Hi Sakari, 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 ? > > +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
