New subject: [RFC] dma-shared-buf: Add buffer sharing framework

10 Aug 2011

This RFC is aimed at introducing the buffer sharing framework for review.
Since almost all the discussion about buffer sharing objects happened on
linaro-mm-sig list, I am sending it first for review within the list, and
will share it with other lists after first-set of review comments from here.
--
This is the first step in defining a buffer sharing framework.
A new buffer object is added, with hooks to allow for easy sharing of
this buffer object across devices.
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.
The framework allows:
- a new buffer-object to be created, which associates 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 allocator-defined operations.
- the exporter and importer to share the scatterlist using get_ and put_
   operations.
Some file operations are provided as wrappers over the allocator-defined
operations, which allows usage of fops(eg mmap) on the associated 'fd'.
This is based on design suggestions from many people at both the mini-summits,
most notably from Arnd Bergmann arnd@arndb.de, and Rob Clark rob@ti.com.
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.
Signed-off-by: Sumit Semwal sumit.semwal@ti.com
---
 drivers/base/Kconfig    |   10 +++
 drivers/base/Makefile   |    1 +
 drivers/base/dma-buf.c  |  196 +++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dma-buf.h |  105 +++++++++++++++++++++++++
 4 files changed, 312 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 d57e8d0..5398ce8 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -168,4 +168,14 @@ config SYS_HYPERVISOR
    bool
    default n
+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 4c5701c..bd95732 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..e35b385
--- /dev/null
+++ b/drivers/base/dma-buf.c
@@ -0,0 +1,196 @@
+/*
+ * Framework for buffer objects that can be shared across devices/subsystems.
+ *
+ * Copyright(C) 2011 Texas Instruments Inc. All rights reserved.
+ * Author: Sumit Semwal sumit.semwal@ti.com
+ *
+ * Many thanks to linaro-mm-sig list, and specially
+ * Arnd Bergmann arnd@arndb.de and Rob Clark rob@ti.com
+ * 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 int is_dma_buf_file(struct file *);
+
+/* file operation wrappers for dma buf ops */
+static ssize_t dma_buf_read(struct file *file, char __user *buf, size_t size,
+				loff_t *offset)
+{
+	struct dma_buf *dmabuf;
+
+	if (!is_dma_buf_file(file))
+		return -EINVAL;
+
+	dmabuf = file->private_data;
+	return dmabuf->ops->read(dmabuf, buf, size);
+}
+
+static ssize_t dma_buf_write(struct file *file, char __user *buf, size_t size,
+				loff_t *offset)
+{
+	struct dma_buf *dmabuf;
+
+	if (!is_dma_buf_file(file))
+		return -EINVAL;
+
+	dmabuf = file->private_data;
+	return dmabuf->ops->write(dmabuf, buf, size);
+}
+
+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;
+	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,
+	.read		= dma_buf_read,
+	.write		= dma_buf_write,
+	.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 'attach' the allocator specific data and ops to the buffer.
+ *
+ * @priv:	Attach private data of allocator to this buffer
+ * @ops:	Attach allocator-defined dma buf ops to the new buffer.
+ *
+ * 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)
+{
+	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, 0);
+
+	dmabuf->file = file;
+	file->private_data = dmabuf;
+
+	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);
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
new file mode 100644
index 0000000..c22896a
--- /dev/null
+++ b/include/linux/dma-buf.h
@@ -0,0 +1,105 @@
+/*
+ * Header file for dma buffer sharing framework.
+ *
+ * Copyright(C) 2011 Texas Instruments Inc. All rights reserved.
+ * Author: Sumit Semwal sumit.semwal@ti.com
+ *
+ * Many thanks to linaro-mm-sig list, and specially
+ * Arnd Bergmann arnd@arndb.de and Rob Clark rob@ti.com
+ * 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>
+
+struct dma_buf;
+
+/**
+ * struct dma_buf_ops - operations possible on struct dmabuf
+ * @get_scatterlist: returns list of scatter pages allocated, increases
+ *		     usecount of the buffer
+ * @put_scatterlist: decreases usecount of buffer, might deallocate scatter
+ *		     pages
+ * @mmap: map this buffer
+ * @read: read from this buffer
+ * @write: write to this buffer
+ * @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 {
+	/* allow buffer to not be pinned when DMA is not happening */
+	struct scatterlist * (*get_scatterlist)(struct dma_buf *);
+	void (*put_scatterlist)(struct dma_buf *, struct scatterlist *);
+
+	/* allow allocator to mmap/read/write to take care of cache attrib */
+	int (*mmap)(struct dma_buf *, struct vm_area_struct *);
+	ssize_t (*read)(struct dma_buf *, void *, size_t);
+	ssize_t (*write)(struct dma_buf *, void *, size_t);
+	/* 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.
+ * @ops: dma_buf_ops associated with this buffer object
+ * @priv: user specific private data
+ */
+struct dma_buf {
+	struct file *file;
+	struct dma_buf_ops *ops;
+	void *priv;
+};
+
+#ifdef CONFIG_DMA_SHARED_BUFFER
+
+struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops);
+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 *dma_buf_export(void *priv,
+						struct dma_buf_ops *ops)
+{
+	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

    

[RFC] dma-shared-buf: Add buffer sharing framework

Yours, Daniel

Cheers, Daniel

Cheers, Daniel

-Daniel

-Daniel

-Daniel

-Daniel

-Daniel

Cheers, Daniel

--> indicate buffer is no longer to be used by importing device

Cheers, Daniel

-Daniel

-Daniel

Signed-off-by: Sumit Semwal sumit.semwal@ti.com