On Friday 02 Sep 2016 00:22:42 Laurent Pinchart wrote: > On Monday 29 Aug 2016 12:13:40 Sakari Ailus wrote: > > On Wed, Aug 17, 2016 at 03:20:27PM +0300, Laurent Pinchart wrote: > >> The metadata buffer type is used to transfer metadata between userspace > >> and kernelspace through a V4L2 buffers queue. It comes with a new > >> metadata capture capability and format description. > >> > >> Signed-off-by: Laurent Pinchart > >> <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > >> Tested-by: Guennadi Liakhovetski <guennadi.liakhovetski@xxxxxxxxx> > >> --- > >> Changes since v1: > >> > >> - Rebased on top of the DocBook to reST conversion > >> > >> Documentation/media/uapi/v4l/buffer.rst | 8 +++ > >> Documentation/media/uapi/v4l/dev-meta.rst | 69 +++++++++++++++++ > >> Documentation/media/uapi/v4l/devices.rst | 1 + > >> Documentation/media/uapi/v4l/vidioc-querycap.rst | 14 +++-- > >> Documentation/media/videodev2.h.rst.exceptions | 2 + > >> drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 19 +++++++ > >> drivers/media/v4l2-core/v4l2-dev.c | 16 +++--- > >> drivers/media/v4l2-core/v4l2-ioctl.c | 41 ++++++++++++++ > >> drivers/media/v4l2-core/videobuf2-v4l2.c | 3 ++ > >> include/media/v4l2-ioctl.h | 17 ++++++ > >> include/uapi/linux/videodev2.h | 14 +++++ > >> 11 files changed, 195 insertions(+), 9 deletions(-) > >> create mode 100644 Documentation/media/uapi/v4l/dev-meta.rst > > [snip] > > >> diff --git a/Documentation/media/uapi/v4l/dev-meta.rst > >> b/Documentation/media/uapi/v4l/dev-meta.rst new file mode 100644 > >> index 000000000000..252ed05b4841 > >> --- /dev/null > >> +++ b/Documentation/media/uapi/v4l/dev-meta.rst > >> @@ -0,0 +1,69 @@ > >> +.. -*- coding: utf-8; mode: rst -*- > >> + > >> +.. _metadata: > >> + > >> +****************** > >> +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. + > >> +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. > >> + > >> +.. note:: > >> + > >> + This is an :ref:`experimental` interface and may > >> + change in the future. > >> + > >> +Querying Capabilities > >> +===================== > >> + > >> +Device nodes supporting the metadata interface set the > >> ``V4L2_CAP_META_CAPTURE`` +flag in the ``device_caps`` field of the > >> +:ref:`v4l2_capability <v4l2-capability>` structure returned by the > >> +:ref:`VIDIOC_QUERYCAP` ioctl. That flag means the device can capture > >> +metadata to memory. > >> + > >> +At least one of the read/write or streaming I/O methods must be > >> supported. > >> + > >> + > >> +Data Format Negotiation > >> +======================= > >> + > >> +The metadata device uses the :ref:`format` ioctls to select the capture > >> format. +The metadata buffer content format is bound to that selected > >> format. In addition +to the basic :ref:`format` ioctls, the > >> > >> :ref:`VIDIOC_ENUM_FMT` ioctl must be +supported as well. > >> > >> + > >> +To use the :ref:`format` ioctls applications set the ``type`` of the > >> +:ref:`v4l2_format <v4l2-format>` structure to > >> ``V4L2_BUF_TYPE_META_CAPTURE`` +and use the :ref:`v4l2_meta_format > >> <v4l2-meta-format>` ``meta`` member of the +``fmt`` union as needed per > >> the desired operation. The :ref:`v4l2-meta-format` +structure contains > >> two fields, ``dataformat`` is set by applications to the V4L2 > > > > I might not specify the number of number of fields here. It has high > > chances of not getting updated when more fields are added. Up to you. > > This has been copied from dev-sdr.rst. I can drop the last sentence > completely as the parameters are described in the table below. Hans, any > opinion ? How about this ? To use the :ref:`format` ioctls applications set the ``type`` of the :ref:`v4l2_format <v4l2-format>` structure to ``V4L2_BUF_TYPE_META_CAPTURE`` and use the :ref:`v4l2_meta_format <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 :ref:`v4l2_format <v4l2-format>` structure to 0. > >> +FourCC code of the desired format, and ``buffersize`` set by drivers to > >> the > >> +maximum buffer size (in bytes) required for data transfer. > >> + > >> +.. _v4l2-meta-format: > >> +.. flat-table:: struct v4l2_meta_format > >> + :header-rows: 0 > >> + :stub-columns: 0 > >> + :widths: 1 1 2 > >> + > >> + * - __u32 > >> + - ``dataformat`` > >> + - The data format, set by the application. This is a little > >> endian > >> + :ref:`four character code <v4l2-fourcc>`. V4L2 defines metadata > >> formats > >> + in :ref:`meta-formats`. > >> + * - __u32 > >> + - ``buffersize`` > >> + - Maximum buffer size in bytes required for data. The value is > >> set by the > >> + driver. > > > > We'll need to add width and heigth as well but it could be done later on. > > Unless you have a use case you can upstream now for those fields we'll have > to add them later. > > >> + * - __u8 > >> + - ``reserved[24]`` > >> + - This array is reserved for future extensions. Drivers and > >> applications > >> + must set it to zero. > > > > struct v4l2_pix_format has grown without use of reserved fields and it's > > been around for ages. > > > > It's not directly used in an IOCTL but within an union in another struct > > so this is possible. I would consider doing the same here. Or at least > > increasing the number of reserved fields (and possibly making the type > > u32) if you feel we shouldn't go that way. > > I'm fine with dropping the reserved fields. -- Regards, Laurent Pinchart
