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SubjectRe: [PATCH 1/3] dma-buf: Introduce dma buffer sharing mechanism
From
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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