1 // SPDX-License-Identifier: GPL-2.0-only
3 * Framework for buffer objects that can be shared across devices/subsystems.
5 * Copyright(C) 2011 Linaro Limited. All rights reserved.
6 * Author: Sumit Semwal <sumit.semwal@ti.com>
8 * Many thanks to linaro-mm-sig list, and specially
9 * Arnd Bergmann <arnd@arndb.de>, Rob Clark <rob@ti.com> and
10 * Daniel Vetter <daniel@ffwll.ch> for their support in creation and
11 * refining of this idea.
15 #include <linux/slab.h>
16 #include <linux/dma-buf.h>
17 #include <linux/dma-fence.h>
18 #include <linux/anon_inodes.h>
19 #include <linux/export.h>
20 #include <linux/debugfs.h>
21 #include <linux/module.h>
22 #include <linux/seq_file.h>
23 #include <linux/poll.h>
24 #include <linux/dma-resv.h>
26 #include <linux/mount.h>
27 #include <linux/pseudo_fs.h>
29 #include <uapi/linux/dma-buf.h>
30 #include <uapi/linux/magic.h>
32 static inline int is_dma_buf_file(struct file *);
35 struct list_head head;
39 static struct dma_buf_list db_list;
41 static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
43 struct dma_buf *dmabuf;
44 char name[DMA_BUF_NAME_LEN];
47 dmabuf = dentry->d_fsdata;
48 dma_resv_lock(dmabuf->resv, NULL);
50 ret = strlcpy(name, dmabuf->name, DMA_BUF_NAME_LEN);
51 dma_resv_unlock(dmabuf->resv);
53 return dynamic_dname(dentry, buffer, buflen, "/%s:%s",
54 dentry->d_name.name, ret > 0 ? name : "");
57 static const struct dentry_operations dma_buf_dentry_ops = {
58 .d_dname = dmabuffs_dname,
61 static struct vfsmount *dma_buf_mnt;
63 static int dma_buf_fs_init_context(struct fs_context *fc)
65 struct pseudo_fs_context *ctx;
67 ctx = init_pseudo(fc, DMA_BUF_MAGIC);
70 ctx->dops = &dma_buf_dentry_ops;
74 static struct file_system_type dma_buf_fs_type = {
76 .init_fs_context = dma_buf_fs_init_context,
77 .kill_sb = kill_anon_super,
80 static int dma_buf_release(struct inode *inode, struct file *file)
82 struct dma_buf *dmabuf;
84 if (!is_dma_buf_file(file))
87 dmabuf = file->private_data;
89 BUG_ON(dmabuf->vmapping_counter);
92 * Any fences that a dma-buf poll can wait on should be signaled
93 * before releasing dma-buf. This is the responsibility of each
94 * driver that uses the reservation objects.
96 * If you hit this BUG() it means someone dropped their ref to the
97 * dma-buf while still having pending operation to the buffer.
99 BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);
101 dmabuf->ops->release(dmabuf);
103 mutex_lock(&db_list.lock);
104 list_del(&dmabuf->list_node);
105 mutex_unlock(&db_list.lock);
107 if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
108 dma_resv_fini(dmabuf->resv);
110 module_put(dmabuf->owner);
116 static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
118 struct dma_buf *dmabuf;
120 if (!is_dma_buf_file(file))
123 dmabuf = file->private_data;
125 /* check if buffer supports mmap */
126 if (!dmabuf->ops->mmap)
129 /* check for overflowing the buffer's size */
130 if (vma->vm_pgoff + vma_pages(vma) >
131 dmabuf->size >> PAGE_SHIFT)
134 return dmabuf->ops->mmap(dmabuf, vma);
137 static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
139 struct dma_buf *dmabuf;
142 if (!is_dma_buf_file(file))
145 dmabuf = file->private_data;
147 /* only support discovering the end of the buffer,
148 but also allow SEEK_SET to maintain the idiomatic
149 SEEK_END(0), SEEK_CUR(0) pattern */
150 if (whence == SEEK_END)
152 else if (whence == SEEK_SET)
160 return base + offset;
166 * To support cross-device and cross-driver synchronization of buffer access
167 * implicit fences (represented internally in the kernel with &struct fence) can
168 * be attached to a &dma_buf. The glue for that and a few related things are
169 * provided in the &dma_resv structure.
171 * Userspace can query the state of these implicitly tracked fences using poll()
172 * and related system calls:
174 * - Checking for EPOLLIN, i.e. read access, can be use to query the state of the
175 * most recent write or exclusive fence.
177 * - Checking for EPOLLOUT, i.e. write access, can be used to query the state of
178 * all attached fences, shared and exclusive ones.
180 * Note that this only signals the completion of the respective fences, i.e. the
181 * DMA transfers are complete. Cache flushing and any other necessary
182 * preparations before CPU access can begin still need to happen.
185 static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
187 struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb;
190 spin_lock_irqsave(&dcb->poll->lock, flags);
191 wake_up_locked_poll(dcb->poll, dcb->active);
193 spin_unlock_irqrestore(&dcb->poll->lock, flags);
196 static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
198 struct dma_buf *dmabuf;
199 struct dma_resv *resv;
200 struct dma_resv_list *fobj;
201 struct dma_fence *fence_excl;
203 unsigned shared_count, seq;
205 dmabuf = file->private_data;
206 if (!dmabuf || !dmabuf->resv)
211 poll_wait(file, &dmabuf->poll, poll);
213 events = poll_requested_events(poll) & (EPOLLIN | EPOLLOUT);
218 seq = read_seqcount_begin(&resv->seq);
221 fobj = rcu_dereference(resv->fence);
223 shared_count = fobj->shared_count;
226 fence_excl = rcu_dereference(resv->fence_excl);
227 if (read_seqcount_retry(&resv->seq, seq)) {
232 if (fence_excl && (!(events & EPOLLOUT) || shared_count == 0)) {
233 struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl;
234 __poll_t pevents = EPOLLIN;
236 if (shared_count == 0)
239 spin_lock_irq(&dmabuf->poll.lock);
241 dcb->active |= pevents;
244 dcb->active = pevents;
245 spin_unlock_irq(&dmabuf->poll.lock);
247 if (events & pevents) {
248 if (!dma_fence_get_rcu(fence_excl)) {
249 /* force a recheck */
251 dma_buf_poll_cb(NULL, &dcb->cb);
252 } else if (!dma_fence_add_callback(fence_excl, &dcb->cb,
255 dma_fence_put(fence_excl);
258 * No callback queued, wake up any additional
261 dma_fence_put(fence_excl);
262 dma_buf_poll_cb(NULL, &dcb->cb);
267 if ((events & EPOLLOUT) && shared_count > 0) {
268 struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_shared;
271 /* Only queue a new callback if no event has fired yet */
272 spin_lock_irq(&dmabuf->poll.lock);
276 dcb->active = EPOLLOUT;
277 spin_unlock_irq(&dmabuf->poll.lock);
279 if (!(events & EPOLLOUT))
282 for (i = 0; i < shared_count; ++i) {
283 struct dma_fence *fence = rcu_dereference(fobj->shared[i]);
285 if (!dma_fence_get_rcu(fence)) {
287 * fence refcount dropped to zero, this means
288 * that fobj has been freed
290 * call dma_buf_poll_cb and force a recheck!
293 dma_buf_poll_cb(NULL, &dcb->cb);
296 if (!dma_fence_add_callback(fence, &dcb->cb,
298 dma_fence_put(fence);
302 dma_fence_put(fence);
305 /* No callback queued, wake up any additional waiters. */
306 if (i == shared_count)
307 dma_buf_poll_cb(NULL, &dcb->cb);
316 * dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
317 * The name of the dma-buf buffer can only be set when the dma-buf is not
318 * attached to any devices. It could theoritically support changing the
319 * name of the dma-buf if the same piece of memory is used for multiple
320 * purpose between different devices.
322 * @dmabuf [in] dmabuf buffer that will be renamed.
323 * @buf: [in] A piece of userspace memory that contains the name of
326 * Returns 0 on success. If the dma-buf buffer is already attached to
327 * devices, return -EBUSY.
330 static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
332 char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
336 return PTR_ERR(name);
338 dma_resv_lock(dmabuf->resv, NULL);
339 if (!list_empty(&dmabuf->attachments)) {
348 dma_resv_unlock(dmabuf->resv);
352 static long dma_buf_ioctl(struct file *file,
353 unsigned int cmd, unsigned long arg)
355 struct dma_buf *dmabuf;
356 struct dma_buf_sync sync;
357 enum dma_data_direction direction;
360 dmabuf = file->private_data;
363 case DMA_BUF_IOCTL_SYNC:
364 if (copy_from_user(&sync, (void __user *) arg, sizeof(sync)))
367 if (sync.flags & ~DMA_BUF_SYNC_VALID_FLAGS_MASK)
370 switch (sync.flags & DMA_BUF_SYNC_RW) {
371 case DMA_BUF_SYNC_READ:
372 direction = DMA_FROM_DEVICE;
374 case DMA_BUF_SYNC_WRITE:
375 direction = DMA_TO_DEVICE;
377 case DMA_BUF_SYNC_RW:
378 direction = DMA_BIDIRECTIONAL;
384 if (sync.flags & DMA_BUF_SYNC_END)
385 ret = dma_buf_end_cpu_access(dmabuf, direction);
387 ret = dma_buf_begin_cpu_access(dmabuf, direction);
391 case DMA_BUF_SET_NAME:
392 return dma_buf_set_name(dmabuf, (const char __user *)arg);
399 static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
401 struct dma_buf *dmabuf = file->private_data;
403 seq_printf(m, "size:\t%zu\n", dmabuf->size);
404 /* Don't count the temporary reference taken inside procfs seq_show */
405 seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1);
406 seq_printf(m, "exp_name:\t%s\n", dmabuf->exp_name);
407 dma_resv_lock(dmabuf->resv, NULL);
409 seq_printf(m, "name:\t%s\n", dmabuf->name);
410 dma_resv_unlock(dmabuf->resv);
413 static const struct file_operations dma_buf_fops = {
414 .release = dma_buf_release,
415 .mmap = dma_buf_mmap_internal,
416 .llseek = dma_buf_llseek,
417 .poll = dma_buf_poll,
418 .unlocked_ioctl = dma_buf_ioctl,
419 .compat_ioctl = compat_ptr_ioctl,
420 .show_fdinfo = dma_buf_show_fdinfo,
424 * is_dma_buf_file - Check if struct file* is associated with dma_buf
426 static inline int is_dma_buf_file(struct file *file)
428 return file->f_op == &dma_buf_fops;
431 static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
434 struct inode *inode = alloc_anon_inode(dma_buf_mnt->mnt_sb);
437 return ERR_CAST(inode);
439 inode->i_size = dmabuf->size;
440 inode_set_bytes(inode, dmabuf->size);
442 file = alloc_file_pseudo(inode, dma_buf_mnt, "dmabuf",
443 flags, &dma_buf_fops);
446 file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
447 file->private_data = dmabuf;
448 file->f_path.dentry->d_fsdata = dmabuf;
458 * DOC: dma buf device access
460 * For device DMA access to a shared DMA buffer the usual sequence of operations
463 * 1. The exporter defines his exporter instance using
464 * DEFINE_DMA_BUF_EXPORT_INFO() and calls dma_buf_export() to wrap a private
465 * buffer object into a &dma_buf. It then exports that &dma_buf to userspace
466 * as a file descriptor by calling dma_buf_fd().
468 * 2. Userspace passes this file-descriptors to all drivers it wants this buffer
469 * to share with: First the filedescriptor is converted to a &dma_buf using
470 * dma_buf_get(). Then the buffer is attached to the device using
473 * Up to this stage the exporter is still free to migrate or reallocate the
476 * 3. Once the buffer is attached to all devices userspace can initiate DMA
477 * access to the shared buffer. In the kernel this is done by calling
478 * dma_buf_map_attachment() and dma_buf_unmap_attachment().
480 * 4. Once a driver is done with a shared buffer it needs to call
481 * dma_buf_detach() (after cleaning up any mappings) and then release the
482 * reference acquired with dma_buf_get by calling dma_buf_put().
484 * For the detailed semantics exporters are expected to implement see
489 * dma_buf_export - Creates a new dma_buf, and associates an anon file
490 * with this buffer, so it can be exported.
491 * Also connect the allocator specific data and ops to the buffer.
492 * Additionally, provide a name string for exporter; useful in debugging.
494 * @exp_info: [in] holds all the export related information provided
495 * by the exporter. see &struct dma_buf_export_info
496 * for further details.
498 * Returns, on success, a newly created dma_buf object, which wraps the
499 * supplied private data and operations for dma_buf_ops. On either missing
500 * ops, or error in allocating struct dma_buf, will return negative error.
502 * For most cases the easiest way to create @exp_info is through the
503 * %DEFINE_DMA_BUF_EXPORT_INFO macro.
505 struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
507 struct dma_buf *dmabuf;
508 struct dma_resv *resv = exp_info->resv;
510 size_t alloc_size = sizeof(struct dma_buf);
514 alloc_size += sizeof(struct dma_resv);
516 /* prevent &dma_buf[1] == dma_buf->resv */
519 if (WARN_ON(!exp_info->priv
521 || !exp_info->ops->map_dma_buf
522 || !exp_info->ops->unmap_dma_buf
523 || !exp_info->ops->release)) {
524 return ERR_PTR(-EINVAL);
527 if (WARN_ON(exp_info->ops->cache_sgt_mapping &&
528 exp_info->ops->dynamic_mapping))
529 return ERR_PTR(-EINVAL);
531 if (!try_module_get(exp_info->owner))
532 return ERR_PTR(-ENOENT);
534 dmabuf = kzalloc(alloc_size, GFP_KERNEL);
540 dmabuf->priv = exp_info->priv;
541 dmabuf->ops = exp_info->ops;
542 dmabuf->size = exp_info->size;
543 dmabuf->exp_name = exp_info->exp_name;
544 dmabuf->owner = exp_info->owner;
545 init_waitqueue_head(&dmabuf->poll);
546 dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
547 dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;
550 resv = (struct dma_resv *)&dmabuf[1];
555 file = dma_buf_getfile(dmabuf, exp_info->flags);
561 file->f_mode |= FMODE_LSEEK;
564 mutex_init(&dmabuf->lock);
565 INIT_LIST_HEAD(&dmabuf->attachments);
567 mutex_lock(&db_list.lock);
568 list_add(&dmabuf->list_node, &db_list.head);
569 mutex_unlock(&db_list.lock);
576 module_put(exp_info->owner);
579 EXPORT_SYMBOL_GPL(dma_buf_export);
582 * dma_buf_fd - returns a file descriptor for the given dma_buf
583 * @dmabuf: [in] pointer to dma_buf for which fd is required.
584 * @flags: [in] flags to give to fd
586 * On success, returns an associated 'fd'. Else, returns error.
588 int dma_buf_fd(struct dma_buf *dmabuf, int flags)
592 if (!dmabuf || !dmabuf->file)
595 fd = get_unused_fd_flags(flags);
599 fd_install(fd, dmabuf->file);
603 EXPORT_SYMBOL_GPL(dma_buf_fd);
606 * dma_buf_get - returns the dma_buf structure related to an fd
607 * @fd: [in] fd associated with the dma_buf to be returned
609 * On success, returns the dma_buf structure associated with an fd; uses
610 * file's refcounting done by fget to increase refcount. returns ERR_PTR
613 struct dma_buf *dma_buf_get(int fd)
620 return ERR_PTR(-EBADF);
622 if (!is_dma_buf_file(file)) {
624 return ERR_PTR(-EINVAL);
627 return file->private_data;
629 EXPORT_SYMBOL_GPL(dma_buf_get);
632 * dma_buf_put - decreases refcount of the buffer
633 * @dmabuf: [in] buffer to reduce refcount of
635 * Uses file's refcounting done implicitly by fput().
637 * If, as a result of this call, the refcount becomes 0, the 'release' file
638 * operation related to this fd is called. It calls &dma_buf_ops.release vfunc
639 * in turn, and frees the memory allocated for dmabuf when exported.
641 void dma_buf_put(struct dma_buf *dmabuf)
643 if (WARN_ON(!dmabuf || !dmabuf->file))
648 EXPORT_SYMBOL_GPL(dma_buf_put);
651 * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list; optionally,
652 * calls attach() of dma_buf_ops to allow device-specific attach functionality
653 * @dmabuf: [in] buffer to attach device to.
654 * @dev: [in] device to be attached.
655 * @dynamic_mapping: [in] calling convention for map/unmap
657 * Returns struct dma_buf_attachment pointer for this attachment. Attachments
658 * must be cleaned up by calling dma_buf_detach().
662 * A pointer to newly created &dma_buf_attachment on success, or a negative
663 * error code wrapped into a pointer on failure.
665 * Note that this can fail if the backing storage of @dmabuf is in a place not
666 * accessible to @dev, and cannot be moved to a more suitable place. This is
667 * indicated with the error code -EBUSY.
669 struct dma_buf_attachment *
670 dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
671 bool dynamic_mapping)
673 struct dma_buf_attachment *attach;
676 if (WARN_ON(!dmabuf || !dev))
677 return ERR_PTR(-EINVAL);
679 attach = kzalloc(sizeof(*attach), GFP_KERNEL);
681 return ERR_PTR(-ENOMEM);
684 attach->dmabuf = dmabuf;
685 attach->dynamic_mapping = dynamic_mapping;
687 if (dmabuf->ops->attach) {
688 ret = dmabuf->ops->attach(dmabuf, attach);
692 dma_resv_lock(dmabuf->resv, NULL);
693 list_add(&attach->node, &dmabuf->attachments);
694 dma_resv_unlock(dmabuf->resv);
696 /* When either the importer or the exporter can't handle dynamic
697 * mappings we cache the mapping here to avoid issues with the
698 * reservation object lock.
700 if (dma_buf_attachment_is_dynamic(attach) !=
701 dma_buf_is_dynamic(dmabuf)) {
702 struct sg_table *sgt;
704 if (dma_buf_is_dynamic(attach->dmabuf))
705 dma_resv_lock(attach->dmabuf->resv, NULL);
707 sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
709 sgt = ERR_PTR(-ENOMEM);
714 if (dma_buf_is_dynamic(attach->dmabuf))
715 dma_resv_unlock(attach->dmabuf->resv);
717 attach->dir = DMA_BIDIRECTIONAL;
727 if (dma_buf_is_dynamic(attach->dmabuf))
728 dma_resv_unlock(attach->dmabuf->resv);
730 dma_buf_detach(dmabuf, attach);
733 EXPORT_SYMBOL_GPL(dma_buf_dynamic_attach);
736 * dma_buf_attach - Wrapper for dma_buf_dynamic_attach
737 * @dmabuf: [in] buffer to attach device to.
738 * @dev: [in] device to be attached.
740 * Wrapper to call dma_buf_dynamic_attach() for drivers which still use a static
743 struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
746 return dma_buf_dynamic_attach(dmabuf, dev, false);
748 EXPORT_SYMBOL_GPL(dma_buf_attach);
751 * dma_buf_detach - Remove the given attachment from dmabuf's attachments list;
752 * optionally calls detach() of dma_buf_ops for device-specific detach
753 * @dmabuf: [in] buffer to detach from.
754 * @attach: [in] attachment to be detached; is free'd after this call.
756 * Clean up a device attachment obtained by calling dma_buf_attach().
758 void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
760 if (WARN_ON(!dmabuf || !attach))
764 if (dma_buf_is_dynamic(attach->dmabuf))
765 dma_resv_lock(attach->dmabuf->resv, NULL);
767 dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
769 if (dma_buf_is_dynamic(attach->dmabuf))
770 dma_resv_unlock(attach->dmabuf->resv);
773 dma_resv_lock(dmabuf->resv, NULL);
774 list_del(&attach->node);
775 dma_resv_unlock(dmabuf->resv);
776 if (dmabuf->ops->detach)
777 dmabuf->ops->detach(dmabuf, attach);
781 EXPORT_SYMBOL_GPL(dma_buf_detach);
784 * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
785 * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
787 * @attach: [in] attachment whose scatterlist is to be returned
788 * @direction: [in] direction of DMA transfer
790 * Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
791 * on error. May return -EINTR if it is interrupted by a signal.
793 * A mapping must be unmapped by using dma_buf_unmap_attachment(). Note that
794 * the underlying backing storage is pinned for as long as a mapping exists,
795 * therefore users/importers should not hold onto a mapping for undue amounts of
798 struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
799 enum dma_data_direction direction)
801 struct sg_table *sg_table;
805 if (WARN_ON(!attach || !attach->dmabuf))
806 return ERR_PTR(-EINVAL);
808 if (dma_buf_attachment_is_dynamic(attach))
809 dma_resv_assert_held(attach->dmabuf->resv);
813 * Two mappings with different directions for the same
814 * attachment are not allowed.
816 if (attach->dir != direction &&
817 attach->dir != DMA_BIDIRECTIONAL)
818 return ERR_PTR(-EBUSY);
823 if (dma_buf_is_dynamic(attach->dmabuf))
824 dma_resv_assert_held(attach->dmabuf->resv);
826 sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
828 sg_table = ERR_PTR(-ENOMEM);
830 if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
831 attach->sgt = sg_table;
832 attach->dir = direction;
837 EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
840 * dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
841 * deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
843 * @attach: [in] attachment to unmap buffer from
844 * @sg_table: [in] scatterlist info of the buffer to unmap
845 * @direction: [in] direction of DMA transfer
847 * This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment().
849 void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
850 struct sg_table *sg_table,
851 enum dma_data_direction direction)
855 if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
858 if (dma_buf_attachment_is_dynamic(attach))
859 dma_resv_assert_held(attach->dmabuf->resv);
861 if (attach->sgt == sg_table)
864 if (dma_buf_is_dynamic(attach->dmabuf))
865 dma_resv_assert_held(attach->dmabuf->resv);
867 attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
869 EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
874 * There are mutliple reasons for supporting CPU access to a dma buffer object:
876 * - Fallback operations in the kernel, for example when a device is connected
877 * over USB and the kernel needs to shuffle the data around first before
878 * sending it away. Cache coherency is handled by braketing any transactions
879 * with calls to dma_buf_begin_cpu_access() and dma_buf_end_cpu_access()
882 * Since for most kernel internal dma-buf accesses need the entire buffer, a
883 * vmap interface is introduced. Note that on very old 32-bit architectures
884 * vmalloc space might be limited and result in vmap calls failing.
887 * void \*dma_buf_vmap(struct dma_buf \*dmabuf)
888 * void dma_buf_vunmap(struct dma_buf \*dmabuf, void \*vaddr)
890 * The vmap call can fail if there is no vmap support in the exporter, or if
891 * it runs out of vmalloc space. Fallback to kmap should be implemented. Note
892 * that the dma-buf layer keeps a reference count for all vmap access and
893 * calls down into the exporter's vmap function only when no vmapping exists,
894 * and only unmaps it once. Protection against concurrent vmap/vunmap calls is
895 * provided by taking the dma_buf->lock mutex.
897 * - For full compatibility on the importer side with existing userspace
898 * interfaces, which might already support mmap'ing buffers. This is needed in
899 * many processing pipelines (e.g. feeding a software rendered image into a
900 * hardware pipeline, thumbnail creation, snapshots, ...). Also, Android's ION
901 * framework already supported this and for DMA buffer file descriptors to
902 * replace ION buffers mmap support was needed.
904 * There is no special interfaces, userspace simply calls mmap on the dma-buf
905 * fd. But like for CPU access there's a need to braket the actual access,
906 * which is handled by the ioctl (DMA_BUF_IOCTL_SYNC). Note that
907 * DMA_BUF_IOCTL_SYNC can fail with -EAGAIN or -EINTR, in which case it must
910 * Some systems might need some sort of cache coherency management e.g. when
911 * CPU and GPU domains are being accessed through dma-buf at the same time.
912 * To circumvent this problem there are begin/end coherency markers, that
913 * forward directly to existing dma-buf device drivers vfunc hooks. Userspace
914 * can make use of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The
915 * sequence would be used like following:
918 * - for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
919 * to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
920 * want (with the new data being consumed by say the GPU or the scanout
922 * - munmap once you don't need the buffer any more
924 * For correctness and optimal performance, it is always required to use
925 * SYNC_START and SYNC_END before and after, respectively, when accessing the
926 * mapped address. Userspace cannot rely on coherent access, even when there
927 * are systems where it just works without calling these ioctls.
929 * - And as a CPU fallback in userspace processing pipelines.
931 * Similar to the motivation for kernel cpu access it is again important that
932 * the userspace code of a given importing subsystem can use the same
933 * interfaces with a imported dma-buf buffer object as with a native buffer
934 * object. This is especially important for drm where the userspace part of
935 * contemporary OpenGL, X, and other drivers is huge, and reworking them to
936 * use a different way to mmap a buffer rather invasive.
938 * The assumption in the current dma-buf interfaces is that redirecting the
939 * initial mmap is all that's needed. A survey of some of the existing
940 * subsystems shows that no driver seems to do any nefarious thing like
941 * syncing up with outstanding asynchronous processing on the device or
942 * allocating special resources at fault time. So hopefully this is good
943 * enough, since adding interfaces to intercept pagefaults and allow pte
944 * shootdowns would increase the complexity quite a bit.
947 * int dma_buf_mmap(struct dma_buf \*, struct vm_area_struct \*,
950 * If the importing subsystem simply provides a special-purpose mmap call to
951 * set up a mapping in userspace, calling do_mmap with dma_buf->file will
952 * equally achieve that for a dma-buf object.
955 static int __dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
956 enum dma_data_direction direction)
958 bool write = (direction == DMA_BIDIRECTIONAL ||
959 direction == DMA_TO_DEVICE);
960 struct dma_resv *resv = dmabuf->resv;
963 /* Wait on any implicit rendering fences */
964 ret = dma_resv_wait_timeout_rcu(resv, write, true,
965 MAX_SCHEDULE_TIMEOUT);
973 * dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
974 * cpu in the kernel context. Calls begin_cpu_access to allow exporter-specific
975 * preparations. Coherency is only guaranteed in the specified range for the
976 * specified access direction.
977 * @dmabuf: [in] buffer to prepare cpu access for.
978 * @direction: [in] length of range for cpu access.
980 * After the cpu access is complete the caller should call
981 * dma_buf_end_cpu_access(). Only when cpu access is braketed by both calls is
982 * it guaranteed to be coherent with other DMA access.
984 * Can return negative error values, returns 0 on success.
986 int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
987 enum dma_data_direction direction)
991 if (WARN_ON(!dmabuf))
994 if (dmabuf->ops->begin_cpu_access)
995 ret = dmabuf->ops->begin_cpu_access(dmabuf, direction);
997 /* Ensure that all fences are waited upon - but we first allow
998 * the native handler the chance to do so more efficiently if it
999 * chooses. A double invocation here will be reasonably cheap no-op.
1002 ret = __dma_buf_begin_cpu_access(dmabuf, direction);
1006 EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);
1009 * dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the
1010 * cpu in the kernel context. Calls end_cpu_access to allow exporter-specific
1011 * actions. Coherency is only guaranteed in the specified range for the
1012 * specified access direction.
1013 * @dmabuf: [in] buffer to complete cpu access for.
1014 * @direction: [in] length of range for cpu access.
1016 * This terminates CPU access started with dma_buf_begin_cpu_access().
1018 * Can return negative error values, returns 0 on success.
1020 int dma_buf_end_cpu_access(struct dma_buf *dmabuf,
1021 enum dma_data_direction direction)
1027 if (dmabuf->ops->end_cpu_access)
1028 ret = dmabuf->ops->end_cpu_access(dmabuf, direction);
1032 EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);
1036 * dma_buf_mmap - Setup up a userspace mmap with the given vma
1037 * @dmabuf: [in] buffer that should back the vma
1038 * @vma: [in] vma for the mmap
1039 * @pgoff: [in] offset in pages where this mmap should start within the
1042 * This function adjusts the passed in vma so that it points at the file of the
1043 * dma_buf operation. It also adjusts the starting pgoff and does bounds
1044 * checking on the size of the vma. Then it calls the exporters mmap function to
1045 * set up the mapping.
1047 * Can return negative error values, returns 0 on success.
1049 int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
1050 unsigned long pgoff)
1052 struct file *oldfile;
1055 if (WARN_ON(!dmabuf || !vma))
1058 /* check if buffer supports mmap */
1059 if (!dmabuf->ops->mmap)
1062 /* check for offset overflow */
1063 if (pgoff + vma_pages(vma) < pgoff)
1066 /* check for overflowing the buffer's size */
1067 if (pgoff + vma_pages(vma) >
1068 dmabuf->size >> PAGE_SHIFT)
1071 /* readjust the vma */
1072 get_file(dmabuf->file);
1073 oldfile = vma->vm_file;
1074 vma->vm_file = dmabuf->file;
1075 vma->vm_pgoff = pgoff;
1077 ret = dmabuf->ops->mmap(dmabuf, vma);
1079 /* restore old parameters on failure */
1080 vma->vm_file = oldfile;
1089 EXPORT_SYMBOL_GPL(dma_buf_mmap);
1092 * dma_buf_vmap - Create virtual mapping for the buffer object into kernel
1093 * address space. Same restrictions as for vmap and friends apply.
1094 * @dmabuf: [in] buffer to vmap
1096 * This call may fail due to lack of virtual mapping address space.
1097 * These calls are optional in drivers. The intended use for them
1098 * is for mapping objects linear in kernel space for high use objects.
1099 * Please attempt to use kmap/kunmap before thinking about these interfaces.
1101 * Returns NULL on error.
1103 void *dma_buf_vmap(struct dma_buf *dmabuf)
1107 if (WARN_ON(!dmabuf))
1110 if (!dmabuf->ops->vmap)
1113 mutex_lock(&dmabuf->lock);
1114 if (dmabuf->vmapping_counter) {
1115 dmabuf->vmapping_counter++;
1116 BUG_ON(!dmabuf->vmap_ptr);
1117 ptr = dmabuf->vmap_ptr;
1121 BUG_ON(dmabuf->vmap_ptr);
1123 ptr = dmabuf->ops->vmap(dmabuf);
1124 if (WARN_ON_ONCE(IS_ERR(ptr)))
1129 dmabuf->vmap_ptr = ptr;
1130 dmabuf->vmapping_counter = 1;
1133 mutex_unlock(&dmabuf->lock);
1136 EXPORT_SYMBOL_GPL(dma_buf_vmap);
1139 * dma_buf_vunmap - Unmap a vmap obtained by dma_buf_vmap.
1140 * @dmabuf: [in] buffer to vunmap
1141 * @vaddr: [in] vmap to vunmap
1143 void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
1145 if (WARN_ON(!dmabuf))
1148 BUG_ON(!dmabuf->vmap_ptr);
1149 BUG_ON(dmabuf->vmapping_counter == 0);
1150 BUG_ON(dmabuf->vmap_ptr != vaddr);
1152 mutex_lock(&dmabuf->lock);
1153 if (--dmabuf->vmapping_counter == 0) {
1154 if (dmabuf->ops->vunmap)
1155 dmabuf->ops->vunmap(dmabuf, vaddr);
1156 dmabuf->vmap_ptr = NULL;
1158 mutex_unlock(&dmabuf->lock);
1160 EXPORT_SYMBOL_GPL(dma_buf_vunmap);
1162 #ifdef CONFIG_DEBUG_FS
1163 static int dma_buf_debug_show(struct seq_file *s, void *unused)
1166 struct dma_buf *buf_obj;
1167 struct dma_buf_attachment *attach_obj;
1168 struct dma_resv *robj;
1169 struct dma_resv_list *fobj;
1170 struct dma_fence *fence;
1172 int count = 0, attach_count, shared_count, i;
1175 ret = mutex_lock_interruptible(&db_list.lock);
1180 seq_puts(s, "\nDma-buf Objects:\n");
1181 seq_printf(s, "%-8s\t%-8s\t%-8s\t%-8s\texp_name\t%-8s\n",
1182 "size", "flags", "mode", "count", "ino");
1184 list_for_each_entry(buf_obj, &db_list.head, list_node) {
1186 ret = dma_resv_lock_interruptible(buf_obj->resv, NULL);
1190 seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\t%08lu\t%s\n",
1192 buf_obj->file->f_flags, buf_obj->file->f_mode,
1193 file_count(buf_obj->file),
1195 file_inode(buf_obj->file)->i_ino,
1196 buf_obj->name ?: "");
1198 robj = buf_obj->resv;
1200 seq = read_seqcount_begin(&robj->seq);
1202 fobj = rcu_dereference(robj->fence);
1203 shared_count = fobj ? fobj->shared_count : 0;
1204 fence = rcu_dereference(robj->fence_excl);
1205 if (!read_seqcount_retry(&robj->seq, seq))
1211 seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
1212 fence->ops->get_driver_name(fence),
1213 fence->ops->get_timeline_name(fence),
1214 dma_fence_is_signaled(fence) ? "" : "un");
1215 for (i = 0; i < shared_count; i++) {
1216 fence = rcu_dereference(fobj->shared[i]);
1217 if (!dma_fence_get_rcu(fence))
1219 seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
1220 fence->ops->get_driver_name(fence),
1221 fence->ops->get_timeline_name(fence),
1222 dma_fence_is_signaled(fence) ? "" : "un");
1223 dma_fence_put(fence);
1227 seq_puts(s, "\tAttached Devices:\n");
1230 list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
1231 seq_printf(s, "\t%s\n", dev_name(attach_obj->dev));
1234 dma_resv_unlock(buf_obj->resv);
1236 seq_printf(s, "Total %d devices attached\n\n",
1240 size += buf_obj->size;
1243 seq_printf(s, "\nTotal %d objects, %zu bytes\n", count, size);
1245 mutex_unlock(&db_list.lock);
1249 mutex_unlock(&db_list.lock);
1253 DEFINE_SHOW_ATTRIBUTE(dma_buf_debug);
1255 static struct dentry *dma_buf_debugfs_dir;
1257 static int dma_buf_init_debugfs(void)
1262 d = debugfs_create_dir("dma_buf", NULL);
1266 dma_buf_debugfs_dir = d;
1268 d = debugfs_create_file("bufinfo", S_IRUGO, dma_buf_debugfs_dir,
1269 NULL, &dma_buf_debug_fops);
1271 pr_debug("dma_buf: debugfs: failed to create node bufinfo\n");
1272 debugfs_remove_recursive(dma_buf_debugfs_dir);
1273 dma_buf_debugfs_dir = NULL;
1280 static void dma_buf_uninit_debugfs(void)
1282 debugfs_remove_recursive(dma_buf_debugfs_dir);
1285 static inline int dma_buf_init_debugfs(void)
1289 static inline void dma_buf_uninit_debugfs(void)
1294 static int __init dma_buf_init(void)
1296 dma_buf_mnt = kern_mount(&dma_buf_fs_type);
1297 if (IS_ERR(dma_buf_mnt))
1298 return PTR_ERR(dma_buf_mnt);
1300 mutex_init(&db_list.lock);
1301 INIT_LIST_HEAD(&db_list.head);
1302 dma_buf_init_debugfs();
1305 subsys_initcall(dma_buf_init);
1307 static void __exit dma_buf_deinit(void)
1309 dma_buf_uninit_debugfs();
1310 kern_unmount(dma_buf_mnt);
1312 __exitcall(dma_buf_deinit);