dma-buf: Introduce dma buffer sharing mechanism

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 <arnd@arndb.de>, Rob Clark <rob@ti.com> and
Daniel Vetter <daniel@ffwll.ch>.

The implementation is inspired from proof-of-concept patch-set from
Tomasz Stanislawski <t.stanislaws@samsung.com>, 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 <sumit.semwal@ti.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-and-Tested-by: Rob Clark <rob.clark@linaro.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

3 files changed, 302 insertions, 0 deletions

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);