dma-buf: Extract dma-buf.rst

Just prep work to polish and consolidate all the dma-buf related
documenation.

Unfortunately I didn't discover a way to both integrate this new file
into the overall toc while keeping it at the current place. Work
around that by moving it into the overall driver-api/index.rst.

Cc: linux-doc@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-api/dma-buf.rst

+Buffer Sharing and Synchronization
+==================================
+
+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 as finished access, and (3) reservation, which manages the
+shared or exclusive fence(s) associated with the buffer.
+
+Shared DMA Buffers
+------------------
+
+.. kernel-doc:: drivers/dma-buf/dma-buf.c
+   :export:
+
+.. kernel-doc:: include/linux/dma-buf.h
+   :internal:
+
+Reservation Objects
+-------------------
+
+.. kernel-doc:: drivers/dma-buf/reservation.c
+   :doc: Reservation Object Overview
+
+.. kernel-doc:: drivers/dma-buf/reservation.c
+   :export:
+
+.. kernel-doc:: include/linux/reservation.h
+   :internal:
+
+DMA Fences
+----------
+
+.. kernel-doc:: drivers/dma-buf/dma-fence.c
+   :export:
+
+.. kernel-doc:: include/linux/dma-fence.h
+   :internal:
+
+Seqno Hardware Fences
+~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/seqno-fence.c
+   :export:
+
+.. kernel-doc:: include/linux/seqno-fence.h
+   :internal:
+
+DMA Fence Array
+~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/dma-fence-array.c
+   :export:
+
+.. kernel-doc:: include/linux/dma-fence-array.h
+   :internal:
+
+DMA Fence uABI/Sync File
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/dma-buf/sync_file.c
+   :export:
+
+.. kernel-doc:: include/linux/sync_file.h
+   :internal:
+

Documentation/driver-api/index.rst

@@ -16,6 +16,7 @@ available subsections can be seen below.
 
    basics
    infrastructure
+   dma-buf
    device_link
    message-based
    sound

Documentation/driver-api/infrastructure.rst

@@ -46,76 +46,6 @@ Device Drivers Base
 .. kernel-doc:: drivers/base/bus.c
    :export:
 
-Buffer Sharing and Synchronization
-----------------------------------
-
-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 as finished access, and (3) reservation, which manages the
-shared or exclusive fence(s) associated with the buffer.
-
-dma-buf
-~~~~~~~
-
-.. kernel-doc:: drivers/dma-buf/dma-buf.c
-   :export:
-
-.. kernel-doc:: include/linux/dma-buf.h
-   :internal:
-
-reservation
-~~~~~~~~~~~
-
-.. kernel-doc:: drivers/dma-buf/reservation.c
-   :doc: Reservation Object Overview
-
-.. kernel-doc:: drivers/dma-buf/reservation.c
-   :export:
-
-.. kernel-doc:: include/linux/reservation.h
-   :internal:
-
-fence
-~~~~~
-
-.. kernel-doc:: drivers/dma-buf/dma-fence.c
-   :export:
-
-.. kernel-doc:: include/linux/dma-fence.h
-   :internal:
-
-.. kernel-doc:: drivers/dma-buf/seqno-fence.c
-   :export:
-
-.. kernel-doc:: include/linux/seqno-fence.h
-   :internal:
-
-.. kernel-doc:: drivers/dma-buf/dma-fence-array.c
-   :export:
-
-.. kernel-doc:: include/linux/dma-fence-array.h
-   :internal:
-
-.. kernel-doc:: drivers/dma-buf/reservation.c
-   :export:
-
-.. kernel-doc:: include/linux/reservation.h
-   :internal:
-
-.. kernel-doc:: drivers/dma-buf/sync_file.c
-   :export:
-
-.. kernel-doc:: include/linux/sync_file.h
-   :internal:
-
 Device Drivers DMA Management
 -----------------------------