Add document to describe the detials of v4l2 buffer sharing.

This document includes the steps of using DMABUF buffer sharing between
v4l2 and Beignet. Also steps to run corresponding example.

Signed-off-by: Chuanbo Weng <chuanbo.weng@intel.com>
Reviewed-by: Yuan, Feng <feng.yuan@intel.com>

2 files changed, 65 insertions, 0 deletions

diff --git a/docs/Beignet.mdwn b/docs/Beignet.mdwn
index c0650bba..2509ece6 100644
--- a/docs/Beignet.mdwn
+++ b/docs/Beignet.mdwn
@@ -305,6 +305,7 @@ Documents for OpenCL application developers
 - [[Work with old system without c++11|Beignet/howto/oldgcc-howto]]
 - [[Kernel Optimization Guide|Beignet/optimization-guide]]
 - [[Libva Buffer Sharing|Beignet/howto/libva-buffer-sharing-howto]]
+- [[V4l2 Buffer Sharing|Beignet/howto/v4l2-buffer-sharing-howto]]
 
 The wiki URL is as below:
 [http://www.freedesktop.org/wiki/Software/Beignet/](http://www.freedesktop.org/wiki/Software/Beignet/)
diff --git a/docs/howto/v4l2-buffer-sharing-howto.mdwn b/docs/howto/v4l2-buffer-sharing-howto.mdwn
new file mode 100644
index 00000000..68d37aa1
--- /dev/null
+++ b/docs/howto/v4l2-buffer-sharing-howto.mdwn
@@ -0,0 +1,64 @@
+V4l2 Buffer Sharing HowTo
+=========================
+
+Beignet has extension clGetMemObjectFdIntel to share gpu buffer object with v4l2. So users
+can utilize OpenCL to do processing on input/ouput buffers of v4l2 device without buffer copy.
+
+Prerequisite
+------------
+
+Linux kernel supports DMABUF buffer sharing for v4l2 from version 3.8. DMABUF buffer
+sharing runs well for V4L2_PIX_FMT_MJPEG format on this version, but there is a bug
+for V4L2_PIX_FMT_YUYV format. Linux kernel 3.19.0-rc1 fix this bug, so please use kernel
+version 3.19.0-rc1 at least if you want to utilize this feature for V4L2_PIX_FMT_YUYV
+format.
+
+Steps
+-----
+
+The below official v4l2 document describes the details of sharing DMA buffers between
+v4l devices and other devices using v4l2 as a DMABUF importer:
+[http://linuxtv.org/downloads/v4l-dvb-apis/dmabuf.html](http://linuxtv.org/downloads/v4l-dvb-apis/dmabuf.html)
+Beignet has added extension clGetMemObjectFdIntel to support this mechanism. Please follow
+the steps as below to utilize DMABUF buffer sharing between v4l devices and Beignet:
+
+- Get the address of this extension by the function:
+  clGetExtensionFunctionAddress("clGetMemObjectFdIntel")
+
+- Create a number of cl buffer objects, invoke clGetMemObjectFdIntel to get these buffer
+  objects' file descriptors.
+
+- Initiating streaming I/O with DMABUF buffer sharing by calling the VIDIOC_REQBUFS v4l2 ioctl.
+
+- Enqueue these buffers by calling the VIDIOC_QBUF, dequeue a buffer by calling VIDIOC_DQBUF,
+  use OpenCL to do processing on this buffer and re-enqueue...
+
+- Close file descriptors of these buffers by close if your program doesn't need DMABUF buffer
+  sharing anymore.
+
+Sample code
+-----------
+
+We have developed an example showing how to share DMA buffers between webcam and Beignet in
+examples/v4l2_buffer_sharing directory. The webcam directly captures V4L2_PIX_FMT_YUYV frames
+into cl buffer objects by the way of DMABUF buffer sharing, then frames are got mirror effect
+by OpenCL kernel, and finally show on screen by libva.
+
+Steps to build and run this example:
+
+- Update your linux kernel to at least 3.19.0-rc1.
+
+- Make sure there is a webcam connected to your pc.
+
+- Add option -DBUILD_EXAMPLES=ON to enable building examples when running cmake, such as:
+  `> mkdir build`
+  `> cd build`
+  `> cmake -DBUILD_EXAMPLES=ON ../`
+
+- Build source code:
+  `> make`
+
+- Run:
+  `> cd examples`
+  `> . ../utests/setenv.sh`
+  `> ./example-v4l2_buffer_sharing`