media: docs-rst: v4l: Document V4L2_BUF_TYPE_META_OUTPUT interface

Document the interface for metadata output, including
V4L2_BUF_TYPE_META_OUTPUT buffer type and V4L2_CAP_META_OUTPUT capability
bits.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Tested-by: Tian Shu Qiu <tian.shu.qiu@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

1 files changed, 20 insertions, 13 deletions

diff --git a/Documentation/media/uapi/v4l/dev-meta.rst b/Documentation/media/uapi/v4l/dev-meta.rst
index edccb9bd8858c..c5dbe882be654 100644
--- a/Documentation/media/uapi/v4l/dev-meta.rst
+++ b/Documentation/media/uapi/v4l/dev-meta.rst
@@ -14,21 +14,27 @@ Metadata Interface
 ******************
 
 Metadata refers to any non-image data that supplements video frames with
-additional information. This may include statistics computed over the image
-or frame capture parameters supplied by the image source. This interface is
-intended for transfer of metadata to userspace and control of that operation.
+additional information. This may include statistics computed over the image,
+frame capture parameters supplied by the image source or device specific
+parameters for specifying how the device processes images. This interface is
+intended for transfer of metadata between the userspace and the hardware and
+control of that operation.
 
-The metadata interface is implemented on video capture device nodes. The device
-can be dedicated to metadata or can implement both video and metadata capture
-as specified in its reported capabilities.
+The metadata interface is implemented on video device nodes. The device can be
+dedicated to metadata or can support both video and metadata as specified in its
+reported capabilities.
 
 Querying Capabilities
 =====================
 
-Device nodes supporting the metadata interface set the ``V4L2_CAP_META_CAPTURE``
-flag in the ``device_caps`` field of the
+Device nodes supporting the metadata capture interface set the
+``V4L2_CAP_META_CAPTURE`` flag in the ``device_caps`` field of the
 :c:type:`v4l2_capability` structure returned by the :c:func:`VIDIOC_QUERYCAP`
-ioctl. That flag means the device can capture metadata to memory.
+ioctl. That flag means the device can capture metadata to memory. Similarly,
+device nodes supporting metadata output interface set the
+``V4L2_CAP_META_OUTPUT`` flag in the ``device_caps`` field of
+:c:type:`v4l2_capability` structure. That flag means the device can read
+metadata from memory.
 
 At least one of the read/write or streaming I/O methods must be supported.
 
@@ -42,10 +48,11 @@ to the basic :ref:`format` ioctls, the :c:func:`VIDIOC_ENUM_FMT` ioctl must be
 supported as well.
 
 To use the :ref:`format` ioctls applications set the ``type`` field of the
-:c:type:`v4l2_format` structure to ``V4L2_BUF_TYPE_META_CAPTURE`` and use the
-:c:type:`v4l2_meta_format` ``meta`` member of the ``fmt`` union as needed per
-the desired operation. Both drivers and applications must set the remainder of
-the :c:type:`v4l2_format` structure to 0.
+:c:type:`v4l2_format` structure to ``V4L2_BUF_TYPE_META_CAPTURE`` or to
+``V4L2_BUF_TYPE_META_OUTPUT`` and use the :c:type:`v4l2_meta_format` ``meta``
+member of the ``fmt`` union as needed per the desired operation. Both drivers
+and applications must set the remainder of the :c:type:`v4l2_format` structure
+to 0.
 
 .. c:type:: v4l2_meta_format