[RFC v2] dma-buf: Add buffer sharing framework - Linaro-mm-sig

13 Sep 2011

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 importer to share the scatterlist using get_scatterlist and
   put_scatterlist operations.
Atleast one 'attach()' call is required to be made prior to calling the
buffer_map() callback.
Couple of building blocks in get_scatterlist() are added to ease introduction
of sync'ing across exporter and importers, and late allocation by the exporter.
Optionally, mmap() file operation is provided for the associated 'fd', as
wrapper over the allocator defined mmap()[optional], to be used by devices that
might need one.
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@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.
------
v1: initial RFC.
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.
Signed-off-by: Sumit Semwal sumit.semwal@linaro.org
Signed-off-by: Sumit Semwal sumit.semwal@ti.com
---
 drivers/base/Kconfig    |   10 ++
 drivers/base/Makefile   |    1 +
 drivers/base/dma-buf.c  |  224 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h |  179 +++++++++++++++++++++++++++++++++++++
 4 files changed, 414 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..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..8936da7
--- /dev/null
+++ b/drivers/base/dma-buf.c
@@ -0,0 +1,224 @@
+/*
+ * 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>
+
+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;
+
+	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; calls the
+ * 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;
+
+	BUG_ON(!dmabuf || !dev);
+
+	attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
+	if (attach == NULL)
+		return attach;
+
+	dmabuf->ops->attach(dmabuf, dev, attach);
+	list_add(&attach->node, &dmabuf->attachments);
+
+	return attach;
+}
+EXPORT_SYMBOL(dma_buf_attach);
+
+/**
+ * dma_buf_detach - Remove the given attachment from dmabuf's attachments list;
+ * 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);
+
+	list_del(&attach->node);
+	dmabuf->ops->detach(dmabuf, attach);
+
+	kfree(attach);
+	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..2894b45
--- /dev/null
+++ b/include/linux/dma-buf.h
@@ -0,0 +1,179 @@
+/*
+ * 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>
+
+struct dma_buf;
+
+/**
+ * enum dma_buf_optype - Used to denote the operation for which
+ * get_scatterlist() is called. This will help in implementing a wait(op)
+ * for sync'ing.
+ * @DMA_BUF_OP_READ: read operation will be done on this scatterlist
+ * @DMA_BUF_OP_WRITE: write operation will be done on this scatterlist
+ */
+enum dma_buf_optype {
+	DMA_BUF_OP_READ		= (1 << 0),
+	DMA_BUF_OP_WRITE	= (1 << 1),
+	DMA_BUF_OP_MAX,
+};
+
+/**
+ * enum dma_buf_attr_flags - Defines the attributes for this buffer. This
+ * can allow 'late backing of buffer' based on first get_scatterlist() call.
+ * @DMA_BUF_ATTR_CONTIG: Contiguous buffer
+ * @DMA_BUF_ATTR_DISCONTIG: Discontiguous buffer
+ * @DMA_BUF_ATTR_CUSTOM: Platform specific buffer; should evolve into some
+ * attributes that define buffers on given specific platform
+ */
+enum dma_buf_attr_flags {
+	DMA_BUF_ATTR_CONTIG,
+	DMA_BUF_ATTR_DISCONTIG,
+	DMA_BUF_ATTR_CUSTOM,
+	DMA_BUF_ATTR_MAX,
+};
+
+/**
+ * struct dma_buf_attachment - holds device-buffer attachment data
+ * @node: list_head to allow manipulation of list of dma_buf_attachment.
+ * @dev: device attached to the buffer.
+ * @priv: exporter-specific attachment data.
+ */
+struct dma_buf_attachment {
+	struct list_head node;
+	struct device *dev;
+	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.
+ * @detach: detach a given device from this buffer.
+ * @get_scatterlist: returns list of scatter pages allocated, increases
+ *		     usecount of the buffer. Requires atleast one attach to be
+ *		     called before.
+ * @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 {
+	void (*attach)(struct dma_buf *, struct device *,
+			struct dma_buf_attachment *);
+
+	void (*detach)(struct dma_buf *, struct dma_buf_attachment *);
+
+	struct scatterlist * (*get_scatterlist)(struct dma_buf *,
+						struct dma_buf_attachment *,
+						enum dma_buf_optype,
+						enum dma_buf_attr_flags);
+	void (*put_scatterlist)(struct dma_buf *, struct dma_buf_attachment *,
+						struct scatterlist *);
+
+	/* 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;
+	struct dma_buf_ops *ops;
+	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

    