doc: uapi: Add document describing dma-buf semantics

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 <daniels@collabora.com> Signed-off-by: Simon Ser <contact@emersion.fr> Reviewed-by: Simon Ser <contact@emersion.fr> Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20230803154908.105124-4-daniels@collabora.com
OpenMandrivaSoftware · Oct 30, 2023 · 051c423 · 051c423
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diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst
@@ -22,6 +22,14 @@ interact with the three main primitives offered by 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
 ------------------
 

diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
@@ -486,3 +486,10 @@ and the CRTC index is its position in this array.
 
 .. kernel-doc:: include/uapi/drm/drm_mode.h
    :internal:
+
+
+dma-buf interoperability
+========================
+
+Please see Documentation/userspace-api/dma-buf-alloc-exchange.rst for
+information on how dma-buf is integrated and exposed within DRM.