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Diffstat (limited to 'Documentation/driver-api/dma-buf.rst')
| -rw-r--r-- | Documentation/driver-api/dma-buf.rst | 32 |
1 files changed, 24 insertions, 8 deletions
diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst index f92a32d095d9..29abf1eebf9f 100644 --- a/Documentation/driver-api/dma-buf.rst +++ b/Documentation/driver-api/dma-buf.rst @@ -5,14 +5,30 @@ 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. +As an example, it is used extensively by the DRM subsystem to exchange +buffers between processes, contexts, library APIs within the same +process, and also to exchange buffers with other subsystems such as +V4L2. + +This document describes the way in which kernel subsystems can use and +interact with the three main primitives offered by dma-buf: + + - dma-buf, representing a sg_table and exposed to userspace as a file + descriptor to allow passing between processes, subsystems, devices, + etc; + - dma-fence, providing a mechanism to signal when an asynchronous + hardware operation has completed; and + - dma-resv, which manages a set of dma-fences for a particular dma-buf + allowing implicit (kernel-ordered) synchronization of work to + preserve the illusion of coherent access + + +Userspace API principles and use +-------------------------------- + +For more details on how to design your subsystem's API for dma-buf use, please +see Documentation/userspace-api/dma-buf-alloc-exchange.rst. -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 has finished access, and (3) reservation, which manages the -shared or exclusive fence(s) associated with the buffer. Shared DMA Buffers ------------------ @@ -61,7 +77,7 @@ consider though: 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 + If llseek on dma-buf FDs isn't supported the kernel will report -ESPIPE for all cases. Userspace can use this to detect support for discovering the dma-buf size using llseek. |