Document when should the user specify V4L2_BUF_FLAG_NO_CACHE_SYNC flag.
Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
Documentation/media/uapi/v4l/buffer.rst | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
index 9eb42bd..e1f93dd 100644
--- a/Documentation/media/uapi/v4l/buffer.rst
+++ b/Documentation/media/uapi/v4l/buffer.rst
@@ -570,6 +570,27 @@ Buffer Flags
then read by another one, in which case the flag should be set in both
:ref:`VIDIOC_QBUF` and :ref:`VIDIOC_DQBUF` ioctls. This flag has no
effect on some devices / architectures.
+
+ More specifically, this flag causes cache synchronisation to
+ be skipped for OUTPUT buffers when the buffer is queued. The
+ flag can be used if the buffer has been previously written to
+ by hardware but has not been written to by the CPU.
+
+ Additionally, if this flag is specified for a CAPTURE buffer
+ when it is queued, cache synchronisation is skipped. This
+ signals that the application can guarantee that it has not
+ written to the buffer memory since it was last dequeued from
+ the device.
+
+ Specifying this flag for a CAPTURE buffer when
+ dequeueing a buffer will skip cache maintenance for the buffer
+ memory. An application may not access the buffer memory in
+ that case but it may well be passed onwards to another device
+ in the system.
+
+ Specifying this flag has no effect when dequeuing an OUTPUT
+ buffer.
+
* .. _`V4L2-BUF-FLAG-LAST`:
- ``V4L2_BUF_FLAG_LAST``
--
2.7.4
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