drivers
 * must use this in their dma_buf ops structure as the release callback.
 */
void drm_gem_dmabuf_release(struct dma_buf *dma_buf)
{
        struct drm_gem_object *obj = dma_buf->priv;

        /* drop the reference on the export fd holds */
        drm_gem_object_unreference_unlocked(obj);
}
EXPORT_SYMBOL(drm_gem_dmabuf_release);

static void *drm_gem_dmabuf_vmap(struct dma_buf *dma_buf)
{
        struct drm_gem_object *obj = dma_buf->priv;
        struct drm_device *dev = obj->dev;

        return dev->driver->gem_prime_vmap(obj);
}

static void drm_gem_dmabuf_vunmap(struct dma_buf *dma_buf, void *vaddr)
{
        struct drm_gem_object *obj = dma_buf->priv;
        struct drm_device *dev = obj->dev;

        dev->driver->gem_prime_vunmap(obj, vaddr);
}

static void *drm_gem_dmabuf_kmap_atomic(struct dma_buf *dma_buf,
                                        unsigned long page_num)
{
        return NULL;
}

static void drm_gem_dmabuf_kunmap_atomic(struct dma_buf *dma_buf,
                                         unsigned long page_num, void *addr)
{

}
static void *drm_gem_dmabuf_kmap(struct dma_buf *dma_buf,
                                 unsigned long page_num)
{
        return NULL;
}

static void drm_gem_dmabuf_kunmap(struct dma_buf *dma_buf,
                                  unsigned long page_num, void *addr)
{

}

static int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf,
                               struct vm_area_struct *vma)
{
        struct drm_gem_object *obj = dma_buf->priv;
        struct drm_device *dev = obj->dev;

        if (!dev->driver->gem_prime_mmap)
                return -ENOSYS;

        return dev->driver->gem_prime_mmap(obj, vma);
}

static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
        .attach = drm_gem_map_attach,
        .detach = drm_gem_map_detach,
        .map_dma_buf = drm_gem_map_dma_buf,
        .unmap_dma_buf = drm_gem_unmap_dma_buf,
        .release = drm_gem_dmabuf_release,
        .kmap = drm_gem_dmabuf_kmap,
        .kmap_atomic = drm_gem_dmabuf_kmap_atomic,
        .kunmap = drm_gem_dmabuf_kunmap,
        .kunmap_atomic = drm_gem_dmabuf_kunmap_atomic,
        .mmap = drm_gem_dmabuf_mmap,
        .vmap = drm_gem_dmabuf_vmap,
        .vunmap = drm_gem_dmabuf_vunmap,
};

/**
 * DOC: PRIME Helpers
 *
 * Drivers can implement @gem_prime_export and @gem_prime_import in terms of
 * simpler APIs by using the helper functions @drm_gem_prime_export and
 * @drm_gem_prime_import.  These functions implement dma-buf support in terms of
 * five lower-level driver callbacks:
 *
 * Export callbacks:
 *
 *  - @gem_prime_pin (optional): prepare a GEM object for exporting
 *
 *  - @gem_prime_get_sg_table: provide a scatter/gather table of pinned pages
 *
 *  - @gem_prime_vmap: vmap a buffer exported by your driver
 *
 *  - @gem_prime_vunmap: vunmap a buffer exported by your driver
 *
 * Import callback:
 *
 *  - @gem_prime_import_sg_table (import): produce a GEM object from another
 *    driver's scatter/gather table
 */

/**
 * drm_gem_prime_export - helper library implemention of the export callback
 * @dev: drm_device to export from
 * @obj: GEM object to export
 * @flags: flags like DRM_CLOEXEC
 *
 * This is the implementation of the gem_prime_export functions for GEM drivers
 * using the PRIME helpers.
 */
struct dma_buf *drm_gem_prime_export(struct drm_device *dev,
                                     struct drm_gem_object *obj, int flags)
{
        return dma_buf_export(obj, &drm_gem_prime_dmabuf_ops, obj->size, flags);
}
EXPORT_SYMBOL(drm_gem_prime_export);

static struct dma_buf *export_and_register_object(struct drm_device *dev,
                                                  struct drm_gem_object *obj,
                                                  uint32_t flags)
{
        struct dma_buf *dmabuf;

        /* prevent races with concurrent gem_close. */
        if (obj->handle_count == 0) {
                dmabuf = ERR_PTR(-ENOENT);
                return dmabuf;
        }

        dmabuf = dev->driver->gem_prime_export(dev, obj, flags);
        if (IS_ERR(dmabuf)) {
                /* normally the created dma-buf takes ownership of the ref,
                 * but if that fails then drop the ref
                 */
                return dmabuf;
        }

        /*
         * Note that callers do not need to clean up the export cache
         * since the check for obj->handle_count guarantees that someone
         * will clean it up.
         */
        obj->dma_buf = dmabuf;
        get_dma_buf(obj->dma_buf);
        /* Grab a new ref since the callers is now used by the dma-buf */
        drm_gem_object_reference(obj);

        return dmabuf;
}

/**
 * drm_gem_prime_handle_to_fd - PRIME export function for GEM drivers
 * @dev: dev to export the buffer from
 * @file_priv: drm file-private structure
 * @handle: buffer handle to export
 * @flags: flags like DRM_CLOEXEC
 * @prime_fd: pointer to storage for the fd id of the create dma-buf
 *
 * This is the PRIME export function which must be used mandatorily by GEM
 * drivers to ensure correct lifetime management of the underlying GEM object.
 * The actual exporting from GEM object to a dma-buf is done through the
 * gem_prime_export driver callback.
 */
int drm_gem_prime_handle_to_fd(struct drm_device *dev,
                               struct drm_file *file_priv, uint32_t handle,
                               uint32_t flags,
                               int *prime_fd)
{
        struct drm_gem_object *obj;
        int ret = 0;
        struct dma_buf *dmabuf;

        mutex_lock(&file_priv->prime.lock);
        obj = drm_gem_object_lookup(dev, file_priv, handle);
        if (!obj)  {
                ret = -ENOENT;
                goto out_unlock;
        }

        dmabuf = drm_prime_lookup_buf_by_handle(&file_priv->prime, handle);
        if (dmabuf) {
                get_dma_buf(dmabuf);
                goto out_have_handle;
        }

        mutex_lock(&dev->object_name_lock);
        /* re-export the original imported object */
        if (obj->import_attach) {
                dmabuf = obj->import_attach->dmabuf;
                get_dma_buf(dmabuf);
                goto out_have_obj;
        }

        if (obj->dma_buf) {
                get_dma_buf(obj->dma_buf);
                dmabuf = obj->dma_buf;
                goto out_have_obj;
        }

        dmabuf = export_and_register_object(dev, obj, flags);
        if (IS_ERR(dmabuf)) {
                /* normally the created dma-buf takes ownership of the ref,
                 * but if that fails then drop the ref
                 */
                ret = PTR_ERR(dmabuf);
                mutex_unlock(&dev->object_name_lock);
                goto out;
        }

out_have_obj:
        /*
         * If we've exported this buffer then cheat and add it to the import list
         * so we get the correct handle back. We must do this under the
         * protection of dev->object_name_lock to ensure that a racing gem close
         * ioctl doesn't miss to remove this buffer handle from the cache.
         */
        ret = drm_prime_add_buf_handle(&file_priv->prime,
                                       dmabuf, handle);
        mutex_unlock(&dev->object_name_lock);
        if (ret)
                goto fail_put_dmabuf;

out_have_handle:
        ret = dma_buf_fd(dmabuf, flags);
        /*
         * We must _not_ remove the buffer from the handle cache since the newly
         * created dma buf is already linked in the global obj->dma_buf pointer,
         * and that is invariant as long as a userspace gem handle exists.
         * Closing the handle will clean out the cache anyway, so we don't leak.
         */
        if (ret < 0) {
                goto fail_put_dmabuf;
        } else {
                *prime_fd = ret;
                ret = 0;
        }

        goto out;

fail_put_dmabuf:
        dma_buf_put(dmabuf);
out:
        drm_gem_object_unreference_unlocked(obj);
out_unlock:
        mutex_unlock(&file_priv->prime.lock);

        return ret;
}
EXPORT_SYMBOL(drm_gem_prime_handle_to_fd);

/**
 * drm_gem_prime_import - helper library implemention of the import callback
 * @dev: drm_device to import into
 * @dma_buf: dma-buf object to import
 *
 * This is the implementation of the gem_prime_import functions for GEM drivers
 * using the PRIME helpers.
 */
struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
                                            struct dma_buf *dma_buf)
{
        struct dma_buf_attachment *attach;
        struct sg_table *sgt;
        struct drm_gem_object *obj;
        int ret;

        if (!dev->driver->gem_prime_import_sg_table)
                return ERR_PTR(-EINVAL);

        if (dma_buf->ops == &drm_gem_prime_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_reference(obj);
                        return obj;
                }
        }

        attach = dma_buf_attach(dma_buf, dev->dev);
        if (IS_ERR(attach))
                return ERR_CAST(attach);

        get_dma_buf(dma_buf);

        sgt = dma_buf_map_attachment(attach, DMA_BIDIRECTIONAL);
        if (IS_ERR(sgt)) {
                ret = PTR_ERR(sgt);
                goto fail_detach;
        }

        obj = dev->driver->gem_prime_import_sg_table(dev, dma_buf->size, sgt);
        if (IS_ERR(obj)) {
                ret = PTR_ERR(obj);
                goto fail_unmap;
        }

        obj->import_attach = attach;

        return obj;

fail_unmap:
        dma_buf_unmap_attachment(attach, sgt, DMA_BIDIRECTIONAL);
fail_detach:
        dma_buf_detach(dma_buf, attach);
        dma_buf_put(dma_buf);

        return ERR_PTR(ret);
}
EXPORT_SYMBOL(drm_gem_prime_import);

/**
 * drm_gem_prime_fd_to_handle - PRIME import function for GEM drivers
 * @dev: dev to export the buffer from
 * @file_priv: drm file-private structure
 * @prime_fd: fd id of the dma-buf which should be imported
 * @handle: pointer to storage for the handle of the imported buffer object
 *
 * This is the PRIME import function which must be used mandatorily by GEM
 * drivers to ensure correct lifetime management of the underlying GEM object.
 * The actual importing of GEM object from the dma-buf is done through the
 * gem_import_export driver callback.
 */
int drm_gem_prime_fd_to_handle(struct drm_device *dev,
                               struct drm_file *file_priv, int prime_fd,
                               uint32_t *handle)
{
        struct dma_buf *dma_buf;
        struct drm_gem_object *obj;
        int ret;

        dma_buf = dma_buf_get(prime_fd);
        if (IS_ERR(dma_buf))
                return PTR_ERR(dma_buf);

        mutex_lock(&file_priv->prime.lock);

        ret = drm_prime_lookup_buf_handle(&file_priv->prime,
                        dma_buf, handle);
        if (ret == 0)
                goto out_put;

        /* never seen this one, need to import */
        mutex_lock(&dev->object_name_lock);
        obj = dev->driver->gem_prime_import(dev, dma_buf);
        if (IS_ERR(obj)) {
                ret = PTR_ERR(obj);
                goto out_unlock;
        }

        if (obj->dma_buf) {
                WARN_ON(obj->dma_buf != dma_buf);
        } else {
                obj->dma_buf = dma_buf;
                get_dma_buf(dma_buf);
        }

        /* drm_gem_handle_create_tail unlocks dev->object_name_lock. */
        ret = drm_gem_handle_create_tail(file_priv, obj, handle);
        drm_gem_object_unreference_unlocked(obj);
        if (ret)
                goto out_put;

        ret = drm_prime_add_buf_handle(&file_priv->prime,
                        dma_buf, *handle);
        if (ret)
                goto fail;

        mutex_unlock(&file_priv->prime.lock);

        dma_buf_put(dma_buf);

        return 0;

fail:
        /* hmm, if driver attached, we are relying on the free-object path
         * to detach.. which seems ok..
         */
        drm_gem_handle_delete(file_priv, *handle);
out_unlock:
        mutex_unlock(&dev->object_name_lock);
out_put:
        dma_buf_put(dma_buf);
        mutex_unlock(&file_priv->prime.lock);
        return ret;
}
EXPORT_SYMBOL(drm_gem_prime_fd_to_handle);

int drm_prime_handle_to_fd_ioctl(struct drm_device *dev, void *data,
                                 struct drm_file *file_priv)
{
        struct drm_prime_handle *args = data;
        uint32_t flags;

        if (!drm_core_check_feature(dev, DRIVER_PRIME))
                return -EINVAL;

        if (!dev->driver->prime_handle_to_fd)
                return -ENOSYS;

        /* check flags are valid */
        if (args->flags & ~DRM_CLOEXEC)
                return -EINVAL;

        /* we only want to pass DRM_CLOEXEC which is == O_CLOEXEC */
        flags = args->flags & DRM_CLOEXEC;

        return dev->driver->prime_handle_to_fd(dev, file_priv,
                        args->handle, flags, &args->fd);
}

int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
                                 struct drm_file *file_priv)
{
        struct drm_prime_handle *args = data;

        if (!drm_core_check_feature(dev, DRIVER_PRIME))
                return -EINVAL;

        if (!dev->driver->prime_fd_to_handle)
                return -ENOSYS;

        return dev->driver->prime_fd_to_handle(dev, file_priv,
                        args->fd, &args->handle);
}

/**
 * drm_prime_pages_to_sg - converts a page array into an sg list
 * @pages: pointer to the array of page pointers to convert
 * @nr_pages: length of the page vector
 *
 * This helper creates an sg table object from a set of pages
 * the driver is responsible for mapping the pages into the
 * importers address space for use with dma_buf itself.
 */
struct sg_table *drm_prime_pages_to_sg(struct page **pages, int nr_pages)
{
        struct sg_table *sg = NULL;
        int ret;

        sg = kmalloc(sizeof(struct sg_table), GFP_KERNEL);
        if (!sg) {
                ret = -ENOMEM;
                goto out;
        }

        ret = sg_alloc_table_from_pages(sg, pages, nr_pages, 0,
                                nr_pages << PAGE_SHIFT, GFP_KERNEL);
        if (ret)
                goto out;

        return sg;
out:
        kfree(sg);
        return ERR_PTR(ret);
}
EXPORT_SYMBOL(drm_prime_pages_to_sg);

/**
 * drm_prime_sg_to_page_addr_arrays - convert an sg table into a page array
 * @sgt: scatter-gather table to convert
 * @pages: array of page pointers to store the page array in
 * @addrs: optional array to store the dma bus address of each page
 * @max_pages: size of both the passed-in arrays
 *
 * Exports an sg table into an array of pages and addresses. This is currently
 * required by the TTM driver in order to do correct fault handling.
 */
int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
                                     dma_addr_t *addrs, int max_pages)
{
        unsigned count;
        struct scatterlist *sg;
        struct page *page;
        u32 len;
        int pg_index;
        dma_addr_t addr;

        pg_index = 0;
        for_each_sg(sgt->sgl, sg, sgt->nents, count) {
                len = sg->length;
                page = sg_page(sg);
                addr = sg_dma_address(sg);

                while (len > 0) {
                        if (WARN_ON(pg_index >= max_pages))
                                return -1;
                        pages[pg_index] = page;
                        if (addrs)
                                addrs[pg_index] = addr;

                        page++;
                        addr += PAGE_SIZE;
                        len -= PAGE_SIZE;
                        pg_index++;
                }
        }
        return 0;
}
EXPORT_SYMBOL(drm_prime_sg_to_page_addr_arrays);

/**
 * drm_prime_gem_destroy - helper to clean up a PRIME-imported GEM object
 * @obj: GEM object which was created from a dma-buf
 * @sg: the sg-table which was pinned at import time
 *
 * This is the cleanup functions which GEM drivers need to call when they use
 * @drm_gem_prime_import to import dma-bufs.
 */
void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg)
{
        struct dma_buf_attachment *attach;
        struct dma_buf *dma_buf;
        attach = obj->import_attach;
        if (sg)
                dma_buf_unmap_attachment(attach, sg, DMA_BIDIRECTIONAL);
        dma_buf = attach->dmabuf;
        dma_buf_detach(attach->dmabuf, attach);
        /* remove the reference */
        dma_buf_put(dma_buf);
}
EXPORT_SYMBOL(drm_prime_gem_destroy);

void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv)
{
        INIT_LIST_HEAD(&prime_fpriv->head);
        mutex_init(&prime_fpriv->lock);
}

void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv)
{
        /* by now drm_gem_release should've made sure the list is empty */
        WARN_ON(!list_empty(&prime_fpriv->head));
}