While the V4L2 selection API and V4L2 subdev selection APIs are very similar, there's one fundamental difference between the two. On sub-device API, the selection rectangle refers to the media bus format, and is bound to a sub-device's pad. On the V4L2 interface the selection rectangles refer to the in-memory pixel format. This section defines the common definitions of the selection interfaces on the two APIs.

The precise meaning of the selection targets may be dependent on which of the two interfaces they are used. &cs-def; Target name id Definition Valid for V4L2 Valid for V4L2 subdev V4L2_SEL_TGT_CROP 0x0000 Crop rectangle. Defines the cropped area. Yes Yes V4L2_SEL_TGT_CROP_DEFAULT 0x0001 Suggested cropping rectangle that covers the "whole picture". Yes No V4L2_SEL_TGT_CROP_BOUNDS 0x0002 Bounds of the crop rectangle. All valid crop rectangles fit inside the crop bounds rectangle. Yes Yes V4L2_SEL_TGT_NATIVE_SIZE 0x0003 The native size of the device, e.g. a sensor's pixel array. left and top fields are zero for this target. Setting the native size will generally only make sense for memory to memory devices where the software can create a canvas of a given size in which for example a video frame can be composed. In that case V4L2_SEL_TGT_NATIVE_SIZE can be used to configure the size of that canvas. Yes Yes V4L2_SEL_TGT_COMPOSE 0x0100 Compose rectangle. Used to configure scaling and composition. Yes Yes V4L2_SEL_TGT_COMPOSE_DEFAULT 0x0101 Suggested composition rectangle that covers the "whole picture". Yes No V4L2_SEL_TGT_COMPOSE_BOUNDS 0x0102 Bounds of the compose rectangle. All valid compose rectangles fit inside the compose bounds rectangle. Yes Yes V4L2_SEL_TGT_COMPOSE_PADDED 0x0103 The active area and all padding pixels that are inserted or modified by hardware. Yes No

&cs-def; Flag name id Definition Valid for V4L2 Valid for V4L2 subdev V4L2_SEL_FLAG_GE (1 << 0) 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 V4L2_SEL_FLAG_LE) the behaviour is to choose the closest possible rectangle. Yes Yes V4L2_SEL_FLAG_LE (1 << 1) 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. Yes Yes V4L2_SEL_FLAG_KEEP_CONFIG (1 << 2) The configuration must 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. No Yes