[Linaro-mm-sig] [RFC v3] dma-buf: Add buffer sharing framework
Sumit Semwal
sumit.semwal at linaro.org
Sat Oct 8 07:47:30 UTC 2011
Hello Everyone,
Thanks a bunch on your reviews for v1 and v2; may I please request you to do
a review of this one as well, before I post it to the upstream lists?
Thanks and best regards,
~Sumit.
On 30 September 2011 18:19, Sumit Semwal <sumit.semwal at linaro.org> wrote:
> Patch available on git.linaro.org feature tree as
>
> version 3:
> http://git.linaro.org/gitweb?p=people/sumitsemwal/linux-3.x.git;a=shortlog;h=refs/heads/dma-buf-v3
>
> Best regards,
> ~Sumit.
>
> On 30 September 2011 18:12, 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
>>
>>
>
>
> --
>
> Thanks and regards,
>
> Sumit Semwal
>
> Linaro Kernel Engineer - Graphics working group
>
> Linaro.org <http://www.linaro.org/>* **│ *Open source software for ARM
> SoCs****
>
> Follow *Linaro: *Facebook <http://www.facebook.com/pages/Linaro> | Twitter<http://twitter.com/#%21/linaroorg>
> | Blog <http://www.linaro.org/linaro-blog/>
>
>
--
Thanks and regards,
Sumit Semwal
Linaro Kernel Engineer - Graphics working group
Linaro.org <http://www.linaro.org/>* **│ *Open source software for ARM SoCs*
***
Follow *Linaro: *Facebook <http://www.facebook.com/pages/Linaro> |
Twitter<http://twitter.com/#%21/linaroorg>
| Blog <http://www.linaro.org/linaro-blog/>
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