Merge branch 'dma-buf-merge' of git://people.freedesktop.org/~airlied/linux

* 'dma-buf-merge' of git://people.freedesktop.org/~airlied/linux:
  dma-buf: mark EXPERIMENTAL for 1st release.
  dma-buf: Documentation for buffer sharing framework
  dma-buf: Introduce dma buffer sharing mechanism

5 files changed, 703 insertions, 0 deletions

diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
new file mode 100644
index 00000000000..510eab32f39
--- /dev/null
+++ b/Documentation/dma-buf-sharing.txt
@@ -0,0 +1,224 @@
+                    DMA Buffer Sharing API Guide
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+                            Sumit Semwal
+                <sumit dot semwal at linaro dot org>
+                 <sumit dot semwal at ti dot com>
+
+This document serves as a guide to device-driver writers on what is the dma-buf
+buffer sharing API, how to use it for exporting and using shared buffers.
+
+Any device driver which wishes to be a part of DMA buffer sharing, can do so as
+either the 'exporter' of buffers, or the 'user' of buffers.
+
+Say a driver A wants to use buffers created by driver B, then we call B as the
+exporter, and A as buffer-user.
+
+The exporter
+- implements and manages operations[1] for the buffer
+- allows other users to share the buffer by using dma_buf sharing APIs,
+- manages the details of buffer allocation,
+- decides about the actual backing storage where this allocation happens,
+- takes care of any migration of scatterlist - for all (shared) users of this
+   buffer,
+
+The buffer-user
+- is one of (many) sharing users of the buffer.
+- doesn't need to worry about how the buffer is allocated, or where.
+- needs a mechanism to get access to the scatterlist that makes up this buffer
+   in memory, mapped into its own address space, so it can access the same area
+   of memory.
+
+*IMPORTANT*: [see https://lkml.org/lkml/2011/12/20/211 for more details]
+For this first version, A buffer shared using the dma_buf sharing API:
+- *may* be exported to user space using "mmap" *ONLY* by exporter, outside of
+   this framework.
+- may be used *ONLY* by importers that do not need CPU access to the buffer.
+
+The dma_buf buffer sharing API usage contains the following steps:
+
+1. Exporter announces that it wishes to export a buffer
+2. Userspace gets the file descriptor associated with the exported buffer, and
+   passes it around to potential buffer-users based on use case
+3. Each buffer-user 'connects' itself to the buffer
+4. When needed, buffer-user requests access to the buffer from exporter
+5. When finished with its use, the buffer-user notifies end-of-DMA to exporter
+6. when buffer-user is done using this buffer completely, it 'disconnects'
+   itself from the buffer.
+
+
+1. Exporter's announcement of buffer export
+
+   The buffer exporter announces its wish to export a buffer. In this, it
+   connects its own private buffer data, provides implementation for operations
+   that can be performed on the exported dma_buf, and flags for the file
+   associated with this buffer.
+
+   Interface:
+      struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
+                                     size_t size, int flags)
+
+   If this succeeds, dma_buf_export allocates a dma_buf structure, and returns a
+   pointer to the same. It also associates an anonymous file with this buffer,
+   so it can be exported. On failure to allocate the dma_buf object, it returns
+   NULL.
+
+2. Userspace gets a handle to pass around to potential buffer-users
+
+   Userspace entity requests for a file-descriptor (fd) which is a handle to the
+   anonymous file associated with the buffer. It can then share the fd with other
+   drivers and/or processes.
+
+   Interface:
+      int dma_buf_fd(struct dma_buf *dmabuf)
+
+   This API installs an fd for the anonymous file associated with this buffer;
+   returns either 'fd', or error.
+
+3. Each buffer-user 'connects' itself to the buffer
+
+   Each buffer-user now gets a reference to the buffer, using the fd passed to
+   it.
+
+   Interface:
+      struct dma_buf *dma_buf_get(int fd)
+
+   This API will return a reference to the dma_buf, and increment refcount for
+   it.
+
+   After this, the buffer-user needs to attach its device with the buffer, which
+   helps the exporter to know of device buffer constraints.
+
+   Interface:
+      struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
+                                                struct device *dev)
+
+   This API returns reference to an attachment structure, which is then used
+   for scatterlist operations. It will optionally call the 'attach' dma_buf
+   operation, if provided by the exporter.
+
+   The dma-buf sharing framework does the bookkeeping bits related to managing
+   the list of all attachments to a buffer.
+
+Until this stage, the buffer-exporter has the option to choose not to actually
+allocate the backing storage for this buffer, but wait for the first buffer-user
+to request use of buffer for allocation.
+
+
+4. When needed, buffer-user requests access to the buffer
+
+   Whenever a buffer-user wants to use the buffer for any DMA, it asks for
+   access to the buffer using dma_buf_map_attachment API. At least one attach to
+   the buffer must have happened before map_dma_buf can be called.
+
+   Interface:
+      struct sg_table * dma_buf_map_attachment(struct dma_buf_attachment *,
+                                         enum dma_data_direction);
+
+   This is a wrapper to dma_buf->ops->map_dma_buf operation, which hides the
+   "dma_buf->ops->" indirection from the users of this interface.
+
+   In struct dma_buf_ops, map_dma_buf is defined as
+      struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *,
+                                                enum dma_data_direction);
+
+   It is one of the buffer operations that must be implemented by the exporter.
+   It should return the sg_table containing scatterlist for this buffer, mapped
+   into caller's address space.
+
+   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.
+
+   map_dma_buf() operation can return -EINTR if it is interrupted by a signal.
+
+
+5. When finished, the buffer-user notifies end-of-DMA to exporter
+
+   Once the DMA for the current buffer-user is over, it signals 'end-of-DMA' to
+   the exporter using the dma_buf_unmap_attachment API.
+
+   Interface:
+      void dma_buf_unmap_attachment(struct dma_buf_attachment *,
+                                    struct sg_table *);
+
+   This is a wrapper to dma_buf->ops->unmap_dma_buf() operation, which hides the
+   "dma_buf->ops->" indirection from the users of this interface.
+
+   In struct dma_buf_ops, unmap_dma_buf is defined as
+      void (*unmap_dma_buf)(struct dma_buf_attachment *, struct sg_table *);
+
+   unmap_dma_buf signifies the end-of-DMA for the attachment provided. Like
+   map_dma_buf, this API also must be implemented by the exporter.
+
+
+6. when buffer-user is done using this buffer, it 'disconnects' itself from the
+   buffer.
+
+   After the buffer-user has no more interest in using this buffer, it should
+   disconnect itself from the buffer:
+
+   - it first detaches itself from the buffer.
+
+   Interface:
+      void dma_buf_detach(struct dma_buf *dmabuf,
+                          struct dma_buf_attachment *dmabuf_attach);
+
+   This API removes the attachment from the list in dmabuf, and optionally calls
+   dma_buf->ops->detach(), if provided by exporter, for any housekeeping bits.
+
+   - Then, the buffer-user returns the buffer reference to exporter.
+
+   Interface:
+     void dma_buf_put(struct dma_buf *dmabuf);
+
+   This API then reduces the refcount for this buffer.
+
+   If, as a result of this call, the refcount becomes 0, the 'release' file
+   operation related to this fd is called. It calls the dmabuf->ops->release()
+   operation in turn, and frees the memory allocated for dmabuf when exported.
+
+NOTES:
+- Importance of attach-detach and {map,unmap}_dma_buf operation pairs
+   The attach-detach calls allow the exporter to figure out backing-storage
+   constraints for the currently-interested devices. This allows preferential
+   allocation, and/or migration of pages across different types of storage
+   available, if possible.
+
+   Bracketing of DMA access with {map,unmap}_dma_buf operations is essential
+   to allow just-in-time backing of storage, and migration mid-way through a
+   use-case.
+
+- Migration of backing storage if needed
+   If after
+   - at least one map_dma_buf has happened,
+   - and the backing storage has been allocated for this buffer,
+   another new buffer-user intends to attach itself to this buffer, it might
+   be allowed, if possible for the exporter.
+
+   In case it is allowed by the exporter:
+    if the new buffer-user has stricter 'backing-storage constraints', and the
+    exporter can handle these constraints, the exporter can just stall on the
+    map_dma_buf until all outstanding access is completed (as signalled by
+    unmap_dma_buf).
+    Once all users have finished accessing and have unmapped this buffer, the
+    exporter could potentially move the buffer to the stricter backing-storage,
+    and then allow further {map,unmap}_dma_buf operations from any buffer-user
+    from the migrated backing-storage.
+
+   If the exporter cannot fulfil the backing-storage constraints of the new
+   buffer-user device as requested, dma_buf_attach() would return an error to
+   denote non-compatibility of the new buffer-sharing request with the current
+   buffer.
+
+   If the exporter chooses not to allow an attach() operation once a
+   map_dma_buf() API has been called, it simply returns an error.
+
+References:
+[1] struct dma_buf_ops in include/linux/dma-buf.h
+[2] All interfaces mentioned above defined in include/linux/dma-buf.h
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 21cf46f4524..e95c67edb2c 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -174,4 +174,15 @@ config SYS_HYPERVISOR
 
 source "drivers/base/regmap/Kconfig"
 
+config DMA_SHARED_BUFFER
+        bool "Buffer framework to be shared between drivers"
+        default n
+        select ANON_INODES
+        depends on EXPERIMENTAL
+        help
+          This option enables the framework for buffer-sharing between
+          multiple drivers. A buffer is associated with a file using driver
+          APIs extension; the file's descriptor can then be passed on to other
+          driver.
+
 endmenu
diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 1334d893b56..2c8272dd93c 100644
--- a/drivers/base/Makefile
+++ b/drivers/base/Makefile
@@ -9,6 +9,7 @@ obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
 obj-y                   += power/
 obj-$(CONFIG_HAS_DMA)   += dma-mapping.o
 obj-$(CONFIG_HAVE_GENERIC_DMA_COHERENT) += dma-coherent.o
+obj-$(CONFIG_DMA_SHARED_BUFFER) += dma-buf.o
 obj-$(CONFIG_ISA)       += isa.o
 obj-$(CONFIG_FW_LOADER) += firmware_class.o
 obj-$(CONFIG_NUMA)      += node.o
diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
new file mode 100644
index 00000000000..e38ad243b4b
--- /dev/null
+++ b/drivers/base/dma-buf.c
@@ -0,0 +1,291 @@
+/*
+ * 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/anon_inodes.h>
+#include <linux/export.h>
+
+static inline int is_dma_buf_file(struct file *);
+
+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;
+
+        dmabuf->ops->release(dmabuf);
+        kfree(dmabuf);
+        return 0;
+}
+
+static const struct file_operations dma_buf_fops = {
+        .release        = dma_buf_release,
+};
+
+/*
+ * 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;
+}
+
+/**
+ * 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.
+ *
+ * @priv:       [in]    Attach private data of allocator to this buffer
+ * @ops:        [in]    Attach allocator-defined dma buf ops to the new buffer.
+ * @size:       [in]    Size of the buffer
+ * @flags:      [in]    mode flags for the file.
+ *
+ * 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.
+ *
+ */
+struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
+                                size_t size, int flags)
+{
+        struct dma_buf *dmabuf;
+        struct file *file;
+
+        if (WARN_ON(!priv || !ops
+                          || !ops->map_dma_buf
+                          || !ops->unmap_dma_buf
+                          || !ops->release)) {
+                return ERR_PTR(-EINVAL);
+        }
+
+        dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
+        if (dmabuf == NULL)
+                return ERR_PTR(-ENOMEM);
+
+        dmabuf->priv = priv;
+        dmabuf->ops = ops;
+        dmabuf->size = size;
+
+        file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf, flags);
+
+        dmabuf->file = file;
+
+        mutex_init(&dmabuf->lock);
+        INIT_LIST_HEAD(&dmabuf->attachments);
+
+        return dmabuf;
+}
+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.
+ *
+ * On success, returns an associated 'fd'. Else, returns error.
+ */
+int dma_buf_fd(struct dma_buf *dmabuf)
+{
+        int error, fd;
+
+        if (!dmabuf || !dmabuf->file)
+                return -EINVAL;
+
+        error = get_unused_fd();
+        if (error < 0)
+                return error;
+        fd = error;
+
+        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()
+ */
+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 * for this attachment; may return negative
+ * error codes.
+ *
+ */
+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 || !dmabuf->ops))
+                return ERR_PTR(-EINVAL);
+
+        attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
+        if (attach == NULL)
+                goto err_alloc;
+
+        mutex_lock(&dmabuf->lock);
+
+        attach->dev = dev;
+        attach->dmabuf = dmabuf;
+        if (dmabuf->ops->attach) {
+                ret = dmabuf->ops->attach(dmabuf, dev, attach);
+                if (ret)
+                        goto err_attach;
+        }
+        list_add(&attach->node, &dmabuf->attachments);
+
+        mutex_unlock(&dmabuf->lock);
+        return attach;
+
+err_alloc:
+        return ERR_PTR(-ENOMEM);
+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.
+ *
+ */
+void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
+{
+        if (WARN_ON(!dmabuf || !attach || !dmabuf->ops))
+                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; may return NULL
+ * or ERR_PTR.
+ *
+ */
+struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
+                                        enum dma_data_direction direction)
+{
+        struct sg_table *sg_table = ERR_PTR(-EINVAL);
+
+        might_sleep();
+
+        if (WARN_ON(!attach || !attach->dmabuf || !attach->dmabuf->ops))
+                return ERR_PTR(-EINVAL);
+
+        mutex_lock(&attach->dmabuf->lock);
+        if (attach->dmabuf->ops->map_dma_buf)
+                sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
+        mutex_unlock(&attach->dmabuf->lock);
+
+        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
+ *
+ */
+void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
+                                struct sg_table *sg_table)
+{
+        if (WARN_ON(!attach || !attach->dmabuf || !sg_table
+                            || !attach->dmabuf->ops))
+                return;
+
+        mutex_lock(&attach->dmabuf->lock);
+        if (attach->dmabuf->ops->unmap_dma_buf)
+                attach->dmabuf->ops->unmap_dma_buf(attach, sg_table);
+        mutex_unlock(&attach->dmabuf->lock);
+
+}
+EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
new file mode 100644
index 00000000000..f8ac076afa5
--- /dev/null
+++ b/include/linux/dma-buf.h
@@ -0,0 +1,176 @@
+/*
+ * Header file for dma buffer sharing framework.
+ *
+ * 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/>.
+ */
+#ifndef __DMA_BUF_H__
+#define __DMA_BUF_H__
+
+#include <linux/file.h>
+#include <linux/err.h>
+#include <linux/device.h>
+#include <linux/scatterlist.h>
+#include <linux/list.h>
+#include <linux/dma-mapping.h>
+
+struct dma_buf;
+struct dma_buf_attachment;
+
+/**
+ * struct dma_buf_ops - operations possible on struct dma_buf
+ * @attach: [optional] allows different devices to 'attach' themselves to the
+ *          given buffer. It might return -EBUSY to signal that backing storage
+ *          is already allocated and incompatible with the requirements
+ *          of requesting device.
+ * @detach: [optional] detach a given device from this buffer.
+ * @map_dma_buf: returns list of scatter pages allocated, increases usecount
+ *               of the buffer. Requires atleast one attach to be called
+ *               before. Returned sg list should already be mapped into
+ *               _device_ address space. This call may sleep. May also return
+ *               -EINTR. Should return -EINVAL if attach hasn't been called yet.
+ * @unmap_dma_buf: decreases usecount of buffer, might deallocate scatter
+ *                 pages.
+ * @release: release this buffer; to be called after the last dma_buf_put.
+ */
+struct dma_buf_ops {
+        int (*attach)(struct dma_buf *, struct device *,
+                        struct dma_buf_attachment *);
+
+        void (*detach)(struct dma_buf *, struct dma_buf_attachment *);
+
+        /* For {map,unmap}_dma_buf below, any specific buffer attributes
+         * required should get added to device_dma_parameters accessible
+         * via dev->dma_params.
+         */
+        struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *,
+                                                enum dma_data_direction);
+        void (*unmap_dma_buf)(struct dma_buf_attachment *,
+                                                struct sg_table *);
+        /* TODO: Add try_map_dma_buf version, to return immed with -EBUSY
+         * if the call would block.
+         */
+
+        /* after final dma_buf_put() */
+        void (*release)(struct dma_buf *);
+
+};
+
+/**
+ * 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.
+ * @priv: exporter specific private data for this buffer object.
+ */
+struct dma_buf {
+        size_t size;
+        struct file *file;
+        struct list_head attachments;
+        const struct dma_buf_ops *ops;
+        /* mutex to serialize list manipulation and other ops */
+        struct mutex lock;
+        void *priv;
+};
+
+/**
+ * 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.
+ */
+struct dma_buf_attachment {
+        struct dma_buf *dmabuf;
+        struct device *dev;
+        struct list_head node;
+        void *priv;
+};
+
+#ifdef CONFIG_DMA_SHARED_BUFFER
+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(void *priv, struct dma_buf_ops *ops,
+                        size_t size, int flags);
+int dma_buf_fd(struct dma_buf *dmabuf);
+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 *);
+#else
+
+static inline struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
+                                                        struct device *dev)
+{
+        return ERR_PTR(-ENODEV);
+}
+
+static inline void dma_buf_detach(struct dma_buf *dmabuf,
+                                  struct dma_buf_attachment *dmabuf_attach)
+{
+        return;
+}
+
+static inline struct dma_buf *dma_buf_export(void *priv,
+                                                struct dma_buf_ops *ops,
+                                                size_t size, int flags)
+{
+        return ERR_PTR(-ENODEV);
+}
+
+static inline int dma_buf_fd(struct dma_buf *dmabuf)
+{
+        return -ENODEV;
+}
+
+static inline struct dma_buf *dma_buf_get(int fd)
+{
+        return ERR_PTR(-ENODEV);
+}
+
+static inline void dma_buf_put(struct dma_buf *dmabuf)
+{
+        return;
+}
+
+static inline struct sg_table *dma_buf_map_attachment(
+        struct dma_buf_attachment *attach, enum dma_data_direction write)
+{
+        return ERR_PTR(-ENODEV);
+}
+
+static inline void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
+                                                struct sg_table *sg)
+{
+        return;
+}
+
+#endif /* CONFIG_DMA_SHARED_BUFFER */
+
+#endif /* __DMA_BUF_H__ */