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* Header file for dma buffer sharing framework.
* Copyright(C) 2011 Linaro Limited. All rights reserved.
* Author: Sumit Semwal <>
* Many thanks to linaro-mm-sig list, and specially
* Arnd Bergmann <>, Rob Clark <> and
* Daniel Vetter <> 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 <>.
#ifndef __DMA_BUF_H__
#define __DMA_BUF_H__
#include <linux/file.h>
#include <linux/err.h>
#include <linux/scatterlist.h>
#include <linux/list.h>
#include <linux/dma-mapping.h>
#include <linux/fs.h>
#include <linux/dma-fence.h>
#include <linux/wait.h>
struct device;
struct dma_buf;
struct dma_buf_attachment;
* struct dma_buf_ops - operations possible on struct dma_buf
* @map_atomic: [optional] maps a page from the buffer into kernel address
* space, users may not block until the subsequent unmap call.
* This callback must not sleep.
* @unmap_atomic: [optional] unmaps a atomically mapped page from the buffer.
* This Callback must not sleep.
* @map: [optional] maps a page from the buffer into kernel address space.
* @unmap: [optional] unmaps a page from the buffer.
* @vmap: [optional] creates a virtual mapping for the buffer into kernel
* address space. Same restrictions as for vmap and friends apply.
* @vunmap: [optional] unmaps a vmap from the buffer
struct dma_buf_ops {
* @attach:
* This is called from dma_buf_attach() to make sure that a given
* & can access the provided &dma_buf. Exporters
* which support buffer objects in special locations like VRAM or
* device-specific carveout areas should check whether the buffer could
* be move to system memory (or directly accessed by the provided
* device), and otherwise need to fail the attach operation.
* The exporter should also in general check whether the current
* allocation fullfills the DMA constraints of the new device. If this
* is not the case, and the allocation cannot be moved, it should also
* fail the attach operation.
* Any exporter-private housekeeping data can be stored in the
* &dma_buf_attachment.priv pointer.
* This callback is optional.
* Returns:
* 0 on success, negative error code on failure. It might return -EBUSY
* to signal that backing storage is already allocated and incompatible
* with the requirements of requesting device.
int (*attach)(struct dma_buf *, struct dma_buf_attachment *);
* @detach:
* This is called by dma_buf_detach() to release a &dma_buf_attachment.
* Provided so that exporters can clean up any housekeeping for an
* &dma_buf_attachment.
* This callback is optional.
void (*detach)(struct dma_buf *, struct dma_buf_attachment *);
* @map_dma_buf:
* This is called by dma_buf_map_attachment() and is used to map a
* shared &dma_buf into device address space, and it is mandatory. It
* can only be called if @attach has been called successfully. This
* essentially pins the DMA buffer into place, and it cannot be moved
* any more
* This call may sleep, e.g. when the backing storage first needs to be
* allocated, or moved to a location suitable for all currently attached
* devices.
* Note that any specific buffer attributes required for this function
* should get added to device_dma_parameters accessible via
* &device.dma_params from the &dma_buf_attachment. The @attach callback
* should also check these constraints.
* If this is being called for the first time, the exporter can now
* choose to scan through the list of attachments for this buffer,
* collate the requirements of the attached devices, and choose an
* appropriate backing storage for the buffer.
* Based on enum dma_data_direction, it might be possible to have
* multiple users accessing at the same time (for reading, maybe), or
* any other kind of sharing that the exporter might wish to make
* available to buffer-users.
* Returns:
* A &sg_table scatter list of or the backing storage of the DMA buffer,
* already mapped into the device address space of the &device attached
* with the provided &dma_buf_attachment.
* On failure, returns a negative error value wrapped into a pointer.
* May also return -EINTR when a signal was received while being
* blocked.
struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *,
enum dma_data_direction);
* @unmap_dma_buf:
* This is called by dma_buf_unmap_attachment() and should unmap and
* release the &sg_table allocated in @map_dma_buf, and it is mandatory.
* It should also unpin the backing storage if this is the last mapping
* of the DMA buffer, it the exporter supports backing storage
* migration.
void (*unmap_dma_buf)(struct dma_buf_attachment *,
struct sg_table *,
enum dma_data_direction);
/* TODO: Add try_map_dma_buf version, to return immed with -EBUSY
* if the call would block.
* @release:
* Called after the last dma_buf_put to release the &dma_buf, and
* mandatory.
void (*release)(struct dma_buf *);
* @begin_cpu_access:
* This is called from dma_buf_begin_cpu_access() and allows the
* exporter to ensure that the memory is actually available for cpu
* access - the exporter might need to allocate or swap-in and pin the
* backing storage. The exporter also needs to ensure that cpu access is
* coherent for the access direction. The direction can be used by the
* exporter to optimize the cache flushing, i.e. access with a different
* direction (read instead of write) might return stale or even bogus
* data (e.g. when the exporter needs to copy the data to temporary
* storage).
* This callback is optional.
* FIXME: This is both called through the DMA_BUF_IOCTL_SYNC command
* from userspace (where storage shouldn't be pinned to avoid handing
* de-factor mlock rights to userspace) and for the kernel-internal
* users of the various kmap interfaces, where the backing storage must
* be pinned to guarantee that the atomic kmap calls can succeed. Since
* there's no in-kernel users of the kmap interfaces yet this isn't a
* real problem.
* Returns:
* 0 on success or a negative error code on failure. This can for
* example fail when the backing storage can't be allocated. Can also
* return -ERESTARTSYS or -EINTR when the call has been interrupted and
* needs to be restarted.
int (*begin_cpu_access)(struct dma_buf *, enum dma_data_direction);
* @end_cpu_access:
* This is called from dma_buf_end_cpu_access() when the importer is
* done accessing the CPU. The exporter can use this to flush caches and
* unpin any resources pinned in @begin_cpu_access.
* The result of any dma_buf kmap calls after end_cpu_access is
* undefined.
* This callback is optional.
* Returns:
* 0 on success or a negative error code on failure. Can return
* -ERESTARTSYS or -EINTR when the call has been interrupted and needs
* to be restarted.
int (*end_cpu_access)(struct dma_buf *, enum dma_data_direction);
void *(*map)(struct dma_buf *, unsigned long);
void (*unmap)(struct dma_buf *, unsigned long, void *);
* @mmap:
* This callback is used by the dma_buf_mmap() function
* Note that the mapping needs to be incoherent, userspace is expected
* to braket CPU access using the DMA_BUF_IOCTL_SYNC interface.
* Because dma-buf buffers have invariant size over their lifetime, the
* dma-buf core checks whether a vma is too large and rejects such
* mappings. The exporter hence does not need to duplicate this check.
* Drivers do not need to check this themselves.
* If an exporter needs to manually flush caches and hence needs to fake
* coherency for mmap support, it needs to be able to zap all the ptes
* pointing at the backing storage. Now linux mm needs a struct
* address_space associated with the struct file stored in vma->vm_file
* to do that with the function unmap_mapping_range. But the dma_buf
* framework only backs every dma_buf fd with the anon_file struct file,
* i.e. all dma_bufs share the same file.
* Hence exporters need to setup their own file (and address_space)
* association by setting vma->vm_file and adjusting vma->vm_pgoff in
* the dma_buf mmap callback. In the specific case of a gem driver the
* exporter could use the shmem file already provided by gem (and set
* vm_pgoff = 0). Exporters can then zap ptes by unmapping the
* corresponding range of the struct address_space associated with their
* own file.
* This callback is optional.
* Returns:
* 0 on success or a negative error code on failure.
int (*mmap)(struct dma_buf *, struct vm_area_struct *vma);
void *(*vmap)(struct dma_buf *);
void (*vunmap)(struct dma_buf *, void *vaddr);
* struct dma_buf - shared buffer object
* @size: size of the buffer
* @file: file pointer used for sharing buffers across, and for refcounting.
* @attachments: list of dma_buf_attachment that denotes all devices attached.
* @ops: dma_buf_ops associated with this buffer object.
* @lock: used internally to serialize list manipulation, attach/detach and vmap/unmap
* @vmapping_counter: used internally to refcnt the vmaps
* @vmap_ptr: the current vmap ptr if vmapping_counter > 0
* @exp_name: name of the exporter; useful for debugging.
* @owner: pointer to exporter module; used for refcounting when exporter is a
* kernel module.
* @list_node: node for dma_buf accounting and debugging.
* @priv: exporter specific private data for this buffer object.
* @resv: reservation object linked to this dma-buf
* @poll: for userspace poll support
* @cb_excl: for userspace poll support
* @cb_shared: for userspace poll support
* This represents a shared buffer, created by calling dma_buf_export(). The
* userspace representation is a normal file descriptor, which can be created by
* calling dma_buf_fd().
* Shared dma buffers are reference counted using dma_buf_put() and
* get_dma_buf().
* Device DMA access is handled by the separate &struct dma_buf_attachment.
struct dma_buf {
size_t size;
struct file *file;
struct list_head attachments;
const struct dma_buf_ops *ops;
struct mutex lock;
unsigned vmapping_counter;
void *vmap_ptr;
const char *exp_name;
struct module *owner;
struct list_head list_node;
void *priv;
struct reservation_object *resv;
/* poll support */
wait_queue_head_t poll;
struct dma_buf_poll_cb_t {
struct dma_fence_cb cb;
wait_queue_head_t *poll;
__poll_t active;
} cb_excl, cb_shared;
* struct dma_buf_attachment - holds device-buffer attachment data
* @dmabuf: buffer for this attachment.
* @dev: device attached to the buffer.
* @node: list of dma_buf_attachment.
* @priv: exporter specific attachment data.
* This structure holds the attachment information between the dma_buf buffer
* and its user device(s). The list contains one attachment struct per device
* attached to the buffer.
* An attachment is created by calling dma_buf_attach(), and released again by
* calling dma_buf_detach(). The DMA mapping itself needed to initiate a
* transfer is created by dma_buf_map_attachment() and freed again by calling
* dma_buf_unmap_attachment().
struct dma_buf_attachment {
struct dma_buf *dmabuf;
struct device *dev;
struct list_head node;
void *priv;
* struct dma_buf_export_info - holds information needed to export a dma_buf
* @exp_name: name of the exporter - useful for debugging.
* @owner: pointer to exporter module - used for refcounting kernel module
* @ops: Attach allocator-defined dma buf ops to the new buffer
* @size: Size of the buffer
* @flags: mode flags for the file
* @resv: reservation-object, NULL to allocate default one
* @priv: Attach private data of allocator to this buffer
* This structure holds the information required to export the buffer. Used
* with dma_buf_export() only.
struct dma_buf_export_info {
const char *exp_name;
struct module *owner;
const struct dma_buf_ops *ops;
size_t size;
int flags;
struct reservation_object *resv;
void *priv;
* DEFINE_DMA_BUF_EXPORT_INFO - helper macro for exporters
* @name: export-info name
* DEFINE_DMA_BUF_EXPORT_INFO macro defines the &struct dma_buf_export_info,
* zeroes it out and pre-populates exp_name in it.
struct dma_buf_export_info name = { .exp_name = KBUILD_MODNAME, \
.owner = THIS_MODULE }
* get_dma_buf - convenience wrapper for get_file.
* @dmabuf: [in] pointer to dma_buf
* Increments the reference count on the dma-buf, needed in case of drivers
* that either need to create additional references to the dmabuf on the
* kernel side. For example, an exporter that needs to keep a dmabuf ptr
* so that subsequent exports don't create a new dmabuf.
static inline void get_dma_buf(struct dma_buf *dmabuf)
struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
struct device *dev);
void dma_buf_detach(struct dma_buf *dmabuf,
struct dma_buf_attachment *dmabuf_attach);
struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info);
int dma_buf_fd(struct dma_buf *dmabuf, int flags);
struct dma_buf *dma_buf_get(int fd);
void dma_buf_put(struct dma_buf *dmabuf);
struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *,
enum dma_data_direction);
void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
enum dma_data_direction);
int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
enum dma_data_direction dir);
int dma_buf_end_cpu_access(struct dma_buf *dma_buf,
enum dma_data_direction dir);
void *dma_buf_kmap(struct dma_buf *, unsigned long);
void dma_buf_kunmap(struct dma_buf *, unsigned long, void *);
int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
unsigned long);
void *dma_buf_vmap(struct dma_buf *);
void dma_buf_vunmap(struct dma_buf *, void *vaddr);
#endif /* __DMA_BUF_H__ */