[RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism
InKi Dae
daeinki at gmail.com
Mon Jan 9 01:20:48 EST 2012
2011/12/2 Sumit Semwal <sumit.semwal at 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:
> - 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 <arnd at arndb.de>, Rob Clark <rob at ti.com> and
> Daniel Vetter <daniel at ffwll.ch>.
>
> The implementation is inspired from proof-of-concept patch-set from
> Tomasz Stanislawski <t.stanislaws at 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 at linaro.org>
> Signed-off-by: Sumit Semwal <sumit.semwal at ti.com>
> ---
> 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 <sumit.semwal at ti.com>
> + *
> + * Many thanks to linaro-mm-sig list, and specially
> + * Arnd Bergmann <arnd at arndb.de>, Rob Clark <rob at ti.com> and
> + * Daniel Vetter <daniel at 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_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct dma_buf *dmabuf;
> +
> + if (!is_dma_buf_file(file))
> + return -EINVAL;
> +
> + dmabuf = file->private_data;
> +
> + if (!dmabuf->ops->mmap)
> + return -EINVAL;
> +
> + return dmabuf->ops->mmap(dmabuf, vma);
> +}
> +
> +static int dma_buf_release(struct inode *inode, struct file *file)
> +{
> + struct dma_buf *dmabuf;
> +
> + if (!is_dma_buf_file(file))
> + return -EINVAL;
> +
> + dmabuf = file->private_data;
> +
> + dmabuf->ops->release(dmabuf);
> + kfree(dmabuf);
> + return 0;
> +}
> +
> +static const struct file_operations dma_buf_fops = {
> + .mmap = dma_buf_mmap,
> + .release = dma_buf_release,
> +};
> +
> +/*
> + * is_dma_buf_file - Check if struct file* is associated with dma_buf
> + */
> +static inline int is_dma_buf_file(struct file *file)
> +{
> + return file->f_op == &dma_buf_fops;
> +}
> +
> +/**
> + * dma_buf_export - Creates a new dma_buf, and associates an anon file
> + * with this buffer,so it can be exported.
> + * Also connect the allocator specific data and ops to the buffer.
> + *
> + * @priv: [in] Attach private data of allocator to this buffer
> + * @ops: [in] Attach allocator-defined dma buf ops to the new buffer.
> + * @flags: [in] mode flags for the file.
> + *
> + * Returns, on success, a newly created dma_buf object, which wraps the
> + * supplied private data and operations for dma_buf_ops. On failure to
> + * allocate the dma_buf object, it can return NULL.
> + *
> + */
> +struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
> + int flags)
> +{
> + struct dma_buf *dmabuf;
> + struct file *file;
> +
> + BUG_ON(!priv || !ops);
> +
> + dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
> + if (dmabuf == NULL)
> + return dmabuf;
> +
> + dmabuf->priv = priv;
> + dmabuf->ops = ops;
> +
> + file = anon_inode_getfile("dmabuf", &dma_buf_fops, dmabuf, flags);
> +
> + dmabuf->file = file;
> +
> + mutex_init(&dmabuf->lock);
> + INIT_LIST_HEAD(&dmabuf->attachments);
> +
> + return dmabuf;
> +}
> +EXPORT_SYMBOL(dma_buf_export);
> +
> +
> +/**
> + * dma_buf_fd - returns a file descriptor for the given dma_buf
> + * @dmabuf: [in] pointer to dma_buf for which fd is required.
> + *
> + * On success, returns an associated 'fd'. Else, returns error.
> + */
> +int dma_buf_fd(struct dma_buf *dmabuf)
> +{
> + int error, fd;
> +
> + if (!dmabuf->file)
> + return -EINVAL;
> +
> + error = get_unused_fd_flags(0);
> + if (error < 0)
> + return error;
> + fd = error;
> +
> + fd_install(fd, dmabuf->file);
> +
> + return fd;
> +}
> +EXPORT_SYMBOL(dma_buf_fd);
> +
> +/**
> + * dma_buf_get - returns the dma_buf structure related to an fd
> + * @fd: [in] fd associated with the dma_buf to be returned
> + *
> + * On success, returns the dma_buf structure associated with an fd; uses
> + * file's refcounting done by fget to increase refcount. returns ERR_PTR
> + * otherwise.
> + */
> +struct dma_buf *dma_buf_get(int fd)
> +{
> + struct file *file;
> +
> + file = fget(fd);
> +
> + if (!file)
> + return ERR_PTR(-EBADF);
> +
> + if (!is_dma_buf_file(file)) {
> + fput(file);
> + return ERR_PTR(-EINVAL);
> + }
> +
> + return file->private_data;
> +}
> +EXPORT_SYMBOL(dma_buf_get);
> +
> +/**
> + * dma_buf_put - decreases refcount of the buffer
> + * @dmabuf: [in] buffer to reduce refcount of
> + *
> + * Uses file's refcounting done implicitly by fput()
> + */
> +void dma_buf_put(struct dma_buf *dmabuf)
> +{
> + BUG_ON(!dmabuf->file);
> +
> + fput(dmabuf->file);
> +}
> +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 dma_buf_attachment *attach;
> + int ret;
> +
> + BUG_ON(!dmabuf || !dev);
> +
> + 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);
> +
> +err_alloc:
> + return attach;
> +err_attach:
> + kfree(attach);
> + mutex_unlock(&dmabuf->lock);
> + return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL(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)
> +{
> + 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 <sumit.semwal at ti.com>
> + *
> + * Many thanks to linaro-mm-sig list, and specially
> + * Arnd Bergmann <arnd at arndb.de>, Rob Clark <rob at ti.com> and
> + * Daniel Vetter <daniel at 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 - 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.
> + */
I has test dmabuf based drm gem module for exynos and I found one problem.
you can refer to this test repository:
http://git.infradead.org/users/kmpark/linux-samsung/shortlog/refs/heads/exynos-drm-dmabuf
at this repository, I added some exception codes for resource release
in addition to Dave's patch sets.
let's suppose we use dmabuf based vb2 and drm gem with physically
continuous memory(no IOMMU) and we try to share allocated buffer
between them(v4l2 and drm driver).
1. request memory allocation through drm gem interface.
2. request DRM_SET_PRIME ioctl with the gem handle to get a fd to the
gem object.
- internally, private gem based dmabuf moudle calls drm_buf_export()
to register allocated gem object to fd.
3. request qbuf with the fd(got from 2) and DMABUF type to set the
buffer to v4l2 based device.
- internally, vb2 plug in module gets a buffer to the fd and then
calls dmabuf->ops->map_dmabuf() callback to get the sg table
containing physical memory info to the gem object. and then the
physical memory info would be copied to vb2_xx_buf object.
for DMABUF feature for v4l2 and videobuf2 framework, you can refer to
this repository:
git://github.com/robclark/kernel-omap4.git drmplane-dmabuf
after that, if v4l2 driver want to release vb2_xx_buf object with
allocated memory region by user request, how should we do?. refcount
to vb2_xx_buf is dependent on videobuf2 framework. so when vb2_xx_buf
object is released videobuf2 framework don't know who is using the
physical memory region. so this physical memory region is released and
when drm driver tries to access the region or to release it also, a
problem would be induced.
for this problem, I added get_shared_cnt() callback to dma-buf.h but
I'm not sure that this is good way. maybe there may be better way.
if there is any missing point, please let me know.
Thanks.
> +
> + /* 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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