[1/3] 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>
---
 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
  

2011/12/26 Sumit Semwal <sumit.semwal@ti.com>:
> 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>
> ---
>  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;

how about having sg_table here also? like this, struct sg_table *sgt;
now dmabuf->priv could have duplicated values.
I know that a private buffer object is set to dmabuf->priv when
dma_buf_export function is called. but when  xxx_acquire_dmabuf
callback of vb2 side is called dmabuf->priv would have sg_table object
returned from dmabuf->ops->map_dma_buf() again to release the sg_table
with dmabuf->ops->unmap_dma_buf(). I'm not sure that this situation
could induce some problem but anyway confusing.

> +       /* mutex to serialize list manipulation and other ops */
> +       struct mutex lock;
> +       void *priv;
> +};
> +
> +/**
> + * struct dma_buf_attachment - holds device-buffer attachment data
> + * @dmabuf: buffer for this attachment.
> + * @dev: device attached to the buffer.
> + * @node: list of dma_buf_attachment.
> + * @priv: exporter specific attachment data.
> + *
> + * This structure holds the attachment information between the dma_buf buffer
> + * and its user device(s). The list contains one attachment struct per device
> + * attached to the buffer.
> + */
> +struct dma_buf_attachment {
> +       struct dma_buf *dmabuf;
> +       struct device *dev;
> +       struct list_head node;
> +       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,
> +                       size_t size, 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,
> +                                               size_t size, 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 *attach, enum dma_data_direction write)
> +{
> +       return ERR_PTR(-ENODEV);
> +}
> +
> +static inline void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> +                                               struct sg_table *sg)
> +{
> +       return;
> +}
> +
> +#endif /* CONFIG_DMA_SHARED_BUFFER */
> +
> +#endif /* __DMA_BUF_H__ */
> --
> 1.7.5.4
>
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Hi Summit,

Sorry for the late review. I know that this code is now in mainline, but I 
still have a couple of comments. I'll send patches if you agree with them.

On Monday 26 December 2011 10:23:15 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:
> - 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>
> ---
>  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
> 

[snip]

> 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 @@

[snip]

> +/**
> + * 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->ops will never but NULL, but (see below)

> +	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);

[snip]

> +/**
> + * 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))

you still check dmabuf->ops here, as well as in several places below. 
Shouldn't these checks be removed ?

> +		return ERR_PTR(-EINVAL);
> +
> +	attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
> +	if (attach == NULL)
> +		goto err_alloc;

What about returning ERR_PTR(-ENOMEM) directly here ?

> +
> +	mutex_lock(&dmabuf->lock);
> +
> +	attach->dev = dev;
> +	attach->dmabuf = dmabuf;

These two lines can be moved before mutex_lock().

> +	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);
  

On Fri, Jan 20, 2012 at 6:53 PM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> Hi Summit,
>
> Sorry for the late review. I know that this code is now in mainline, but I
> still have a couple of comments. I'll send patches if you agree with them.
Hi Laurent,

Thanks for your review; apologies for being late in replying - I was
OoO for last couple of days.
>
> On Monday 26 December 2011 10:23:15 Sumit Semwal wrote:
<snip>
>>
>
> [snip]
>
>> 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 @@
>
> [snip]
>
>> +/**
>> + * 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->ops will never but NULL, but (see below)
>
<snip>
>> +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))
>
> you still check dmabuf->ops here, as well as in several places below.
> Shouldn't these checks be removed ?
You're right - these can be removed.
>
>> +             return ERR_PTR(-EINVAL);
>> +
>> +     attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
>> +     if (attach == NULL)
>> +             goto err_alloc;
>
> What about returning ERR_PTR(-ENOMEM) directly here ?
>
Right; we can do that.
>> +
>> +     mutex_lock(&dmabuf->lock);
>> +
>> +     attach->dev = dev;
>> +     attach->dmabuf = dmabuf;
>
> These two lines can be moved before mutex_lock().
>
:) Yes - thanks for catching this.
<snip>
> --
> Regards,
>
> Laurent Pinchart

Let me know if you'd send patches for these, or should I just go ahead
and correct.

Best regards,
~Sumit.
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Hi Sumit,

On 12/26/2011 10:23 AM, 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:
> - 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.
>

[snip]

> +/**
> + * struct dma_buf_attachment - holds device-buffer attachment data
> + * @dmabuf: buffer for this attachment.
> + * @dev: device attached to the buffer.
> + * @node: list of dma_buf_attachment.
> + * @priv: exporter specific attachment data.
> + *
> + * This structure holds the attachment information between the dma_buf buffer
> + * and its user device(s). The list contains one attachment struct per device
> + * attached to the buffer.
> + */
> +struct dma_buf_attachment {
> +	struct dma_buf *dmabuf;
> +	struct device *dev;
> +	struct list_head node;
> +	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,
> +			size_t size, 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 *);

I think that you should add enum dma_data_direction as an argument
unmap function. It was mentioned that the dma_buf_attachment should keep
cached and mapped sg_table for performance reasons. The field
dma_buf_attachment::priv seams to be a natural place to keep this sg_table.
To map a buffer the exporter calls dma_map_sg. It needs dma direction
as an argument. The problem is that dma_unmap_sg also needs this
argument but dma direction is not available neither in
dma_buf_unmap_attachment nor in unmap callback. Therefore the exporter
is forced to embed returned sg_table into a bigger structure where dma 
direction is remembered. Refer to function vb2_dc_dmabuf_ops_map at
link below as an example:

http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/43793/focus=43797

Regards,
Tomasz Stanislawski
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On Wed, Jan 25, 2012 at 06:02:41PM +0100, Tomasz Stanislawski wrote:
> Hi Sumit,
> 
> On 12/26/2011 10:23 AM, 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:
> >- 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.
> >
> 
> [snip]
> 
> >+/**
> >+ * struct dma_buf_attachment - holds device-buffer attachment data
> >+ * @dmabuf: buffer for this attachment.
> >+ * @dev: device attached to the buffer.
> >+ * @node: list of dma_buf_attachment.
> >+ * @priv: exporter specific attachment data.
> >+ *
> >+ * This structure holds the attachment information between the dma_buf buffer
> >+ * and its user device(s). The list contains one attachment struct per device
> >+ * attached to the buffer.
> >+ */
> >+struct dma_buf_attachment {
> >+	struct dma_buf *dmabuf;
> >+	struct device *dev;
> >+	struct list_head node;
> >+	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,
> >+			size_t size, 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 *);
> 
> I think that you should add enum dma_data_direction as an argument
> unmap function. It was mentioned that the dma_buf_attachment should keep
> cached and mapped sg_table for performance reasons. The field
> dma_buf_attachment::priv seams to be a natural place to keep this sg_table.
> To map a buffer the exporter calls dma_map_sg. It needs dma direction
> as an argument. The problem is that dma_unmap_sg also needs this
> argument but dma direction is not available neither in
> dma_buf_unmap_attachment nor in unmap callback. Therefore the exporter
> is forced to embed returned sg_table into a bigger structure where
> dma direction is remembered. Refer to function vb2_dc_dmabuf_ops_map
> at

Oops, makes sense. I've totally overlooked that we need to pass in the dma
direction also for the unmap call to the dma subsystem. Sumit, can you
stitch together that small patch?
-Daniel
  

On Thu, Jan 26, 2012 at 1:37 AM, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Wed, Jan 25, 2012 at 06:02:41PM +0100, Tomasz Stanislawski wrote:
>> Hi Sumit,
>>
>> On 12/26/2011 10:23 AM, Sumit Semwal wrote:
>> >This is the first step in defining a dma buffer sharing mechanism.
>> >
>> [snip]
>>
>> >+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 *);
>>
>> I think that you should add enum dma_data_direction as an argument
>> unmap function. It was mentioned that the dma_buf_attachment should keep
>> cached and mapped sg_table for performance reasons. The field
>> dma_buf_attachment::priv seams to be a natural place to keep this sg_table.
>> To map a buffer the exporter calls dma_map_sg. It needs dma direction
>> as an argument. The problem is that dma_unmap_sg also needs this
>> argument but dma direction is not available neither in
>> dma_buf_unmap_attachment nor in unmap callback. Therefore the exporter
>> is forced to embed returned sg_table into a bigger structure where
>> dma direction is remembered. Refer to function vb2_dc_dmabuf_ops_map
>> at
>
> Oops, makes sense. I've totally overlooked that we need to pass in the dma
> direction also for the unmap call to the dma subsystem. Sumit, can you
> stitch together that small patch?

Right, of course. I will do that by tomorrow; it is a bank holiday
today here in India, so.

regards,
~Sumit.
> -Daniel
> --
> Daniel Vetter
> Mail: daniel@ffwll.ch
> Mobile: +41 (0)79 365 57 48
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Hi Sumit,

On Wednesday 25 January 2012 14:56:52 Semwal, Sumit wrote:
> On Fri, Jan 20, 2012 at 6:53 PM, Laurent Pinchart wrote:
> > Hi Summit,
> > 
> > Sorry for the late review. I know that this code is now in mainline, but
> > I still have a couple of comments. I'll send patches if you agree with
> > them.
> 
> Hi Laurent,
> 
> Thanks for your review; apologies for being late in replying - I was
> OoO for last couple of days.

No worries.

[snip]

> Let me know if you'd send patches for these, or should I just go ahead and
> correct.

I'll send patches.

Another small comment. The map_dma_buf operation is defined as

        struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *,
                                                enum dma_data_direction);

If we want to let exporters cache the sg_table we should return a const struct 
sg_table *. unmap_dma_buf will then take a const pointer as well, which would 
need to be cast to a non-const pointer internally. What's your opinion on that 
?