1 files changed, 24 insertions, 8 deletions
diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst
index f92a32d095..0c153d79cc 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.
-
-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.
+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.
+
 
 Shared DMA Buffers
 ------------------