[media] v4l: Add subdev selections documentation
Add documentation for V4L2 subdev selection API. This changes also experimental V4L2 subdev API so that scaling now works through selection API only. Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi> Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Sakari Ailus
Mauro Carvalho Chehab
parent
59ef29cc86
commit
955f645aea
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@ -70,6 +70,8 @@ IOCTLS = \
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VIDIOC_SUBDEV_ENUM_MBUS_CODE \
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VIDIOC_SUBDEV_ENUM_FRAME_SIZE \
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VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL \
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VIDIOC_SUBDEV_G_SELECTION \
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VIDIOC_SUBDEV_S_SELECTION \
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TYPES = \
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$(shell perl -ne 'print "$$1 " if /^typedef\s+[^\s]+\s+([^\s]+)\;/' $(srctree)/include/linux/videodev2.h) \
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@ -193,7 +195,7 @@ DVB_DOCUMENTED = \
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#
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install_media_images = \
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$(Q)cp $(OBJIMGFILES) $(MEDIA_OBJ_DIR)/media_api
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$(Q)cp $(OBJIMGFILES) $(MEDIA_SRC_DIR)/v4l/*.svg $(MEDIA_OBJ_DIR)/media_api
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$(MEDIA_OBJ_DIR)/%: $(MEDIA_SRC_DIR)/%.b64
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$(Q)base64 -d $< >$@
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@ -2417,6 +2417,11 @@ details.</para>
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<para>Added integer menus, the new type will be
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V4L2_CTRL_TYPE_INTEGER_MENU.</para>
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</listitem>
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<listitem>
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<para>Added selection API for V4L2 subdev interface:
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&VIDIOC-SUBDEV-G-SELECTION; and
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&VIDIOC-SUBDEV-S-SELECTION;.</para>
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</listitem>
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</orderedlist>
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</section>
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@ -2533,6 +2538,10 @@ ioctls.</para>
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<listitem>
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<para>Selection API. <xref linkend="selection-api" /></para>
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</listitem>
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<listitem>
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<para>Sub-device selection API: &VIDIOC-SUBDEV-G-SELECTION;
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and &VIDIOC-SUBDEV-S-SELECTION; ioctls.</para>
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</listitem>
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</itemizedlist>
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</section>
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@ -76,11 +76,12 @@
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<wordasword>format</wordasword> means the combination of media bus data
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format, frame width and frame height.</para></note>
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<para>Image formats are typically negotiated on video capture and output
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devices using the <link linkend="crop">cropping and scaling</link> ioctls.
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The driver is responsible for configuring every block in the video pipeline
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according to the requested format at the pipeline input and/or
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output.</para>
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<para>Image formats are typically negotiated on video capture and
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output devices using the format and <link
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linkend="vidioc-subdev-g-selection">selection</link> ioctls. The
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driver is responsible for configuring every block in the video
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pipeline according to the requested format at the pipeline input
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and/or output.</para>
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<para>For complex devices, such as often found in embedded systems,
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identical image sizes at the output of a pipeline can be achieved using
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@ -276,11 +277,11 @@
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</section>
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<section>
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<title>Cropping and scaling</title>
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<title>Selections: cropping, scaling and composition</title>
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<para>Many sub-devices support cropping frames on their input or output
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pads (or possible even on both). Cropping is used to select the area of
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interest in an image, typically on a video sensor or video decoder. It can
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interest in an image, typically on an image sensor or a video decoder. It can
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also be used as part of digital zoom implementations to select the area of
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the image that will be scaled up.</para>
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@ -288,26 +289,179 @@
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&v4l2-rect; by the coordinates of the top left corner and the rectangle
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size. Both the coordinates and sizes are expressed in pixels.</para>
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<para>The crop rectangle is retrieved and set using the
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&VIDIOC-SUBDEV-G-CROP; and &VIDIOC-SUBDEV-S-CROP; ioctls. Like for pad
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formats, drivers store try and active crop rectangles. The format
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negotiation mechanism applies to crop settings as well.</para>
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<para>As for pad formats, drivers store try and active
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rectangles for the selection targets of ACTUAL type <xref
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linkend="v4l2-subdev-selection-targets">.</xref></para>
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<para>On input pads, cropping is applied relatively to the current pad
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format. The pad format represents the image size as received by the
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sub-device from the previous block in the pipeline, and the crop rectangle
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represents the sub-image that will be transmitted further inside the
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sub-device for processing. The crop rectangle be entirely containted
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inside the input image size.</para>
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<para>On sink pads, cropping is applied relative to the
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current pad format. The pad format represents the image size as
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received by the sub-device from the previous block in the
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pipeline, and the crop rectangle represents the sub-image that
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will be transmitted further inside the sub-device for
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processing.</para>
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<para>Input crop rectangle are reset to their default value when the input
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image format is modified. Drivers should use the input image size as the
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crop rectangle default value, but hardware requirements may prevent this.
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</para>
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<para>The scaling operation changes the size of the image by
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scaling it to new dimensions. The scaling ratio isn't specified
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explicitly, but is implied from the original and scaled image
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sizes. Both sizes are represented by &v4l2-rect;.</para>
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<para>Cropping behaviour on output pads is not defined.</para>
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<para>Scaling support is optional. When supported by a subdev,
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the crop rectangle on the subdev's sink pad is scaled to the
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size configured using the &VIDIOC-SUBDEV-S-SELECTION; IOCTL
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using <constant>V4L2_SUBDEV_SEL_COMPOSE_ACTUAL</constant>
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selection target on the same pad. If the subdev supports scaling
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but not composing, the top and left values are not used and must
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always be set to zero.</para>
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<para>On source pads, cropping is similar to sink pads, with the
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exception that the source size from which the cropping is
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performed, is the COMPOSE rectangle on the sink pad. In both
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sink and source pads, the crop rectangle must be entirely
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contained inside the source image size for the crop
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operation.</para>
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<para>The drivers should always use the closest possible
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rectangle the user requests on all selection targets, unless
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specifically told otherwise.
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<constant>V4L2_SUBDEV_SEL_FLAG_SIZE_GE</constant> and
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<constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant> flags may be
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used to round the image size either up or down. <xref
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linkend="v4l2-subdev-selection-flags"></xref></para>
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</section>
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<section>
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<title>Types of selection targets</title>
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<section>
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<title>ACTUAL targets</title>
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<para>ACTUAL targets reflect the actual hardware configuration
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at any point of time. There is a BOUNDS target
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corresponding to every ACTUAL.</para>
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</section>
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<section>
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<title>BOUNDS targets</title>
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<para>BOUNDS targets is the smallest rectangle that contains
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all valid ACTUAL rectangles. It may not be possible to set the
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ACTUAL rectangle as large as the BOUNDS rectangle, however.
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This may be because e.g. a sensor's pixel array is not
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rectangular but cross-shaped or round. The maximum size may
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also be smaller than the BOUNDS rectangle.</para>
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</section>
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</section>
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<section>
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<title>Order of configuration and format propagation</title>
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<para>Inside subdevs, the order of image processing steps will
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always be from the sink pad towards the source pad. This is also
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reflected in the order in which the configuration must be
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performed by the user: the changes made will be propagated to
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any subsequent stages. If this behaviour is not desired, the
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user must set
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<constant>V4L2_SUBDEV_SEL_FLAG_KEEP_CONFIG</constant> flag. This
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flag causes no propagation of the changes are allowed in any
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circumstances. This may also cause the accessed rectangle to be
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adjusted by the driver, depending on the properties of the
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underlying hardware.</para>
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<para>The coordinates to a step always refer to the actual size
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of the previous step. The exception to this rule is the source
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compose rectangle, which refers to the sink compose bounds
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rectangle --- if it is supported by the hardware.</para>
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<orderedlist>
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<listitem>Sink pad format. The user configures the sink pad
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format. This format defines the parameters of the image the
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entity receives through the pad for further processing.</listitem>
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<listitem>Sink pad actual crop selection. The sink pad crop
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defines the crop performed to the sink pad format.</listitem>
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<listitem>Sink pad actual compose selection. The size of the
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sink pad compose rectangle defines the scaling ratio compared
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to the size of the sink pad crop rectangle. The location of
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the compose rectangle specifies the location of the actual
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sink compose rectangle in the sink compose bounds
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rectangle.</listitem>
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<listitem>Source pad actual crop selection. Crop on the source
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pad defines crop performed to the image in the sink compose
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bounds rectangle.</listitem>
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<listitem>Source pad format. The source pad format defines the
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output pixel format of the subdev, as well as the other
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parameters with the exception of the image width and height.
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Width and height are defined by the size of the source pad
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actual crop selection.</listitem>
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</orderedlist>
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<para>Accessing any of the above rectangles not supported by the
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subdev will return <constant>EINVAL</constant>. Any rectangle
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referring to a previous unsupported rectangle coordinates will
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instead refer to the previous supported rectangle. For example,
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if sink crop is not supported, the compose selection will refer
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to the sink pad format dimensions instead.</para>
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<figure id="subdev-image-processing-crop">
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<title>Image processing in subdevs: simple crop example</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="subdev-image-processing-crop.svg"
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format="SVG" scale="200" />
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</imageobject>
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</mediaobject>
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</figure>
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<para>In the above example, the subdev supports cropping on its
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sink pad. To configure it, the user sets the media bus format on
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the subdev's sink pad. Now the actual crop rectangle can be set
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on the sink pad --- the location and size of this rectangle
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reflect the location and size of a rectangle to be cropped from
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the sink format. The size of the sink crop rectangle will also
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be the size of the format of the subdev's source pad.</para>
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<figure id="subdev-image-processing-scaling-multi-source">
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<title>Image processing in subdevs: scaling with multiple sources</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="subdev-image-processing-scaling-multi-source.svg"
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format="SVG" scale="200" />
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</imageobject>
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</mediaobject>
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</figure>
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<para>In this example, the subdev is capable of first cropping,
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then scaling and finally cropping for two source pads
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individually from the resulting scaled image. The location of
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the scaled image in the cropped image is ignored in sink compose
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target. Both of the locations of the source crop rectangles
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refer to the sink scaling rectangle, independently cropping an
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area at location specified by the source crop rectangle from
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it.</para>
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<figure id="subdev-image-processing-full">
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<title>Image processing in subdevs: scaling and composition
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with multiple sinks and sources</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="subdev-image-processing-full.svg"
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format="SVG" scale="200" />
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</imageobject>
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</mediaobject>
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</figure>
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<para>The subdev driver supports two sink pads and two source
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pads. The images from both of the sink pads are individually
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cropped, then scaled and further composed on the composition
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bounds rectangle. From that, two independent streams are cropped
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and sent out of the subdev from the source pads.</para>
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</section>
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</section>
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&sub-subdev-formats;
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@ -96,6 +96,17 @@ Remote Controller chapter.</contrib>
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</address>
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</affiliation>
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</author>
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<author>
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<firstname>Sakari</firstname>
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<surname>Ailus</surname>
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<contrib>Subdev selections API.</contrib>
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<affiliation>
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<address>
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<email>sakari.ailus@iki.fi</email>
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</address>
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</affiliation>
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</author>
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</authorgroup>
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<copyright>
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@ -131,7 +142,8 @@ applications. -->
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<revnumber>3.5</revnumber>
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<date>2012-04-02</date>
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<authorinitials>sa</authorinitials>
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<revremark>Added V4L2_CTRL_TYPE_INTEGER_MENU.
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<revremark>Added V4L2_CTRL_TYPE_INTEGER_MENU and V4L2 subdev
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selections API.
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</revremark>
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</revision>
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@ -548,6 +560,7 @@ and discussions on the V4L mailing list.</revremark>
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&sub-subdev-g-crop;
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&sub-subdev-g-fmt;
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&sub-subdev-g-frame-interval;
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&sub-subdev-g-selection;
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&sub-subscribe-event;
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<!-- End of ioctls. -->
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&sub-mmap;
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@ -0,0 +1,228 @@
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<refentry id="vidioc-subdev-g-selection">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_SUBDEV_G_SELECTION, VIDIOC_SUBDEV_S_SELECTION</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_SUBDEV_G_SELECTION</refname>
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<refname>VIDIOC_SUBDEV_S_SELECTION</refname>
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<refpurpose>Get or set selection rectangles on a subdev pad</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_subdev_selection *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_SUBDEV_G_SELECTION, VIDIOC_SUBDEV_S_SELECTION</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<note>
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<title>Experimental</title>
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<para>This is an <link linkend="experimental">experimental</link>
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interface and may change in the future.</para>
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</note>
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<para>The selections are used to configure various image
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processing functionality performed by the subdevs which affect the
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image size. This currently includes cropping, scaling and
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composition.</para>
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<para>The selection API replaces <link
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linkend="vidioc-subdev-g-crop">the old subdev crop API</link>. All
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the function of the crop API, and more, are supported by the
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selections API.</para>
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<para>See <xref linkend="subdev"></xref> for
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more information on how each selection target affects the image
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processing pipeline inside the subdevice.</para>
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<section>
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<title>Types of selection targets</title>
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<para>There are two types of selection targets: actual and bounds.
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The ACTUAL targets are the targets which configure the hardware.
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The BOUNDS target will return a rectangle that contain all
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possible ACTUAL rectangles.</para>
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</section>
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<section>
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<title>Discovering supported features</title>
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<para>To discover which targets are supported, the user can
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perform <constant>VIDIOC_SUBDEV_G_SELECTION</constant> on them.
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Any unsupported target will return
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<constant>EINVAL</constant>.</para>
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</section>
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<table pgwide="1" frame="none" id="v4l2-subdev-selection-targets">
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<title>V4L2 subdev selection targets</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_SUBDEV_SEL_TGT_CROP_ACTUAL</constant></entry>
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<entry>0x0000</entry>
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<entry>Actual crop. Defines the cropping
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performed by the processing step.</entry>
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</row>
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<row>
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<entry><constant>V4L2_SUBDEV_SEL_TGT_CROP_BOUNDS</constant></entry>
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<entry>0x0002</entry>
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<entry>Bounds of the crop rectangle.</entry>
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</row>
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<row>
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<entry><constant>V4L2_SUBDEV_SEL_TGT_COMPOSE_ACTUAL</constant></entry>
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<entry>0x0100</entry>
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<entry>Actual compose rectangle. Used to configure scaling
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on sink pads and composition on source pads.</entry>
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</row>
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<row>
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<entry><constant>V4L2_SUBDEV_SEL_TGT_COMPOSE_BOUNDS</constant></entry>
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<entry>0x0102</entry>
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<entry>Bounds of the compose rectangle.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-subdev-selection-flags">
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<title>V4L2 subdev selection flags</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_SUBDEV_SEL_FLAG_SIZE_GE</constant></entry>
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<entry>(1 << 0)</entry> <entry>Suggest the driver it
|
||||
should choose greater or equal rectangle (in size) than
|
||||
was requested. Albeit the driver may choose a lesser size,
|
||||
it will only do so due to hardware limitations. Without
|
||||
this flag (and
|
||||
<constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant>) the
|
||||
behaviour is to choose the closest possible
|
||||
rectangle.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry><constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant></entry>
|
||||
<entry>(1 << 1)</entry> <entry>Suggest the driver it
|
||||
should choose lesser or equal rectangle (in size) than was
|
||||
requested. Albeit the driver may choose a greater size, it
|
||||
will only do so due to hardware limitations.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry><constant>V4L2_SUBDEV_SEL_FLAG_KEEP_CONFIG</constant></entry>
|
||||
<entry>(1 << 2)</entry>
|
||||
<entry>The configuration should not be propagated to any
|
||||
further processing steps. If this flag is not given, the
|
||||
configuration is propagated inside the subdevice to all
|
||||
further processing steps.</entry>
|
||||
</row>
|
||||
</tbody>
|
||||
</tgroup>
|
||||
</table>
|
||||
|
||||
<table pgwide="1" frame="none" id="v4l2-subdev-selection">
|
||||
<title>struct <structname>v4l2_subdev_selection</structname></title>
|
||||
<tgroup cols="3">
|
||||
&cs-str;
|
||||
<tbody valign="top">
|
||||
<row>
|
||||
<entry>__u32</entry>
|
||||
<entry><structfield>which</structfield></entry>
|
||||
<entry>Active or try selection, from
|
||||
&v4l2-subdev-format-whence;.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>__u32</entry>
|
||||
<entry><structfield>pad</structfield></entry>
|
||||
<entry>Pad number as reported by the media framework.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>__u32</entry>
|
||||
<entry><structfield>target</structfield></entry>
|
||||
<entry>Target selection rectangle. See
|
||||
<xref linkend="v4l2-subdev-selection-targets">.</xref>.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>__u32</entry>
|
||||
<entry><structfield>flags</structfield></entry>
|
||||
<entry>Flags. See
|
||||
<xref linkend="v4l2-subdev-selection-flags">.</xref></entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>&v4l2-rect;</entry>
|
||||
<entry><structfield>rect</structfield></entry>
|
||||
<entry>Selection rectangle, in pixels.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>__u32</entry>
|
||||
<entry><structfield>reserved</structfield>[8]</entry>
|
||||
<entry>Reserved for future extensions. Applications and drivers must
|
||||
set the array to zero.</entry>
|
||||
</row>
|
||||
</tbody>
|
||||
</tgroup>
|
||||
</table>
|
||||
|
||||
</refsect1>
|
||||
|
||||
<refsect1>
|
||||
&return-value;
|
||||
|
||||
<variablelist>
|
||||
<varlistentry>
|
||||
<term><errorcode>EBUSY</errorcode></term>
|
||||
<listitem>
|
||||
<para>The selection rectangle can't be changed because the
|
||||
pad is currently busy. This can be caused, for instance, by
|
||||
an active video stream on the pad. The ioctl must not be
|
||||
retried without performing another action to fix the problem
|
||||
first. Only returned by
|
||||
<constant>VIDIOC_SUBDEV_S_SELECTION</constant></para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
<varlistentry>
|
||||
<term><errorcode>EINVAL</errorcode></term>
|
||||
<listitem>
|
||||
<para>The &v4l2-subdev-selection;
|
||||
<structfield>pad</structfield> references a non-existing
|
||||
pad, the <structfield>which</structfield> field references a
|
||||
non-existing format, or the selection target is not
|
||||
supported on the given subdev pad.</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
</variablelist>
|
||||
</refsect1>
|
||||
</refentry>
|
||||
Reference in New Issue