Document when should the user specify V4L2_BUF_FLAG_NO_CACHE_SYNC flag.
Signed-off-by: Sakari Ailus sakari.ailus@linux.intel.com --- 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``