This is the first step in defining a dma buffer sharing mechanism.

A new buffer object dma_buf is added, with operations and API to allow easy
sharing of this buffer object across devices.

The framework allows:
- creation of a buffer object, its association with a file pointer, and
? associated allocator-defined operations on that buffer. This operation is
? called the 'export' operation.
- different devices to 'attach' themselves to this exported buffer object, to
?facilitate backing storage negotiation, using dma_buf_attach() API.
- the 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 associated with this buffer
? object using map_dma_buf and unmap_dma_buf operations.

Atleast one 'attach()' call is required to be made prior to calling the
map_dma_buf() operation.

Couple of building blocks in map_dma_buf() are added to ease introduction
of sync'ing across exporter and users, and late allocation by the exporter.

For this first version, this framework will work with certain conditions:
- *ONLY* exporter will be allowed to mmap to userspace (outside of this
? framework - mmap is not a buffer object operation),
- currently, *ONLY* users that do not need CPU access to the buffer are
? allowed.

More details are there in the documentation patch.

This is based on design suggestions from many people at the mini-summits[1],
most notably from Arnd Bergmann [off-list ref], Rob Clark [off-list ref] and
Daniel Vetter [off-list ref].

The implementation is inspired from proof-of-concept patch-set from
Tomasz Stanislawski [off-list ref], who demonstrated buffer sharing
between two v4l2 devices. [2]

[1]: https://wiki.linaro.org/OfficeofCTO/MemoryManagement
[2]: http://lwn.net/Articles/454389

Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Sumit Semwal <redacted>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-and-Tested-by: Rob Clark [off-list ref]
---
?drivers/base/Kconfig ? ?| ? 10 ++
?drivers/base/Makefile ? | ? ?1 +
?drivers/base/dma-buf.c ?| ?291 +++++++++++++++++++++++++++++++++++++++++++++++
?include/linux/dma-buf.h | ?176 ++++++++++++++++++++++++++++
?4 files changed, 478 insertions(+), 0 deletions(-)
?create mode 100644 drivers/base/dma-buf.c
?create mode 100644 include/linux/dma-buf.h

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 21cf46f..8a0e87f 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
+ ? ? ? select 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..e38ad24
--- /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 0000000..f8ac076
--- /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;