diff options
| -rw-r--r-- | Documentation/dma-buf-sharing.txt | 224 | ||||
| -rw-r--r-- | drivers/base/Kconfig | 11 | ||||
| -rw-r--r-- | drivers/base/Makefile | 1 | ||||
| -rw-r--r-- | drivers/base/dma-buf.c | 291 | ||||
| -rw-r--r-- | include/linux/dma-buf.h | 176 |
5 files changed, 703 insertions, 0 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt new file mode 100644 index 00000000000..510eab32f39 --- /dev/null +++ b/Documentation/dma-buf-sharing.txt @@ -0,0 +1,224 @@ + DMA Buffer Sharing API Guide + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + + Sumit Semwal + <sumit dot semwal at linaro dot org> + <sumit dot semwal at ti dot com> + +This document serves as a guide to device-driver writers on what is the dma-buf +buffer sharing API, how to use it for exporting and using shared buffers. + +Any device driver which wishes to be a part of DMA buffer sharing, can do so as +either the 'exporter' of buffers, or the 'user' of buffers. + +Say a driver A wants to use buffers created by driver B, then we call B as the +exporter, and A as buffer-user. + +The exporter +- implements and manages operations[1] for the buffer +- allows other users to share the buffer by using dma_buf sharing APIs, +- manages the details of buffer allocation, +- decides about the actual backing storage where this allocation happens, +- takes care of any migration of scatterlist - for all (shared) users of this + buffer, + +The buffer-user +- is one of (many) sharing users of the buffer. +- doesn't need to worry about how the buffer is allocated, or where. +- needs a mechanism to get access to the scatterlist that makes up this buffer + in memory, mapped into its own address space, so it can access the same area + of memory. + +*IMPORTANT*: [see https://lkml.org/lkml/2011/12/20/211 for more details] +For this first version, A buffer shared using the dma_buf sharing API: +- *may* be exported to user space using "mmap" *ONLY* by exporter, outside of + this framework. +- may be used *ONLY* by importers that do not need CPU access to the buffer. + +The dma_buf buffer sharing API usage contains the following steps: + +1. Exporter announces that it wishes to export a buffer +2. Userspace gets the file descriptor associated with the exported buffer, and + passes it around to potential buffer-users based on use case +3. Each buffer-user 'connects' itself to the buffer +4. When needed, buffer-user requests access to the buffer from exporter +5. When finished with its use, the buffer-user notifies end-of-DMA to exporter +6. when buffer-user is done using this buffer completely, it 'disconnects' + itself from the buffer. + + +1. Exporter's announcement of buffer export + + The buffer exporter announces its wish to export a buffer. In this, it + connects its own private buffer data, provides implementation for operations + that can be performed on the exported dma_buf, and flags for the file + associated with this buffer. + + Interface: + struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops, + size_t size, int flags) + + If this succeeds, dma_buf_export allocates a dma_buf structure, and returns a + pointer to the same. It also associates an anonymous file with this buffer, + so it can be exported. On failure to allocate the dma_buf object, it returns + NULL. + +2. Userspace gets a handle to pass around to potential buffer-users + + Userspace entity requests for a file-descriptor (fd) which is a handle to the + anonymous file associated with the buffer. It can then share the fd with other + drivers and/or processes. + + Interface: + int dma_buf_fd(struct dma_buf *dmabuf) + + This API installs an fd for the anonymous file associated with this buffer; + returns either 'fd', or error. + +3. Each buffer-user 'connects' itself to the buffer + + Each buffer-user now gets a reference to the buffer, using the fd passed to + it. + + Interface: + struct dma_buf *dma_buf_get(int fd) + + This API will return a reference to the dma_buf, and increment refcount for + it. + + After this, the buffer-user needs to attach its device with the buffer, which + helps the exporter to know of device buffer constraints. + + Interface: + struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, + struct device *dev) + + This API returns reference to an attachment structure, which is then used + for scatterlist operations. It will optionally call the 'attach' dma_buf + operation, if provided by the exporter. + + The dma-buf sharing framework does the bookkeeping bits related to managing + the list of all attachments to a buffer. + +Until this stage, the buffer-exporter has the option to choose not to actually +allocate the backing storage for this buffer, but wait for the first buffer-user +to request use of buffer for allocation. + + +4. When needed, buffer-user requests access to the buffer + + Whenever a buffer-user wants to use the buffer for any DMA, it asks for + access to the buffer using dma_buf_map_attachment API. At least one attach to + the buffer must have happened before map_dma_buf can be called. + + Interface: + struct sg_table * dma_buf_map_attachment(struct dma_buf_attachment *, + enum dma_data_direction); + + This is a wrapper to dma_buf->ops->map_dma_buf operation, which hides the + "dma_buf->ops->" indirection from the users of this interface. + + In struct dma_buf_ops, map_dma_buf is defined as + struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *, + enum dma_data_direction); + + It is one of the buffer operations that must be implemented by the exporter. + It should return the sg_table containing scatterlist for this buffer, mapped + into caller's address space. + + If this is being called for the first time, the exporter can now choose to + scan through the list of attachments for this buffer, collate the requirements + of the attached devices, and choose an appropriate backing storage for the + buffer. + + Based on enum dma_data_direction, it might be possible to have multiple users + accessing at the same time (for reading, maybe), or any other kind of sharing + that the exporter might wish to make available to buffer-users. + + map_dma_buf() operation can return -EINTR if it is interrupted by a signal. + + +5. When finished, the buffer-user notifies end-of-DMA to exporter + + Once the DMA for the current buffer-user is over, it signals 'end-of-DMA' to + the exporter using the dma_buf_unmap_attachment API. + + Interface: + void dma_buf_unmap_attachment(struct dma_buf_attachment *, + struct sg_table *); + + This is a wrapper to dma_buf->ops->unmap_dma_buf() operation, which hides the + "dma_buf->ops->" indirection from the users of this interface. + + In struct dma_buf_ops, unmap_dma_buf is defined as + void (*unmap_dma_buf)(struct dma_buf_attachment *, struct sg_table *); + + unmap_dma_buf signifies the end-of-DMA for the attachment provided. Like + map_dma_buf, this API also must be implemented by the exporter. + + +6. when buffer-user is done using this buffer, it 'disconnects' itself from the + buffer. + + After the buffer-user has no more interest in using this buffer, it should + disconnect itself from the buffer: + + - it first detaches itself from the buffer. + + Interface: + void dma_buf_detach(struct dma_buf *dmabuf, + struct dma_buf_attachment *dmabuf_attach); + + This API removes the attachment from the list in dmabuf, and optionally calls + dma_buf->ops->detach(), if provided by exporter, for any housekeeping bits. + + - Then, the buffer-user returns the buffer reference to exporter. + + Interface: + void dma_buf_put(struct dma_buf *dmabuf); + + This API then reduces the refcount for this buffer. + + If, as a result of this call, the refcount becomes 0, the 'release' file + operation related to this fd is called. It calls the dmabuf->ops->release() + operation in turn, and frees the memory allocated for dmabuf when exported. + +NOTES: +- Importance of attach-detach and {map,unmap}_dma_buf operation pairs + The attach-detach calls allow the exporter to figure out backing-storage + constraints for the currently-interested devices. This allows preferential + allocation, and/or migration of pages across different types of storage + available, if possible. + + Bracketing of DMA access with {map,unmap}_dma_buf operations is essential + to allow just-in-time backing of storage, and migration mid-way through a + use-case. + +- Migration of backing storage if needed + If after + - at least one map_dma_buf has happened, + - and the backing storage has been allocated for this buffer, + another new buffer-user intends to attach itself to this buffer, it might + be allowed, if possible for the exporter. + + In case it is allowed by the exporter: + if the new buffer-user has stricter 'backing-storage constraints', and the + exporter can handle these constraints, the exporter can just stall on the + map_dma_buf until all outstanding access is completed (as signalled by + unmap_dma_buf). + Once all users have finished accessing and have unmapped this buffer, the + exporter could potentially move the buffer to the stricter backing-storage, + and then allow further {map,unmap}_dma_buf operations from any buffer-user + from the migrated backing-storage. + + If the exporter cannot fulfil the backing-storage constraints of the new + buffer-user device as requested, dma_buf_attach() would return an error to + denote non-compatibility of the new buffer-sharing request with the current + buffer. + + If the exporter chooses not to allow an attach() operation once a + map_dma_buf() API has been called, it simply returns an error. + +References: +[1] struct dma_buf_ops in include/linux/dma-buf.h +[2] All interfaces mentioned above defined in include/linux/dma-buf.h diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig index 21cf46f4524..e95c67edb2c 100644 --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -174,4 +174,15 @@ 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 + depends on EXPERIMENTAL + 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 1334d893b56..2c8272dd93c 100644 --- a/drivers/base/Makefile +++ b/drivers/base/Makefile @@ -9,6 +9,7 @@ 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 00000000000..e38ad243b4b --- /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 00000000000..f8ac076afa5 --- /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; + /* 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__ */ |