Subject: [RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism

From: [email-masked] (Konrad Rzeszutek Wilk)
Date: Fri, 2 Dec 2011 12:11:17 -0500

On Fri, Dec 02, 2011 at 02:27:31PM +0530, Sumit Semwal wrote:
> 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:
> - 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 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.
> 
> *OPTIONALLY*: 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.
> 
> 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 <[email-masked]>, Rob Clark <[email-masked]> and
> Daniel Vetter <[email-masked]>.
> 
> The implementation is inspired from proof-of-concept patch-set from
> Tomasz Stanislawski <[email-masked]>, 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 <[email-masked]>
> Signed-off-by: Sumit Semwal <[email-masked]>

You have a clone? You only need one SOB.

> ---
>  drivers/base/Kconfig    |   10 ++
>  drivers/base/Makefile   |    1 +
>  drivers/base/dma-buf.c  |  290 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-buf.h |  176 ++++++++++++++++++++++++++++
>  4 files changed, 477 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..4b9005e
> --- /dev/null
> +++ b/drivers/base/dma-buf.c
> @@ -0,0 +1,290 @@
> +/*
> + * Framework for buffer objects that can be shared across devices/subsystems.
> + *
> + * Copyright(C) 2011 Linaro Limited. All rights reserved.
> + * Author: Sumit Semwal <[email-masked]>

OK, so the SOB should be from @ti.com then.

> + *
> + * Many thanks to linaro-mm-sig list, and specially
> + * Arnd Bergmann <[email-masked]>, Rob Clark <[email-masked]> and
> + * Daniel Vetter <[email-masked]> 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_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;
> +

Should you check if dmabuf is NULL and or dmabuf->ops is NULL too?

Hm, you probably don't need to check for dmabuf, but from
looking at  dma_buf_export one could pass  a NULL for the ops.

> +	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;
> +

No checking here for ops or ops->release?

> +	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;
> +}
> +
> +/**

I don't think the ** is anymore the current kernel doc format.

> + * dma_buf_export - Creates a new dma_buf, and associates an anon file
> + * with this buffer,so it can be exported.

Put a space there.

> + * 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.

"it can" I think the right word is "it will".

> + *
> + */
> +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);

Whoa. Crash the whole kernel b/c of this? No no. You should
use WARN_ON and just return NULL.

> +
> +	dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
> +	if (dmabuf == NULL)
> +		return dmabuf;

Hmm, why not return ERR_PTR(-ENOMEM); ?

> +
> +	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);

_GPL ?

> +
> +
> +/**
> + * 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;
> +

Should you check if dmabuf is NULL first?

> +	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);

GPL?
> +
> +/**
> + * 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);

GPL
> +
> +/**
> + * 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);

Yikes. BUG_ON? Can't you do WARN_ON and continue on without
doing the refcounting?

> +
> +	fput(dmabuf->file);
> +}
> +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 device' should be at the same column as 'struct dma_buf' ..

> +{
> +	struct dma_buf_attachment *attach;
> +	int ret;
> +
> +	BUG_ON(!dmabuf || !dev);

Again, BUG_ON...

> +
> +	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) {

No checking first of dmabuf->ops?

> +		ret = dmabuf->ops->attach(dmabuf, dev, attach);
> +		if (!ret)
> +			goto err_attach;
> +	}
> +	list_add(&attach->node, &dmabuf->attachments);
> +
> +	mutex_unlock(&dmabuf->lock);
> +
> +err_alloc:
> +	return attach;
> +err_attach:
> +	kfree(attach);
> +	mutex_unlock(&dmabuf->lock);
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(dma_buf_attach);

GPL
> +
> +/**
> + * 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);
> +
> +	mutex_unlock(&dmabuf->lock);
> +	kfree(attach);
> +}
> +EXPORT_SYMBOL(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);
> +
> +	BUG_ON(!attach || !attach->dmabuf);
> +
> +	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(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)
> +{
> +	BUG_ON(!attach || !attach->dmabuf || !sg_table);
> +
> +	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(dma_buf_unmap_attachment);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> new file mode 100644
> index 0000000..db4b384
> --- /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 <[email-masked]>
> + *
> + * Many thanks to linaro-mm-sig list, and specially
> + * Arnd Bergmann <[email-masked]>, Rob Clark <[email-masked]> and
> + * Daniel Vetter <[email-masked]> 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
> + * @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]
> + * @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.
> + * @unmap_dma_buf: 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 {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.
> +	 */
> +
> +	/* 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);
> +
> +struct sg_table * dma_buf_map_attachment(struct dma_buf_attachment *,
> +					 enum dma_data_direction);
> +void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *);
> +#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;
> +}
> +
> +static inline struct sg_table * dma_buf_map_attachment(
> +	struct dma_buf_attachment *, enum dma_data_direction)
> +{
> +	return ERR_PTR(-ENODEV);
> +}
> +
> +static inline void dma_buf_unmap_attachment(struct dma_buf_attachment *,
> +						struct sg_table *)
> +{
> +	return;
> +}
> +
> +#endif /* CONFIG_DMA_SHARED_BUFFER */
> +
> +#endif /* __DMA_BUF_H__ */
> -- 
> 1.7.4.1
> 
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