[Linaro-mm-sig] [RFC v3] dma-buf: Add buffer sharing framework
Clark, Rob
rob at ti.com
Sun Oct 9 20:43:39 UTC 2011
hmm, random though..
should we define CPU_PREP/CPU_FINI type ioctl's?
At least in the GStreamer case, we could cache the userspace mmap'ing,
and use the extra ioctls so the kernel side would know when cache
clean/invalidate is needed. That would be a bit more efficient than
forcing userspace to map/unmap all the time, and could hook into
sync-objects of the allocator in cases where you have CPU access after
GPU renders to a buffer..
BR,
-R
On Fri, Sep 30, 2011 at 7:42 AM, Sumit Semwal <sumit.semwal at ti.com> wrote:
> [Hopefully the last version to linaro-mm-sig before I send it out to
> upstream linux lists]
>
> This is the first step in defining a buffer sharing framework.
> A new dma_buf buffer object is added, with hooks to allow for easy sharing of
> this buffer object across devices.
>
> The framework allows:
> - a new buffer-object to be created with fixed size.
> - different devices to 'attach' themselves to this buffer, to facilitate
> backing storage negotiation, using dma_buf_attach() API.
> - association of a file pointer with each user-buffer and associated
> allocator-defined operations on that buffer. This operation is called the
> 'export' operation.
> - this exported buffer-object to be shared with the other entity by asking for
> its 'file-descriptor (fd)', and sharing the fd across.
> - a received fd to get the buffer object back, where it can be accessed using
> the associated exporter-defined operations.
> - the exporter and user to share the scatterlist using get_scatterlist and
> put_scatterlist operations.
>
> Atleast one 'dma_buf_attach()' call is required to be made prior to calling the
> get_scatterlist() operation.
>
> Couple of building blocks in get_scatterlist() are added to ease introduction
> of sync'ing across exporter and users, and late allocation by the exporter.
>
> mmap() file operation is provided for the associated 'fd', as wrapper over the
> optional allocator defined mmap(), to be used by devices that might need one.
>
> Please read documentation added in this patch for more details.
>
> The idea was first mooted at the Linaro memory management mini-summit in
> Budapest in May 2011, as part of multiple things needed for a 'unified memory
> management framework'. It took a more concrete shape at Linaro memory-management
> mini-summit in Cambridge, Aug 2011.
>
> This is based on design suggestions from many people at both the mini-summits,
> most notably from Arnd Bergmann <arnd at arndb.de>, Rob Clark <rob at ti.com> and
> Daniel Vetter <daniel at ffwll.ch>.
>
> The implementation is inspired from proof-of-concept patch-set from
> Tomasz Stanislawski <t.stanislaws at samsung.com>, who demonstrated buffer sharing
> between two v4l2 devices.
>
> ------
> v3:
> - added dma_buf to dma_attachment and updated {get,put}_scatterlist accordingly.
> - added locking mechanism in struct dma_buf, and used around attach-detach APIs.
> - dmabuf->ops->attach/detach made optional.
> - removed dma_buf_attr_flags and replaced dma_buf_optye with dma_data_direction.
> - made dma_buf->ops const in struct dma_buf.
> - updated comments for get_scatterlist.
> - added documentation.
>
> v2:
> - added attach() / detach() dma_buf_ops, and dma_buf_attach(),dma_buf_detach().
> - added handling of list of attachment in the dma_buf central API itself.
> - corrected copyright information.
>
> v1: initial RFC.
>
> Signed-off-by: Sumit Semwal <sumit.semwal at linaro.org>
> Signed-off-by: Sumit Semwal <sumit.semwal at ti.com>
> ---
> Documentation/dma-buf-sharing.txt | 210 ++++++++++++++++++++++++++++++++
> drivers/base/Kconfig | 10 ++
> drivers/base/Makefile | 1 +
> drivers/base/dma-buf.c | 242 +++++++++++++++++++++++++++++++++++++
> include/linux/dma-buf.h | 162 +++++++++++++++++++++++++
> 5 files changed, 625 insertions(+), 0 deletions(-)
> create mode 100644 Documentation/dma-buf-sharing.txt
> create mode 100644 drivers/base/dma-buf.c
> create mode 100644 include/linux/dma-buf.h
>
> diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
> new file mode 100644
> index 0000000..4da6644
> --- /dev/null
> +++ b/Documentation/dma-buf-sharing.txt
> @@ -0,0 +1,210 @@
> + 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 B 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,
> +- optionally, provides mmap capability for drivers that need it.
> +
> +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.
> +
> +
> +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,
> + int flags)
> +
> + If this succeeds, dma_buf_export allocates a dma_buf structure, and returns a
> + pointer to the same. It also associates an anon 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
> + anon 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 anon 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 book-keeping bits related to keeping
> + the list of all attachments to a buffer.
> +
> +Till 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->ops->get_scatterlist operation. Atleast
> + one attach to the buffer should have happened before get_scatterlist can be
> + called.
> +
> + Interface: [member of struct dma_buf_ops]
> + struct scatterlist * (*get_scatterlist)(struct dma_buf_attachment *,
> + enum dma_data_direction,
> + int* nents);
> +
> + It is one of the buffer operations that must be implemented by the exporter.
> + It should return the 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.
> +
> +
> +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->ops->put_scatterlist() operation.
> +
> + Interface:
> + void (*put_scatterlist)(struct dma_buf_attachment *, struct scatterlist *,
> + int nents);
> +
> + put_scatterlist signifies the end-of-dma for the attachment provided.
> +
> +
> +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 {get,put}_scatterlist 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 {get,put}_scatterlist 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
> + After
> + - atleast one get_scatterlist has happened,
> + - and the backing storage has been allocated for this buffer,
> + If 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
> + get_scatterlist till all outstanding access is completed (as signalled by
> + put_scatterlist).
> + Once all ongoing access is completed, the exporter could potentially move
> + the buffer to the stricter backing-storage, and then allow further
> + {get,put}_scatterlist operations from any buffer-user from the migrated
> + backing-storage.
> +
> + If the exporter cannot fulfill 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
> + get_scatterlist has been called, it simply returns an error.
> +
> +- mmap file operation
> + An mmap() file operation is provided for the fd associated with the buffer.
> + If the exporter defines an mmap operation, the mmap() fop calls this to allow
> + mmap for devices that might need it; if not, it 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 21cf46f..07d8095 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -174,4 +174,14 @@ config SYS_HYPERVISOR
>
> source "drivers/base/regmap/Kconfig"
>
> +config DMA_SHARED_BUFFER
> + bool "Buffer framework to be shared between drivers"
> + default n
> + depends on ANON_INODES
> + 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 99a375a..d0df046 100644
> --- a/drivers/base/Makefile
> +++ b/drivers/base/Makefile
> @@ -8,6 +8,7 @@ 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 0000000..58c51a0
> --- /dev/null
> +++ b/drivers/base/dma-buf.c
> @@ -0,0 +1,242 @@
> +/*
> + * Framework for buffer objects that can be shared across devices/subsystems.
> + *
> + * Copyright(C) 2011 Linaro Limited. All rights reserved.
> + * Author: Sumit Semwal <sumit.semwal at ti.com>
> + *
> + * Many thanks to linaro-mm-sig list, and specially
> + * Arnd Bergmann <arnd at arndb.de>, Rob Clark <rob at ti.com> and
> + * Daniel Vetter <daniel at 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>
> +
> +static inline int is_dma_buf_file(struct file *);
> +
> +static int dma_buf_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct dma_buf *dmabuf;
> +
> + if (!is_dma_buf_file(file))
> + return -EINVAL;
> +
> + dmabuf = file->private_data;
> +
> + if (!dmabuf->ops->mmap)
> + return -EINVAL;
> +
> + return dmabuf->ops->mmap(dmabuf, vma);
> +}
> +
> +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 = {
> + .mmap = dma_buf_mmap,
> + .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.
> + * @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 failure to
> + * allocate the dma_buf object, it can return NULL.
> + *
> + */
> +struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
> + int flags)
> +{
> + struct dma_buf *dmabuf;
> + struct file *file;
> +
> + BUG_ON(!priv || !ops);
> +
> + dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
> + if (dmabuf == NULL)
> + return dmabuf;
> +
> + dmabuf->priv = priv;
> + dmabuf->ops = ops;
> +
> + 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(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->file)
> + return -EINVAL;
> +
> + error = get_unused_fd_flags(0);
> + if (error < 0)
> + return error;
> + fd = error;
> +
> + fd_install(fd, dmabuf->file);
> +
> + return fd;
> +}
> +EXPORT_SYMBOL(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(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)
> +{
> + BUG_ON(!dmabuf->file);
> +
> + fput(dmabuf->file);
> +
> + return;
> +}
> +EXPORT_SYMBOL(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 NULL.
> + *
> + */
> +struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> + struct device *dev)
> +{
> + struct dma_buf_attachment *attach;
> + int ret;
> +
> + BUG_ON(!dmabuf || !dev);
> +
> + mutex_lock(&dmabuf->lock);
> +
> + attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
> + if (attach == NULL)
> + goto err_alloc;
> +
> + attach->dev = dev;
> + if (dmabuf->ops->attach) {
> + ret = dmabuf->ops->attach(dmabuf, dev, attach);
> + if (!ret)
> + goto err_attach;
> + }
> + list_add(&attach->node, &dmabuf->attachments);
> +
> +err_alloc:
> + mutex_unlock(&dmabuf->lock);
> + return attach;
> +err_attach:
> + kfree(attach);
> + mutex_unlock(&dmabuf->lock);
> + return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(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)
> +{
> + BUG_ON(!dmabuf || !attach);
> +
> + mutex_lock(&dmabuf->lock);
> + list_del(&attach->node);
> + if (dmabuf->ops->detach)
> + dmabuf->ops->detach(dmabuf, attach);
> +
> + kfree(attach);
> + mutex_unlock(&dmabuf->lock);
> + return;
> +}
> +EXPORT_SYMBOL(dma_buf_detach);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> new file mode 100644
> index 0000000..5bdf16a
> --- /dev/null
> +++ b/include/linux/dma-buf.h
> @@ -0,0 +1,162 @@
> +/*
> + * Header file for dma buffer sharing framework.
> + *
> + * Copyright(C) 2011 Linaro Limited. All rights reserved.
> + * Author: Sumit Semwal <sumit.semwal at ti.com>
> + *
> + * Many thanks to linaro-mm-sig list, and specially
> + * Arnd Bergmann <arnd at arndb.de>, Rob Clark <rob at ti.com> and
> + * Daniel Vetter <daniel at 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 - holds device-buffer attachment data
> + * @dmabuf: buffer for this attachment.
> + * @dev: device attached to the buffer.
> + * @node: list_head to allow manipulation of list of dma_buf_attachment.
> + * @priv: exporter-specific attachment data.
> + */
> +struct dma_buf_attachment {
> + struct dma_buf *dmabuf;
> + struct device *dev;
> + struct list_head node;
> + void *priv;
> +};
> +
> +/**
> + * struct dma_buf_ops - operations possible on struct dma_buf
> + * @create: creates a struct dma_buf of a fixed size. Actual allocation
> + * does not happen here.
> + * @attach: 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. [optional]
> + * @detach: detach a given device from this buffer. [optional]
> + * @get_scatterlist: 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.
> + * @put_scatterlist: decreases usecount of buffer, might deallocate scatter
> + * pages.
> + * @mmap: memory map this buffer - optional.
> + * @release: release this buffer; to be called after the last dma_buf_put.
> + * @sync_sg_for_cpu: sync the sg list for cpu.
> + * @sync_sg_for_device: synch the sg list for device.
> + */
> +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 {get,put}_scatterlist below, any specific buffer attributes
> + * required should get added to device_dma_parameters accessible
> + * via dev->dma_params.
> + */
> + struct scatterlist * (*get_scatterlist)(struct dma_buf_attachment *,
> + enum dma_data_direction,
> + int *nents);
> + void (*put_scatterlist)(struct dma_buf_attachment *,
> + struct scatterlist *,
> + int nents);
> + /* TODO: Add interruptible and interruptible_timeout versions */
> +
> + /* allow mmap optionally for devices that need it */
> + int (*mmap)(struct dma_buf *, struct vm_area_struct *);
> + /* after final dma_buf_put() */
> + void (*release)(struct dma_buf *);
> +
> + /* allow allocator to take care of cache ops */
> + void (*sync_sg_for_cpu) (struct dma_buf *, struct device *);
> + void (*sync_sg_for_device)(struct dma_buf *, struct device *);
> +};
> +
> +/**
> + * struct dma_buf - shared buffer object
> + * @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: user specific private data
> + */
> +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;
> +};
> +
> +#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, 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);
> +
> +#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,
> + 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;
> +}
> +#endif /* CONFIG_DMA_SHARED_BUFFER */
> +
> +#endif /* __DMA_BUF_H__ */
> --
> 1.7.4.1
>
>
More information about the Linaro-mm-sig
mailing list