Commit e941759c74a44d6ac2eed21bb0a38b21fe4559e2 ("fence: dma-buf cross-device synchronization (v18)") had a spurious kerneldoc section header that caused Sphinx to complain. Fix it.

Fixes: e941759c74a4 ("fence: dma-buf cross-device synchronization (v18)")

Signed-off-by: Sumit Semwal sumit.semwal@linaro.org --- include/linux/fence.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fence.h b/include/linux/fence.h index 5aa95eb886f7..5de89dab0013 100644 --- a/include/linux/fence.h +++ b/include/linux/fence.h @@ -60,7 +60,7 @@ struct fence_cb; * implementer of the fence for its own purposes. Can be used in different * ways by different fence implementers, so do not rely on this. * - * *) Since atomic bitops are used, this is not guaranteed to be the case. + * Since atomic bitops are used, this is not guaranteed to be the case. * Particularly, if the bit was set, but fence_signal was called right * before this bit was set, it would have been able to set the * FENCE_FLAG_SIGNALED_BIT, before enable_signaling was called.

Branch out dma-buf related documentation into its own rst file to allow adding it to the sphinx documentation generated.

While at it, move dma-buf-sharing.txt into rst as the dma-buf guide too.

Signed-off-by: Sumit Semwal sumit.semwal@linaro.org --- Documentation/DocBook/device-drivers.tmpl | 37 --- Documentation/dma-buf/guide.rst | 503 ++++++++++++++++++++++++++++++ Documentation/dma-buf/intro.rst | 76 +++++ MAINTAINERS | 2 +- 4 files changed, 580 insertions(+), 38 deletions(-) create mode 100644 Documentation/dma-buf/guide.rst create mode 100644 Documentation/dma-buf/intro.rst

diff --git a/Documentation/DocBook/device-drivers.tmpl b/Documentation/DocBook/device-drivers.tmpl index 99cdc05bbb7a..a93fbffa9742 100644 --- a/Documentation/DocBook/device-drivers.tmpl +++ b/Documentation/DocBook/device-drivers.tmpl @@ -128,43 +128,6 @@ X!Edrivers/base/interface.c !Edrivers/base/platform.c !Edrivers/base/bus.c </sect1> - <sect1> - <title>Buffer Sharing and Synchronization</title> - <para> - The dma-buf subsystem provides the framework for sharing buffers - for hardware (DMA) access across multiple device drivers and - subsystems, and for synchronizing asynchronous hardware access. - </para> - <para> - This is used, for example, by drm "prime" multi-GPU support, but - is of course not limited to GPU use cases. - </para> - <para> - The three main components of this are: (1) dma-buf, representing - a sg_table and exposed to userspace as a file descriptor to allow - passing between devices, (2) fence, which provides a mechanism - to signal when one device as finished access, and (3) reservation, - which manages the shared or exclusive fence(s) associated with - the buffer. - </para> - <sect2><title>dma-buf</title> -!Edrivers/dma-buf/dma-buf.c -!Iinclude/linux/dma-buf.h - </sect2> - <sect2><title>reservation</title> -!Pdrivers/dma-buf/reservation.c Reservation Object Overview -!Edrivers/dma-buf/reservation.c -!Iinclude/linux/reservation.h - </sect2> - <sect2><title>fence</title> -!Edrivers/dma-buf/fence.c -!Iinclude/linux/fence.h -!Edrivers/dma-buf/seqno-fence.c -!Iinclude/linux/seqno-fence.h -!Edrivers/dma-buf/sync_file.c -!Iinclude/linux/sync_file.h - </sect2> - </sect1> <sect1><title>Device Drivers DMA Management</title> !Edrivers/base/dma-coherent.c !Edrivers/base/dma-mapping.c diff --git a/Documentation/dma-buf/guide.rst b/Documentation/dma-buf/guide.rst new file mode 100644 index 000000000000..fd3534fdccb3 --- /dev/null +++ b/Documentation/dma-buf/guide.rst @@ -0,0 +1,503 @@ + +.. _dma-buf-guide: + +============================ +DMA Buffer Sharing API Guide +============================ + +Sumit Semwal - sumit.semwal@linaro.org, sumits@kernel.org + +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 for the buffer via + :c:type:`struct dma_buf_ops <dma_buf_ops>` +* 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. + +dma-buf operations for device dma only +====================================== + +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 :c:type:`dma_buf`, and flags for the file + associated with this buffer. All these fields are filled in struct + :c:type:`dma_buf_export_info`, defined via the DEFINE_DMA_BUF_EXPORT_INFO macro. + + Interface: + :c:type:`DEFINE_DMA_BUF_EXPORT_INFO(exp_info) <DEFINE_DMA_BUF_EXPORT_INFO>` + + :c:func:`struct dma_buf *dma_buf_export(struct dma_buf_export_info *exp_info)<dma_buf_export>` + + 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. + + 'exp_name' in struct dma_buf_export_info is the name of exporter - to + facilitate information while debugging. It is set to KBUILD_MODNAME by + default, so exporters don't have to provide a specific name, if they don't + wish to. + + DEFINE_DMA_BUF_EXPORT_INFO macro defines the struct dma_buf_export_info, + zeroes it out and pre-populates exp_name in it. + +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: + :c:func:`int dma_buf_fd(struct dma_buf *dmabuf, int flags) <dma_buf_fd>` + + 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: + :c:func:`struct dma_buf *dma_buf_get(int fd) <dma_buf_get>` + + 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: + :c:func:`struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf, struct device *dev) <dma_buf_attach>` + + 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. + +.. note:: 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: + :c:func:`struct sg_table * dma_buf_map_attachment(struct dma_buf_attachment *, enum dma_data_direction) <dma_buf_map_attachment>` + + 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 :c:type:`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 :c:type:`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: + :c:func:`void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *) <dma_buf_unmap_attachment>` + + 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 *, enum dma_data_direction)`` + + 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: + :c:func:`void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *dmabuf_attach) <dma_buf_detach>` + + 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: + :c:func:`void dma_buf_put(struct dma_buf *dmabuf) <dma_buf_put>` + + 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 fulfill 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. + +Kernel cpu access to a dma-buf buffer object +============================================ + +The motivation to allow cpu access from the kernel to a dma-buf object from the +importers side are: + +* fallback operations, e.g. if the devices is connected to a usb bus and the + kernel needs to shuffle the data around first before sending it away. +* full transparency for existing users on the importer side, i.e. userspace + should not notice the difference between a normal object from that subsystem + and an imported one backed by a dma-buf. This is really important for drm + opengl drivers that expect to still use all the existing upload/download + paths. + +Access to a dma_buf from the kernel context involves three steps: + +1. Prepare access, which invalidate any necessary caches and make the object + available for cpu access. +2. Access the object page-by-page with the dma_buf map apis +3. Finish access, which will flush any necessary cpu caches and free reserved + resources. + +1. Prepare access +----------------- + + Before an importer can access a dma_buf object with the cpu from the kernel + context, it needs to notify the exporter of the access that is about to + happen. + + Interface: + :c:func:`int dma_buf_begin_cpu_access(struct dma_buf *dmabuf, enum dma_data_direction direction) <dma_buf_begin_cpu_access>` + + This allows the exporter to ensure that the memory is actually available for + cpu access - the exporter might need to allocate or swap-in and pin the + backing storage. The exporter also needs to ensure that cpu access is + coherent for the access direction. The direction can be used by the exporter + to optimize the cache flushing, i.e. access with a different direction (read + instead of write) might return stale or even bogus data (e.g. when the + exporter needs to copy the data to temporary storage). + + This step might fail, e.g. in oom conditions. + +2. Accessing the buffer +----------------------- + + To support dma_buf objects residing in highmem cpu access is page-based using + an api similar to kmap. Accessing a dma_buf is done in aligned chunks of + PAGE_SIZE size. Before accessing a chunk it needs to be mapped, which returns + a pointer in kernel virtual address space. Afterwards the chunk needs to be + unmapped again. There is no limit on how often a given chunk can be mapped + and unmapped, i.e. the importer does not need to call begin_cpu_access again + before mapping the same chunk again. + + Interfaces: + :c:func:`void *dma_buf_kmap(struct dma_buf *, unsigned long) <dma_buf_kmap>` + + :c:func:`void dma_buf_kunmap(struct dma_buf *, unsigned long, void *) <dma_buf_kunmap>` + + There are also atomic variants of these interfaces. Like for kmap they + facilitate non-blocking fast-paths. Neither the importer nor the exporter (in + the callback) is allowed to block when using these. + + Interfaces: + :c:func:`void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long) <dma_buf_kmap_atomic>` + + :c:func:`void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *) <dma_buf_kunmap_atomic>` + + For importers all the restrictions of using kmap apply, like the limited + supply of kmap_atomic slots. Hence an importer shall only hold onto at most 2 + atomic dma_buf kmaps at the same time (in any given process context). + + dma_buf kmap calls outside of the range specified in begin_cpu_access are + undefined. If the range is not PAGE_SIZE aligned, kmap needs to succeed on + the partial chunks at the beginning and end but may return stale or bogus + data outside of the range (in these partial chunks). + + Note that these calls need to always succeed. The exporter needs to complete + any preparations that might fail in begin_cpu_access. + + For some cases the overhead of kmap can be too high, a vmap interface + is introduced. This interface should be used very carefully, as vmalloc + space is a limited resources on many architectures. + + Interfaces: + :c:func:`void *dma_buf_vmap(struct dma_buf *dmabuf) <dma_buf_vmap>` + + :c:func:`void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr) <dma_buf_vunmap>` + + The vmap call can fail if there is no vmap support in the exporter, or if it + runs out of vmalloc space. Fallback to kmap should be implemented. Note that + the dma-buf layer keeps a reference count for all vmap access and calls down + into the exporter's vmap function only when no vmapping exists, and only + unmaps it once. Protection against concurrent vmap/vunmap calls is provided + by taking the dma_buf->lock mutex. + +3. Finish access +---------------- + + When the importer is done accessing the CPU, it needs to announce this to + the exporter (to facilitate cache flushing and unpinning of any pinned + resources). The result of any dma_buf kmap calls after end_cpu_access is + undefined. + + Interface: + :c:func:`void dma_buf_end_cpu_access(struct dma_buf *dma_buf, enum dma_data_direction dir) <dma_buf_end_cpu_access>` + + +Direct Userspace Access/mmap Support +==================================== + +Being able to mmap an export dma-buf buffer object has 2 main use-cases: +* CPU fallback processing in a pipeline and +* supporting existing mmap interfaces in importers. + +1. CPU fallback processing in a pipeline +---------------------------------------- + + In many processing pipelines it is sometimes required that the cpu can access + the data in a dma-buf (e.g. for thumbnail creation, snapshots, ...). To avoid + the need to handle this specially in userspace frameworks for buffer sharing + it's ideal if the dma_buf fd itself can be used to access the backing storage + from userspace using mmap. + + Furthermore Android's ION framework already supports this (and is otherwise + rather similar to dma-buf from a userspace consumer side with using fds as + handles, too). So it's beneficial to support this in a similar fashion on + dma-buf to have a good transition path for existing Android userspace. + + No special interfaces, userspace simply calls mmap on the dma-buf fd, making + sure that the cache synchronization ioctl (DMA_BUF_IOCTL_SYNC) is *always* + used when the access happens. Note that DMA_BUF_IOCTL_SYNC can fail with + -EAGAIN or -EINTR, in which case it must be restarted. + + Some systems might need some sort of cache coherency management e.g. when + CPU and GPU domains are being accessed through dma-buf at the same time. To + circumvent this problem there are begin/end coherency markers, that forward + directly to existing dma-buf device drivers vfunc hooks. Userspace can make + use of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The sequence + would be used like following: + + * mmap dma-buf fd + * for each drawing/upload cycle in CPU + + 1. SYNC_START ioctl, + 2. read/write to mmap area + 3. SYNC_END ioctl. + + This can be repeated as often as you want (with the new data being + consumed by the GPU or say scanout device) + * munmap once you don't need the buffer any more + + For correctness and optimal performance, it is always required to use + SYNC_START and SYNC_END before and after, respectively, when accessing the + mapped address. Userspace cannot rely on coherent access, even when there + are systems where it just works without calling these ioctls. + +2. Supporting existing mmap interfaces in importers +--------------------------------------------------- + + Similar to the motivation for kernel cpu access it is again important that + the userspace code of a given importing subsystem can use the same interfaces + with a imported dma-buf buffer object as with a native buffer object. This is + especially important for drm where the userspace part of contemporary OpenGL, + X, and other drivers is huge, and reworking them to use a different way to + mmap a buffer rather invasive. + + The assumption in the current dma-buf interfaces is that redirecting the + initial mmap is all that's needed. A survey of some of the existing + subsystems shows that no driver seems to do any nefarious thing like syncing + up with outstanding asynchronous processing on the device or allocating + special resources at fault time. So hopefully this is good enough, since + adding interfaces to intercept pagefaults and allow pte shootdowns would + increase the complexity quite a bit. + + Interface: + :c:func:`int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *, unsigned long) <dma_buf_mmap>` + + If the importing subsystem simply provides a special-purpose mmap call to set + up a mapping in userspace, calling do_mmap with dma_buf->file will equally + achieve that for a dma-buf object. + +3. Implementation notes for exporters +------------------------------------- + + Because dma-buf buffers have invariant size over their lifetime, the dma-buf + core checks whether a vma is too large and rejects such mappings. The + exporter hence does not need to duplicate this check. + + Because existing importing subsystems might presume coherent mappings for + userspace, the exporter needs to set up a coherent mapping. If that's not + possible, it needs to fake coherency by manually shooting down ptes when + leaving the cpu domain and flushing caches at fault time. Note that all the + dma_buf files share the same anon inode, hence the exporter needs to replace + the dma_buf file stored in vma->vm_file with it's own if pte shootdown is + required. This is because the kernel uses the underlying inode's address_space + for vma tracking (and hence pte tracking at shootdown time with + unmap_mapping_range). + + If the above shootdown dance turns out to be too expensive in certain + scenarios, we can extend dma-buf with a more explicit cache tracking scheme + for userspace mappings. But the current assumption is that using mmap is + always a slower path, so some inefficiencies should be acceptable. + + Exporters that shoot down mappings (for any reasons) shall not do any + synchronization at fault time with outstanding device operations. + Synchronization is an orthogonal issue to sharing the backing storage of a + buffer and hence should not be handled by dma-buf itself. This is explicitly + mentioned here because many people seem to want something like this, but if + different exporters handle this differently, buffer sharing can fail in + interesting ways depending upong the exporter (if userspace starts depending + upon this implicit synchronization). + +Other Interfaces Exposed to Userspace on the dma-buf FD +------------------------------------------------------- + +* Since kernel 3.12 the dma-buf FD supports the llseek system call, but only + with offset=0 and whence=SEEK_END|SEEK_SET. SEEK_SET is supported to allow + the usual size discover pattern size = SEEK_END(0); SEEK_SET(0). Every other + llseek operation will report -EINVAL. + + If llseek on dma-buf FDs isn't support the kernel will report -ESPIPE for all + cases. Userspace can use this to detect support for discovering the dma-buf + size using llseek. + +Miscellaneous notes +------------------- + +* Any exporters or users of the dma-buf buffer sharing framework must have + a 'select DMA_SHARED_BUFFER' in their respective Kconfigs. + +* In order to avoid fd leaks on exec, the FD_CLOEXEC flag must be set + on the file descriptor. This is not just a resource leak, but a + potential security hole. It could give the newly exec'd application + access to buffers, via the leaked fd, to which it should otherwise + not be permitted access. + + The problem with doing this via a separate fcntl() call, versus doing it + atomically when the fd is created, is that this is inherently racy in a + multi-threaded app (See `here https://lwn.net/Articles/236486/`_). The issue + is made worse when it is library code opening/creating the file descriptor, + as the application may not even be aware of the fd's. + + To avoid this problem, userspace must have a way to request O_CLOEXEC + flag be set when the dma-buf fd is created. So any API provided by + the exporting driver to create a dmabuf fd must provide a way to let + userspace control setting of O_CLOEXEC flag passed in to dma_buf_fd(). + +- If an exporter needs to manually flush caches and hence needs to fake + coherency for mmap support, it needs to be able to zap all the ptes pointing + at the backing storage. Now linux mm needs a struct address_space associated + with the struct file stored in vma->vm_file to do that with the function + unmap_mapping_range. But the dma_buf framework only backs every dma_buf fd + with the anon_file struct file, i.e. all dma_bufs share the same file. + + Hence exporters need to setup their own file (and address_space) association + by setting vma->vm_file and adjusting vma->vm_pgoff in the dma_buf mmap + callback. In the specific case of a gem driver the exporter could use the + shmem file already provided by gem (and set vm_pgoff = 0). Exporters can then + zap ptes by unmapping the corresponding range of the struct address_space + associated with their own file. + diff --git a/Documentation/dma-buf/intro.rst b/Documentation/dma-buf/intro.rst new file mode 100644 index 000000000000..36359bbc9865 --- /dev/null +++ b/Documentation/dma-buf/intro.rst @@ -0,0 +1,76 @@ +================================== +Buffer Sharing and Synchronization +================================== + + +Introduction +------------ + +The dma-buf subsystem provides the framework for sharing buffers for +hardware (DMA) access across multiple device drivers and subsystems, and +for synchronizing asynchronous hardware access. + +This is used, for example, by drm "prime" multi-GPU support, but is of +course not limited to GPU use cases. + +The three main components of this are: + +* dma-buf_: represents an sg_table, and is exposed to userspace as a file + descriptor to allow passing between devices, + +* fence_: which provides a mechanism to signal when one device has finished + access, and + +* reservation_: manages the shared or exclusive fence(s) associated with the + buffer. + +Please refer to :ref:`DMA buffer sharing guide <dma-buf-guide>` for more details. + +.. _dma-buf: + +dma-buf +~~~~~~~ + +.. kernel-doc:: drivers/dma-buf/dma-buf.c + :export: + +.. kernel-doc:: include/linux/dma-buf.h + :internal: + +.. _fence: + +fence +~~~~~ + +.. kernel-doc:: drivers/dma-buf/fence.c + :export: + +.. kernel-doc:: include/linux/fence.h + :internal: + +.. kernel-doc:: drivers/dma-buf/seqno-fence.c + :export: + +.. kernel-doc:: include/linux/seqno-fence.h + :internal: + +.. kernel-doc:: drivers/dma-buf/sync_file.c + :export: + +.. kernel-doc:: include/linux/sync_file.h + :internal: + +.. _reservation: + +reservation +~~~~~~~~~~~ + +.. kernel-doc:: drivers/dma-buf/reservation.c + :doc: Reservation Object Overview + +.. kernel-doc:: drivers/dma-buf/reservation.c + :export: + +.. kernel-doc:: include/linux/reservation.h + :internal: + diff --git a/MAINTAINERS b/MAINTAINERS index c92defa5be2c..d58b5c4068b6 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -3816,7 +3816,7 @@ F: drivers/dma-buf/ F: include/linux/dma-buf* F: include/linux/reservation.h F: include/linux/*fence.h -F: Documentation/dma-buf-sharing.txt +F: Documentation/dma-buf/ T: git git://git.linaro.org/people/sumitsemwal/linux-dma-buf.git

DMA GENERIC OFFLOAD ENGINE SUBSYSTEM

Include dma-buf sphinx documentation into top level index.

Signed-off-by: Sumit Semwal sumit.semwal@linaro.org --- Documentation/index.rst | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/Documentation/index.rst b/Documentation/index.rst index 43c722f15292..2fe8e82d7d8c 100644 --- a/Documentation/index.rst +++ b/Documentation/index.rst @@ -14,6 +14,8 @@ Contents: :maxdepth: 2

kernel-documentation + dma-buf/intro + dma-buf/guide media/media_uapi media/media_kapi media/dvb-drivers/index