kernel/linux.git/Documentation/driver-api/dma-buf.rst, branch linux-7.1.y

dma-buf: Remove DMA-BUF sysfs stats

2026-01-19T13:40:01+00:00

Commit bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-BUF stats in sysfs") added dmabuf statistics to sysfs in 2021 under CONFIG_DMABUF_SYSFS_STATS. After being used in production, performance problems were discovered leading to its deprecation in 2022 in commit e0a9f1fe206a ("dma-buf: deprecate DMABUF_SYSFS_STATS"). Some of the problems with this interface were discussed in my LPC 2025 talk. [1][2] Android was probably the last user of the interface, which has since been migrated to use the dmabuf BPF iterator [3] to obtain the same information more cheaply. As promised in that series, now that the longterm stable 6.18 kernel has been released let's remove the sysfs dmabuf statistics from the kernel. [1] https://www.youtube.com/watch?v=D83qygudq9c [2] https://lpc.events/event/19/contributions/2118/ [3] https://lore.kernel.org/all/20250522230429.941193-1-tjmercier@google.com/ Signed-off-by: T.J. Mercier Reviewed-by: Christian König Signed-off-by: Sumit Semwal Link: https://patch.msgid.link/20260116190517.3268458-1-tjmercier@google.com

doc: dma-buf: fix grammar typo

2024-04-18T14:20:48+00:00

Use 'supported' instead of 'support'. 'support' makes no sense in this context. Signed-off-by: Baruch Siach Link: https://patchwork.freedesktop.org/patch/msgid/505484b83fedebce3c65b10b076b34df075074b6.1713329988.git.baruch@tkos.co.il Signed-off-by: Christian König

doc: uapi: Add document describing dma-buf semantics

2023-08-21T16:20:05+00:00

Since there's a lot of confusion around this, document both the rules and the best practices around negotiating, allocating, importing, and using buffers when crossing context/process/device/subsystem boundaries. This ties up all of dma-buf, formats and modifiers, and their usage. Signed-off-by: Daniel Stone Signed-off-by: Simon Ser Reviewed-by: Simon Ser Reviewed-by: Sui Jingfeng Acked-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20230803154908.105124-4-daniels@collabora.com

doc: dma-buf: Rewrite intro section a little

2023-08-21T15:10:33+00:00

Make it a little bit more clear what's going on and fix some formatting. Signed-off-by: Daniel Stone Signed-off-by: Simon Ser Reviewed-by: Simon Ser Acked-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20230803154908.105124-3-daniels@collabora.com

dma-buf/sync_file: Surface sync-file uABI

2023-03-28T20:39:02+00:00

We had all of the internal driver APIs, but not the all important userspace uABI, in the dma-buf doc. Fix that. And re-arrange the comments slightly as otherwise the comments for the ioctl nr defines would not show up. v2: Fix docs build warning coming from newly including the uabi header in the docs build Signed-off-by: Rob Clark Acked-by: Pekka Paalanen

dma-buf/dma-fence: Add deadline awareness

2023-03-25T17:55:07+00:00

Add a way to hint to the fence signaler of an upcoming deadline, such as vblank, which the fence waiter would prefer not to miss. This is to aid the fence signaler in making power management decisions, like boosting frequency as the deadline approaches and awareness of missing deadlines so that can be factored in to the frequency scaling. v2: Drop dma_fence::deadline and related logic to filter duplicate deadlines, to avoid increasing dma_fence size. The fence-context implementation will need similar logic to track deadlines of all the fences on the same timeline. [ckoenig] v3: Clarify locking wrt. set_deadline callback v4: Clarify in docs comment that this is a hint v5: Drop DMA_FENCE_FLAG_HAS_DEADLINE_BIT. v6: More docs v7: Fix typo, clarify past deadlines Signed-off-by: Rob Clark Reviewed-by: Christian König Acked-by: Pekka Paalanen Reviewed-by: Bagas Sanjaya

Documentation: driver-api: correct spelling

2023-02-02T18:05:16+00:00

Correct spelling problems for Documentation/driver-api/ as reported by codespell. Signed-off-by: Randy Dunlap Cc: Mauro Carvalho Chehab Cc: linux-media@vger.kernel.org Cc: Vishal Verma Cc: Dave Jiang Cc: nvdimm@lists.linux.dev Cc: Vinod Koul Cc: dmaengine@vger.kernel.org Cc: linux-raid@vger.kernel.org Cc: linux-usb@vger.kernel.org Acked-by: Dan Williams Acked-by: Song Liu Acked-by: Greg Kroah-Hartman Link: https://lore.kernel.org/r/20230129231053.20863-3-rdunlap@infradead.org Signed-off-by: Jonathan Corbet

dma-buf: Add "dma-buf" to title of documentation

2023-01-31T20:56:05+00:00

To make it easier to find the dma-buf documentation when looking through tables-of-contents etc., put the name "dma-buf" in the title. Signed-off-by: Jonathan Neuschäfer Link: https://lore.kernel.org/r/20230129115917.1229529-1-j.neuschaefer@gmx.net Signed-off-by: Jonathan Corbet

dma-buf: Document dynamic locking convention

2022-10-17T22:21:53+00:00

Add documentation for the dynamic locking convention. The documentation tells dma-buf API users when they should take the reservation lock and when not. Acked-by: Sumit Semwal Reviewed-by: Christian König Signed-off-by: Dmitry Osipenko Link: https://patchwork.freedesktop.org/patch/msgid/20221017172229.42269-20-dmitry.osipenko@collabora.com

dma-buf: add dma_fence_unwrap v2

2022-03-25T13:18:28+00:00

Add a general purpose helper to deep dive into dma_fence_chain/dma_fence_array structures and iterate over all the fences in them. This is useful when we need to flatten out all fences in those structures. v2: some selftests cleanup, improved function naming and documentation Signed-off-by: Christian König Reviewed-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20220311110244.1245-1-christian.koenig@amd.com