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doc: dma-buf: Rewrite intro section a little
Make it a little bit more clear what's going on and fix some formatting.
Signed-off-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Simon Ser <contact@emersion.fr>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20230803154908.105124-3-daniels@collabora.com
authored by
Daniel Stone
and committed by
Simon Ser
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d7a407bc
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Documentation/driver-api/dma-buf.rst
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Documentation/driver-api/dma-buf.rst
···
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hardware (DMA) access across multiple device drivers and subsystems, and
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for synchronizing asynchronous hardware access.
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This is used, for example, by drm "prime" multi-GPU support, but is of
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course not limited to GPU use cases.
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As an example, it is used extensively by the DRM subsystem to exchange
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buffers between processes, contexts, library APIs within the same
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process, and also to exchange buffers with other subsystems such as
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V4L2.
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The three main components of this are: (1) dma-buf, representing a
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sg_table and exposed to userspace as a file descriptor to allow passing
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between devices, (2) fence, which provides a mechanism to signal when
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one device has finished access, and (3) reservation, which manages the
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shared or exclusive fence(s) associated with the buffer.
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This document describes the way in which kernel subsystems can use and
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interact with the three main primitives offered by dma-buf:
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- dma-buf, representing a sg_table and exposed to userspace as a file
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descriptor to allow passing between processes, subsystems, devices,
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etc;
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- dma-fence, providing a mechanism to signal when an asynchronous
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hardware operation has completed; and
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- dma-resv, which manages a set of dma-fences for a particular dma-buf
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allowing implicit (kernel-ordered) synchronization of work to
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preserve the illusion of coherent access
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Shared DMA Buffers
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------------------