Linux 4.19-rc7

[linux-2.6/btrfs-unstable.git] / drivers / dma-buf / dma-buf.c

/*
 * Framework for buffer objects that can be shared across devices/subsystems.
 *
 * Copyright(C) 2011 Linaro Limited. All rights reserved.
 * Author: Sumit Semwal <sumit.semwal@ti.com>
 *
 * Many thanks to linaro-mm-sig list, and specially
 * Arnd Bergmann <arnd@arndb.de>, Rob Clark <rob@ti.com> and
 * Daniel Vetter <daniel@ffwll.ch> for their support in creation and
 * refining of this idea.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/dma-buf.h>
#include <linux/dma-fence.h>
#include <linux/anon_inodes.h>
#include <linux/export.h>
#include <linux/debugfs.h>
#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
#include <linux/reservation.h>
#include <linux/mm.h>

#include <uapi/linux/dma-buf.h>

static inline int is_dma_buf_file(struct file *);

struct dma_buf_list {
        struct list_head head;
        struct mutex lock;
};

static struct dma_buf_list db_list;

static int dma_buf_release(struct inode *inode, struct file *file)
{
        struct dma_buf *dmabuf;

        if (!is_dma_buf_file(file))
                return -EINVAL;

        dmabuf = file->private_data;

        BUG_ON(dmabuf->vmapping_counter);

        /*
         * Any fences that a dma-buf poll can wait on should be signaled
         * before releasing dma-buf. This is the responsibility of each
         * driver that uses the reservation objects.
         *
         * If you hit this BUG() it means someone dropped their ref to the
         * dma-buf while still having pending operation to the buffer.
         */
        BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);

        dmabuf->ops->release(dmabuf);

        mutex_lock(&db_list.lock);
        list_del(&dmabuf->list_node);
        mutex_unlock(&db_list.lock);

        if (dmabuf->resv == (struct reservation_object *)&dmabuf[1])
                reservation_object_fini(dmabuf->resv);

        module_put(dmabuf->owner);
        kfree(dmabuf);
        return 0;
}

static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
{
        struct dma_buf *dmabuf;

        if (!is_dma_buf_file(file))
                return -EINVAL;

        dmabuf = file->private_data;

        /* check for overflowing the buffer's size */
        if (vma->vm_pgoff + vma_pages(vma) >
            dmabuf->size >> PAGE_SHIFT)
                return -EINVAL;

        return dmabuf->ops->mmap(dmabuf, vma);
}

static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
{
        struct dma_buf *dmabuf;
        loff_t base;

        if (!is_dma_buf_file(file))
                return -EBADF;

        dmabuf = file->private_data;

        /* only support discovering the end of the buffer,
           but also allow SEEK_SET to maintain the idiomatic
           SEEK_END(0), SEEK_CUR(0) pattern */
        if (whence == SEEK_END)
                base = dmabuf->size;
        else if (whence == SEEK_SET)
                base = 0;
        else
                return -EINVAL;

        if (offset != 0)
                return -EINVAL;

        return base + offset;
}

/**
 * DOC: fence polling
 *
 * To support cross-device and cross-driver synchronization of buffer access
 * implicit fences (represented internally in the kernel with &struct fence) can
 * be attached to a &dma_buf. The glue for that and a few related things are
 * provided in the &reservation_object structure.
 *
 * Userspace can query the state of these implicitly tracked fences using poll()
 * and related system calls:
 *
 * - Checking for EPOLLIN, i.e. read access, can be use to query the state of the
 *   most recent write or exclusive fence.
 *
 * - Checking for EPOLLOUT, i.e. write access, can be used to query the state of
 *   all attached fences, shared and exclusive ones.
 *
 * Note that this only signals the completion of the respective fences, i.e. the
 * DMA transfers are complete. Cache flushing and any other necessary
 * preparations before CPU access can begin still need to happen.
 */

static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
{
        struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb;
        unsigned long flags;

        spin_lock_irqsave(&dcb->poll->lock, flags);
        wake_up_locked_poll(dcb->poll, dcb->active);
        dcb->active = 0;
        spin_unlock_irqrestore(&dcb->poll->lock, flags);
}

static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
{
        struct dma_buf *dmabuf;
        struct reservation_object *resv;
        struct reservation_object_list *fobj;
        struct dma_fence *fence_excl;
        __poll_t events;
        unsigned shared_count, seq;

        dmabuf = file->private_data;
        if (!dmabuf || !dmabuf->resv)
                return EPOLLERR;

        resv = dmabuf->resv;

        poll_wait(file, &dmabuf->poll, poll);

        events = poll_requested_events(poll) & (EPOLLIN | EPOLLOUT);
        if (!events)
                return 0;

retry:
        seq = read_seqcount_begin(&resv->seq);
        rcu_read_lock();

        fobj = rcu_dereference(resv->fence);
        if (fobj)
                shared_count = fobj->shared_count;
        else
                shared_count = 0;
        fence_excl = rcu_dereference(resv->fence_excl);
        if (read_seqcount_retry(&resv->seq, seq)) {
                rcu_read_unlock();
                goto retry;
        }

        if (fence_excl && (!(events & EPOLLOUT) || shared_count == 0)) {
                struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl;
                __poll_t pevents = EPOLLIN;

                if (shared_count == 0)
                        pevents |= EPOLLOUT;

                spin_lock_irq(&dmabuf->poll.lock);
                if (dcb->active) {
                        dcb->active |= pevents;
                        events &= ~pevents;
                } else
                        dcb->active = pevents;
                spin_unlock_irq(&dmabuf->poll.lock);

                if (events & pevents) {
                        if (!dma_fence_get_rcu(fence_excl)) {
                                /* force a recheck */
                                events &= ~pevents;
                                dma_buf_poll_cb(NULL, &dcb->cb);
                        } else if (!dma_fence_add_callback(fence_excl, &dcb->cb,
                                                           dma_buf_poll_cb)) {
                                events &= ~pevents;
                                dma_fence_put(fence_excl);
                        } else {
                                /*
                                 * No callback queued, wake up any additional
                                 * waiters.
                                 */
                                dma_fence_put(fence_excl);
                                dma_buf_poll_cb(NULL, &dcb->cb);
                        }
                }
        }

        if ((events & EPOLLOUT) && shared_count > 0) {
                struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_shared;
                int i;

                /* Only queue a new callback if no event has fired yet */
                spin_lock_irq(&dmabuf->poll.lock);
                if (dcb->active)
                        events &= ~EPOLLOUT;
                else
                        dcb->active = EPOLLOUT;
                spin_unlock_irq(&dmabuf->poll.lock);

                if (!(events & EPOLLOUT))
                        goto out;

                for (i = 0; i < shared_count; ++i) {
                        struct dma_fence *fence = rcu_dereference(fobj->shared[i]);

                        if (!dma_fence_get_rcu(fence)) {
                                /*
                                 * fence refcount dropped to zero, this means
                                 * that fobj has been freed
                                 *
                                 * call dma_buf_poll_cb and force a recheck!
                                 */
                                events &= ~EPOLLOUT;
                                dma_buf_poll_cb(NULL, &dcb->cb);
                                break;
                        }
                        if (!dma_fence_add_callback(fence, &dcb->cb,
                                                    dma_buf_poll_cb)) {
                                dma_fence_put(fence);
                                events &= ~EPOLLOUT;
                                break;
                        }
                        dma_fence_put(fence);
                }

                /* No callback queued, wake up any additional waiters. */
                if (i == shared_count)
                        dma_buf_poll_cb(NULL, &dcb->cb);
        }

out:
        rcu_read_unlock();
        return events;
}

static long dma_buf_ioctl(struct file *file,
                          unsigned int cmd, unsigned long arg)
{
        struct dma_buf *dmabuf;
        struct dma_buf_sync sync;
        enum dma_data_direction direction;
        int ret;

        dmabuf = file->private_data;

        switch (cmd) {
        case DMA_BUF_IOCTL_SYNC:
                if (copy_from_user(&sync, (void __user *) arg, sizeof(sync)))
                        return -EFAULT;

                if (sync.flags & ~DMA_BUF_SYNC_VALID_FLAGS_MASK)
                        return -EINVAL;

                switch (sync.flags & DMA_BUF_SYNC_RW) {
                case DMA_BUF_SYNC_READ:
                        direction = DMA_FROM_DEVICE;
                        break;
                case DMA_BUF_SYNC_WRITE:
                        direction = DMA_TO_DEVICE;
                        break;
                case DMA_BUF_SYNC_RW:
                        direction = DMA_BIDIRECTIONAL;
                        break;
                default:
                        return -EINVAL;
                }

                if (sync.flags & DMA_BUF_SYNC_END)
                        ret = dma_buf_end_cpu_access(dmabuf, direction);
                else
                        ret = dma_buf_begin_cpu_access(dmabuf, direction);

                return ret;
        default:
                return -ENOTTY;
        }
}

static const struct file_operations dma_buf_fops = {
        .release        = dma_buf_release,
        .mmap           = dma_buf_mmap_internal,
        .llseek         = dma_buf_llseek,
        .poll           = dma_buf_poll,
        .unlocked_ioctl = dma_buf_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = dma_buf_ioctl,
#endif
};

/*
 * is_dma_buf_file - Check if struct file* is associated with dma_buf
 */
static inline int is_dma_buf_file(struct file *file)
{
        return file->f_op == &dma_buf_fops;
}

/**
 * DOC: dma buf device access
 *
 * For device DMA access to a shared DMA buffer the usual sequence of operations
 * is fairly simple:
 *
 * 1. The exporter defines his exporter instance using
 *    DEFINE_DMA_BUF_EXPORT_INFO() and calls dma_buf_export() to wrap a private
 *    buffer object into a &dma_buf. It then exports that &dma_buf to userspace
 *    as a file descriptor by calling dma_buf_fd().
 *
 * 2. Userspace passes this file-descriptors to all drivers it wants this buffer
 *    to share with: First the filedescriptor is converted to a &dma_buf using
 *    dma_buf_get(). Then the buffer is attached to the device using
 *    dma_buf_attach().
 *
 *    Up to this stage the exporter is still free to migrate or reallocate the
 *    backing storage.
 *
 * 3. Once the buffer is attached to all devices userspace can initiate DMA
 *    access to the shared buffer. In the kernel this is done by calling
 *    dma_buf_map_attachment() and dma_buf_unmap_attachment().
 *
 * 4. Once a driver is done with a shared buffer it needs to call
 *    dma_buf_detach() (after cleaning up any mappings) and then release the
 *    reference acquired with dma_buf_get by calling dma_buf_put().
 *
 * For the detailed semantics exporters are expected to implement see
 * &dma_buf_ops.
 */

/**
 * dma_buf_export - Creates a new dma_buf, and associates an anon file
 * with this buffer, so it can be exported.
 * Also connect the allocator specific data and ops to the buffer.
 * Additionally, provide a name string for exporter; useful in debugging.
 *
 * @exp_info:   [in]    holds all the export related information provided
 *                      by the exporter. see &struct dma_buf_export_info
 *                      for further details.
 *
 * Returns, on success, a newly created dma_buf object, which wraps the
 * supplied private data and operations for dma_buf_ops. On either missing
 * ops, or error in allocating struct dma_buf, will return negative error.
 *
 * For most cases the easiest way to create @exp_info is through the
 * %DEFINE_DMA_BUF_EXPORT_INFO macro.
 */
struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
{
        struct dma_buf *dmabuf;
        struct reservation_object *resv = exp_info->resv;
        struct file *file;
        size_t alloc_size = sizeof(struct dma_buf);
        int ret;

        if (!exp_info->resv)
                alloc_size += sizeof(struct reservation_object);
        else
                /* prevent &dma_buf[1] == dma_buf->resv */
                alloc_size += 1;

        if (WARN_ON(!exp_info->priv
                          || !exp_info->ops
                          || !exp_info->ops->map_dma_buf
                          || !exp_info->ops->unmap_dma_buf
                          || !exp_info->ops->release
                          || !exp_info->ops->map
                          || !exp_info->ops->mmap)) {
                return ERR_PTR(-EINVAL);
        }

        if (!try_module_get(exp_info->owner))
                return ERR_PTR(-ENOENT);

        dmabuf = kzalloc(alloc_size, GFP_KERNEL);
        if (!dmabuf) {
                ret = -ENOMEM;
                goto err_module;
        }

        dmabuf->priv = exp_info->priv;
        dmabuf->ops = exp_info->ops;
        dmabuf->size = exp_info->size;
        dmabuf->exp_name = exp_info->exp_name;
        dmabuf->owner = exp_info->owner;
        init_waitqueue_head(&dmabuf->poll);
        dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
        dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;

        if (!resv) {
                resv = (struct reservation_object *)&dmabuf[1];
                reservation_object_init(resv);
        }
        dmabuf->resv = resv;

        file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf,
                                        exp_info->flags);
        if (IS_ERR(file)) {
                ret = PTR_ERR(file);
                goto err_dmabuf;
        }

        file->f_mode |= FMODE_LSEEK;
        dmabuf->file = file;

        mutex_init(&dmabuf->lock);
        INIT_LIST_HEAD(&dmabuf->attachments);

        mutex_lock(&db_list.lock);
        list_add(&dmabuf->list_node, &db_list.head);
        mutex_unlock(&db_list.lock);

        return dmabuf;

err_dmabuf:
        kfree(dmabuf);
err_module:
        module_put(exp_info->owner);
        return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(dma_buf_export);

/**
 * dma_buf_fd - returns a file descriptor for the given dma_buf
 * @dmabuf:     [in]    pointer to dma_buf for which fd is required.
 * @flags:      [in]    flags to give to fd
 *
 * On success, returns an associated 'fd'. Else, returns error.
 */
int dma_buf_fd(struct dma_buf *dmabuf, int flags)
{
        int fd;

        if (!dmabuf || !dmabuf->file)
                return -EINVAL;

        fd = get_unused_fd_flags(flags);
        if (fd < 0)
                return fd;

        fd_install(fd, dmabuf->file);

        return fd;
}
EXPORT_SYMBOL_GPL(dma_buf_fd);

/**
 * dma_buf_get - returns the dma_buf structure related to an fd
 * @fd: [in]    fd associated with the dma_buf to be returned
 *
 * On success, returns the dma_buf structure associated with an fd; uses
 * file's refcounting done by fget to increase refcount. returns ERR_PTR
 * otherwise.
 */
struct dma_buf *dma_buf_get(int fd)
{
        struct file *file;

        file = fget(fd);

        if (!file)
                return ERR_PTR(-EBADF);

        if (!is_dma_buf_file(file)) {
                fput(file);
                return ERR_PTR(-EINVAL);
        }

        return file->private_data;
}
EXPORT_SYMBOL_GPL(dma_buf_get);

/**
 * dma_buf_put - decreases refcount of the buffer
 * @dmabuf:     [in]    buffer to reduce refcount of
 *
 * Uses file's refcounting done implicitly by fput().
 *
 * If, as a result of this call, the refcount becomes 0, the 'release' file
 * operation related to this fd is called. It calls &dma_buf_ops.release vfunc
 * in turn, and frees the memory allocated for dmabuf when exported.
 */
void dma_buf_put(struct dma_buf *dmabuf)
{
        if (WARN_ON(!dmabuf || !dmabuf->file))
                return;

        fput(dmabuf->file);
}
EXPORT_SYMBOL_GPL(dma_buf_put);

/**
 * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
 * calls attach() of dma_buf_ops to allow device-specific attach functionality
 * @dmabuf:     [in]    buffer to attach device to.
 * @dev:        [in]    device to be attached.
 *
 * Returns struct dma_buf_attachment pointer for this attachment. Attachments
 * must be cleaned up by calling dma_buf_detach().
 *
 * Returns:
 *
 * A pointer to newly created &dma_buf_attachment on success, or a negative
 * error code wrapped into a pointer on failure.
 *
 * Note that this can fail if the backing storage of @dmabuf is in a place not
 * accessible to @dev, and cannot be moved to a more suitable place. This is
 * indicated with the error code -EBUSY.
 */
struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
                                          struct device *dev)
{
        struct dma_buf_attachment *attach;
        int ret;

        if (WARN_ON(!dmabuf || !dev))
                return ERR_PTR(-EINVAL);

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

        attach->dev = dev;
        attach->dmabuf = dmabuf;

        mutex_lock(&dmabuf->lock);

        if (dmabuf->ops->attach) {
                ret = dmabuf->ops->attach(dmabuf, attach);
                if (ret)
                        goto err_attach;
        }
        list_add(&attach->node, &dmabuf->attachments);

        mutex_unlock(&dmabuf->lock);
        return attach;

err_attach:
        kfree(attach);
        mutex_unlock(&dmabuf->lock);
        return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(dma_buf_attach);

/**
 * dma_buf_detach - Remove the given attachment from dmabuf's attachments list;
 * optionally calls detach() of dma_buf_ops for device-specific detach
 * @dmabuf:     [in]    buffer to detach from.
 * @attach:     [in]    attachment to be detached; is free'd after this call.
 *
 * Clean up a device attachment obtained by calling dma_buf_attach().
 */
void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
{
        if (WARN_ON(!dmabuf || !attach))
                return;

        mutex_lock(&dmabuf->lock);
        list_del(&attach->node);
        if (dmabuf->ops->detach)
                dmabuf->ops->detach(dmabuf, attach);

        mutex_unlock(&dmabuf->lock);
        kfree(attach);
}
EXPORT_SYMBOL_GPL(dma_buf_detach);

/**
 * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
 * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
 * dma_buf_ops.
 * @attach:     [in]    attachment whose scatterlist is to be returned
 * @direction:  [in]    direction of DMA transfer
 *
 * Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
 * on error. May return -EINTR if it is interrupted by a signal.
 *
 * A mapping must be unmapped by using dma_buf_unmap_attachment(). Note that
 * the underlying backing storage is pinned for as long as a mapping exists,
 * therefore users/importers should not hold onto a mapping for undue amounts of
 * time.
 */
struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
                                        enum dma_data_direction direction)
{
        struct sg_table *sg_table;

        might_sleep();

        if (WARN_ON(!attach || !attach->dmabuf))
                return ERR_PTR(-EINVAL);

        sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
        if (!sg_table)
                sg_table = ERR_PTR(-ENOMEM);

        return sg_table;
}
EXPORT_SYMBOL_GPL(dma_buf_map_attachment);

/**
 * dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
 * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
 * dma_buf_ops.
 * @attach:     [in]    attachment to unmap buffer from
 * @sg_table:   [in]    scatterlist info of the buffer to unmap
 * @direction:  [in]    direction of DMA transfer
 *
 * This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment().
 */
void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
                                struct sg_table *sg_table,
                                enum dma_data_direction direction)
{
        might_sleep();

        if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
                return;

        attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
                                                direction);
}
EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);

/**
 * DOC: cpu access
 *
 * There are mutliple reasons for supporting CPU access to a dma buffer object:
 *
 * - Fallback operations in the kernel, for example when a device is connected
 *   over USB and the kernel needs to shuffle the data around first before
 *   sending it away. Cache coherency is handled by braketing any transactions
 *   with calls to dma_buf_begin_cpu_access() and dma_buf_end_cpu_access()
 *   access.
 *
 *   To support dma_buf objects residing in highmem cpu access is page-based
 *   using an api similar to kmap. Accessing a dma_buf is done in aligned chunks
 *   of PAGE_SIZE size. Before accessing a chunk it needs to be mapped, which
 *   returns a pointer in kernel virtual address space. Afterwards the chunk
 *   needs to be unmapped again. There is no limit on how often a given chunk
 *   can be mapped and unmapped, i.e. the importer does not need to call
 *   begin_cpu_access again before mapping the same chunk again.
 *
 *   Interfaces::
 *      void \*dma_buf_kmap(struct dma_buf \*, unsigned long);
 *      void dma_buf_kunmap(struct dma_buf \*, unsigned long, void \*);
 *
 *   Implementing the functions is optional for exporters and for importers all
 *   the restrictions of using kmap apply.
 *
 *   dma_buf kmap calls outside of the range specified in begin_cpu_access are
 *   undefined. If the range is not PAGE_SIZE aligned, kmap needs to succeed on
 *   the partial chunks at the beginning and end but may return stale or bogus
 *   data outside of the range (in these partial chunks).
 *
 *   For some cases the overhead of kmap can be too high, a vmap interface
 *   is introduced. This interface should be used very carefully, as vmalloc
 *   space is a limited resources on many architectures.
 *
 *   Interfaces::
 *      void \*dma_buf_vmap(struct dma_buf \*dmabuf)
 *      void dma_buf_vunmap(struct dma_buf \*dmabuf, void \*vaddr)
 *
 *   The vmap call can fail if there is no vmap support in the exporter, or if
 *   it runs out of vmalloc space. Fallback to kmap should be implemented. Note
 *   that the dma-buf layer keeps a reference count for all vmap access and
 *   calls down into the exporter's vmap function only when no vmapping exists,
 *   and only unmaps it once. Protection against concurrent vmap/vunmap calls is
 *   provided by taking the dma_buf->lock mutex.
 *
 * - For full compatibility on the importer side with existing userspace
 *   interfaces, which might already support mmap'ing buffers. This is needed in
 *   many processing pipelines (e.g. feeding a software rendered image into a
 *   hardware pipeline, thumbnail creation, snapshots, ...). Also, Android's ION
 *   framework already supported this and for DMA buffer file descriptors to
 *   replace ION buffers mmap support was needed.
 *
 *   There is no special interfaces, userspace simply calls mmap on the dma-buf
 *   fd. But like for CPU access there's a need to braket the actual access,
 *   which is handled by the ioctl (DMA_BUF_IOCTL_SYNC). Note that
 *   DMA_BUF_IOCTL_SYNC can fail with -EAGAIN or -EINTR, in which case it must
 *   be restarted.
 *
 *   Some systems might need some sort of cache coherency management e.g. when
 *   CPU and GPU domains are being accessed through dma-buf at the same time.
 *   To circumvent this problem there are begin/end coherency markers, that
 *   forward directly to existing dma-buf device drivers vfunc hooks. Userspace
 *   can make use of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The
 *   sequence would be used like following:
 *
 *     - mmap dma-buf fd
 *     - for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
 *       to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
 *       want (with the new data being consumed by say the GPU or the scanout
 *       device)
 *     - munmap once you don't need the buffer any more
 *
 *    For correctness and optimal performance, it is always required to use
 *    SYNC_START and SYNC_END before and after, respectively, when accessing the
 *    mapped address. Userspace cannot rely on coherent access, even when there
 *    are systems where it just works without calling these ioctls.
 *
 * - And as a CPU fallback in userspace processing pipelines.
 *
 *   Similar to the motivation for kernel cpu access it is again important that
 *   the userspace code of a given importing subsystem can use the same
 *   interfaces with a imported dma-buf buffer object as with a native buffer
 *   object. This is especially important for drm where the userspace part of
 *   contemporary OpenGL, X, and other drivers is huge, and reworking them to
 *   use a different way to mmap a buffer rather invasive.
 *
 *   The assumption in the current dma-buf interfaces is that redirecting the
 *   initial mmap is all that's needed. A survey of some of the existing
 *   subsystems shows that no driver seems to do any nefarious thing like
 *   syncing up with outstanding asynchronous processing on the device or
 *   allocating special resources at fault time. So hopefully this is good
 *   enough, since adding interfaces to intercept pagefaults and allow pte
 *   shootdowns would increase the complexity quite a bit.
 *
 *   Interface::
 *      int dma_buf_mmap(struct dma_buf \*, struct vm_area_struct \*,
 *                     unsigned long);
 *
 *   If the importing subsystem simply provides a special-purpose mmap call to
 *   set up a mapping in userspace, calling do_mmap with dma_buf->file will
 *   equally achieve that for a dma-buf object.
 */

static int __dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
                                      enum dma_data_direction direction)
{
        bool write = (direction == DMA_BIDIRECTIONAL ||
                      direction == DMA_TO_DEVICE);
        struct reservation_object *resv = dmabuf->resv;
        long ret;

        /* Wait on any implicit rendering fences */
        ret = reservation_object_wait_timeout_rcu(resv, write, true,
                                                  MAX_SCHEDULE_TIMEOUT);
        if (ret < 0)
                return ret;

        return 0;
}

/**
 * dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
 * cpu in the kernel context. Calls begin_cpu_access to allow exporter-specific
 * preparations. Coherency is only guaranteed in the specified range for the
 * specified access direction.
 * @dmabuf:     [in]    buffer to prepare cpu access for.
 * @direction:  [in]    length of range for cpu access.
 *
 * After the cpu access is complete the caller should call
 * dma_buf_end_cpu_access(). Only when cpu access is braketed by both calls is
 * it guaranteed to be coherent with other DMA access.
 *
 * Can return negative error values, returns 0 on success.
 */
int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
                             enum dma_data_direction direction)
{
        int ret = 0;

        if (WARN_ON(!dmabuf))
                return -EINVAL;

        if (dmabuf->ops->begin_cpu_access)
                ret = dmabuf->ops->begin_cpu_access(dmabuf, direction);

        /* Ensure that all fences are waited upon - but we first allow
         * the native handler the chance to do so more efficiently if it
         * chooses. A double invocation here will be reasonably cheap no-op.
         */
        if (ret == 0)
                ret = __dma_buf_begin_cpu_access(dmabuf, direction);

        return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);

/**
 * dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the
 * cpu in the kernel context. Calls end_cpu_access to allow exporter-specific
 * actions. Coherency is only guaranteed in the specified range for the
 * specified access direction.
 * @dmabuf:     [in]    buffer to complete cpu access for.
 * @direction:  [in]    length of range for cpu access.
 *
 * This terminates CPU access started with dma_buf_begin_cpu_access().
 *
 * Can return negative error values, returns 0 on success.
 */
int dma_buf_end_cpu_access(struct dma_buf *dmabuf,
                           enum dma_data_direction direction)
{
        int ret = 0;

        WARN_ON(!dmabuf);

        if (dmabuf->ops->end_cpu_access)
                ret = dmabuf->ops->end_cpu_access(dmabuf, direction);

        return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);

/**
 * dma_buf_kmap - Map a page of the buffer object into kernel address space. The
 * same restrictions as for kmap and friends apply.
 * @dmabuf:     [in]    buffer to map page from.
 * @page_num:   [in]    page in PAGE_SIZE units to map.
 *
 * This call must always succeed, any necessary preparations that might fail
 * need to be done in begin_cpu_access.
 */
void *dma_buf_kmap(struct dma_buf *dmabuf, unsigned long page_num)
{
        WARN_ON(!dmabuf);

        if (!dmabuf->ops->map)
                return NULL;
        return dmabuf->ops->map(dmabuf, page_num);
}
EXPORT_SYMBOL_GPL(dma_buf_kmap);

/**
 * dma_buf_kunmap - Unmap a page obtained by dma_buf_kmap.
 * @dmabuf:     [in]    buffer to unmap page from.
 * @page_num:   [in]    page in PAGE_SIZE units to unmap.
 * @vaddr:      [in]    kernel space pointer obtained from dma_buf_kmap.
 *
 * This call must always succeed.
 */
void dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long page_num,
                    void *vaddr)
{
        WARN_ON(!dmabuf);

        if (dmabuf->ops->unmap)
                dmabuf->ops->unmap(dmabuf, page_num, vaddr);
}
EXPORT_SYMBOL_GPL(dma_buf_kunmap);


/**
 * dma_buf_mmap - Setup up a userspace mmap with the given vma
 * @dmabuf:     [in]    buffer that should back the vma
 * @vma:        [in]    vma for the mmap
 * @pgoff:      [in]    offset in pages where this mmap should start within the
 *                      dma-buf buffer.
 *
 * This function adjusts the passed in vma so that it points at the file of the
 * dma_buf operation. It also adjusts the starting pgoff and does bounds
 * checking on the size of the vma. Then it calls the exporters mmap function to
 * set up the mapping.
 *
 * Can return negative error values, returns 0 on success.
 */
int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
                 unsigned long pgoff)
{
        struct file *oldfile;
        int ret;

        if (WARN_ON(!dmabuf || !vma))
                return -EINVAL;

        /* check for offset overflow */
        if (pgoff + vma_pages(vma) < pgoff)
                return -EOVERFLOW;

        /* check for overflowing the buffer's size */
        if (pgoff + vma_pages(vma) >
            dmabuf->size >> PAGE_SHIFT)
                return -EINVAL;

        /* readjust the vma */
        get_file(dmabuf->file);
        oldfile = vma->vm_file;
        vma->vm_file = dmabuf->file;
        vma->vm_pgoff = pgoff;

        ret = dmabuf->ops->mmap(dmabuf, vma);
        if (ret) {
                /* restore old parameters on failure */
                vma->vm_file = oldfile;
                fput(dmabuf->file);
        } else {
                if (oldfile)
                        fput(oldfile);
        }
        return ret;

}
EXPORT_SYMBOL_GPL(dma_buf_mmap);

/**
 * dma_buf_vmap - Create virtual mapping for the buffer object into kernel
 * address space. Same restrictions as for vmap and friends apply.
 * @dmabuf:     [in]    buffer to vmap
 *
 * This call may fail due to lack of virtual mapping address space.
 * These calls are optional in drivers. The intended use for them
 * is for mapping objects linear in kernel space for high use objects.
 * Please attempt to use kmap/kunmap before thinking about these interfaces.
 *
 * Returns NULL on error.
 */
void *dma_buf_vmap(struct dma_buf *dmabuf)
{
        void *ptr;

        if (WARN_ON(!dmabuf))
                return NULL;

        if (!dmabuf->ops->vmap)
                return NULL;

        mutex_lock(&dmabuf->lock);
        if (dmabuf->vmapping_counter) {
                dmabuf->vmapping_counter++;
                BUG_ON(!dmabuf->vmap_ptr);
                ptr = dmabuf->vmap_ptr;
                goto out_unlock;
        }

        BUG_ON(dmabuf->vmap_ptr);

        ptr = dmabuf->ops->vmap(dmabuf);
        if (WARN_ON_ONCE(IS_ERR(ptr)))
                ptr = NULL;
        if (!ptr)
                goto out_unlock;

        dmabuf->vmap_ptr = ptr;
        dmabuf->vmapping_counter = 1;

out_unlock:
        mutex_unlock(&dmabuf->lock);
        return ptr;
}
EXPORT_SYMBOL_GPL(dma_buf_vmap);

/**
 * dma_buf_vunmap - Unmap a vmap obtained by dma_buf_vmap.
 * @dmabuf:     [in]    buffer to vunmap
 * @vaddr:      [in]    vmap to vunmap
 */
void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
{
        if (WARN_ON(!dmabuf))
                return;

        BUG_ON(!dmabuf->vmap_ptr);
        BUG_ON(dmabuf->vmapping_counter == 0);
        BUG_ON(dmabuf->vmap_ptr != vaddr);

        mutex_lock(&dmabuf->lock);
        if (--dmabuf->vmapping_counter == 0) {
                if (dmabuf->ops->vunmap)
                        dmabuf->ops->vunmap(dmabuf, vaddr);
                dmabuf->vmap_ptr = NULL;
        }
        mutex_unlock(&dmabuf->lock);
}
EXPORT_SYMBOL_GPL(dma_buf_vunmap);

#ifdef CONFIG_DEBUG_FS
static int dma_buf_debug_show(struct seq_file *s, void *unused)
{
        int ret;
        struct dma_buf *buf_obj;
        struct dma_buf_attachment *attach_obj;
        struct reservation_object *robj;
        struct reservation_object_list *fobj;
        struct dma_fence *fence;
        unsigned seq;
        int count = 0, attach_count, shared_count, i;
        size_t size = 0;

        ret = mutex_lock_interruptible(&db_list.lock);

        if (ret)
                return ret;

        seq_puts(s, "\nDma-buf Objects:\n");
        seq_printf(s, "%-8s\t%-8s\t%-8s\t%-8s\texp_name\n",
                   "size", "flags", "mode", "count");

        list_for_each_entry(buf_obj, &db_list.head, list_node) {
                ret = mutex_lock_interruptible(&buf_obj->lock);

                if (ret) {
                        seq_puts(s,
                                 "\tERROR locking buffer object: skipping\n");
                        continue;
                }

                seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\n",
                                buf_obj->size,
                                buf_obj->file->f_flags, buf_obj->file->f_mode,
                                file_count(buf_obj->file),
                                buf_obj->exp_name);

                robj = buf_obj->resv;
                while (true) {
                        seq = read_seqcount_begin(&robj->seq);
                        rcu_read_lock();
                        fobj = rcu_dereference(robj->fence);
                        shared_count = fobj ? fobj->shared_count : 0;
                        fence = rcu_dereference(robj->fence_excl);
                        if (!read_seqcount_retry(&robj->seq, seq))
                                break;
                        rcu_read_unlock();
                }

                if (fence)
                        seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
                                   fence->ops->get_driver_name(fence),
                                   fence->ops->get_timeline_name(fence),
                                   dma_fence_is_signaled(fence) ? "" : "un");
                for (i = 0; i < shared_count; i++) {
                        fence = rcu_dereference(fobj->shared[i]);
                        if (!dma_fence_get_rcu(fence))
                                continue;
                        seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
                                   fence->ops->get_driver_name(fence),
                                   fence->ops->get_timeline_name(fence),
                                   dma_fence_is_signaled(fence) ? "" : "un");
                }
                rcu_read_unlock();

                seq_puts(s, "\tAttached Devices:\n");
                attach_count = 0;

                list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
                        seq_printf(s, "\t%s\n", dev_name(attach_obj->dev));
                        attach_count++;
                }

                seq_printf(s, "Total %d devices attached\n\n",
                                attach_count);

                count++;
                size += buf_obj->size;
                mutex_unlock(&buf_obj->lock);
        }

        seq_printf(s, "\nTotal %d objects, %zu bytes\n", count, size);

        mutex_unlock(&db_list.lock);
        return 0;
}

static int dma_buf_debug_open(struct inode *inode, struct file *file)
{
        return single_open(file, dma_buf_debug_show, NULL);
}

static const struct file_operations dma_buf_debug_fops = {
        .open           = dma_buf_debug_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

static struct dentry *dma_buf_debugfs_dir;

static int dma_buf_init_debugfs(void)
{
        struct dentry *d;
        int err = 0;

        d = debugfs_create_dir("dma_buf", NULL);
        if (IS_ERR(d))
                return PTR_ERR(d);

        dma_buf_debugfs_dir = d;

        d = debugfs_create_file("bufinfo", S_IRUGO, dma_buf_debugfs_dir,
                                NULL, &dma_buf_debug_fops);
        if (IS_ERR(d)) {
                pr_debug("dma_buf: debugfs: failed to create node bufinfo\n");
                debugfs_remove_recursive(dma_buf_debugfs_dir);
                dma_buf_debugfs_dir = NULL;
                err = PTR_ERR(d);
        }

        return err;
}

static void dma_buf_uninit_debugfs(void)
{
        debugfs_remove_recursive(dma_buf_debugfs_dir);
}
#else
static inline int dma_buf_init_debugfs(void)
{
        return 0;
}
static inline void dma_buf_uninit_debugfs(void)
{
}
#endif

static int __init dma_buf_init(void)
{
        mutex_init(&db_list.lock);
        INIT_LIST_HEAD(&db_list.head);
        dma_buf_init_debugfs();
        return 0;
}
subsys_initcall(dma_buf_init);

static void __exit dma_buf_deinit(void)
{
        dma_buf_uninit_debugfs();
}
__exitcall(dma_buf_deinit);