From 670027c507e99521d416994a18a498def9ef2ea3 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Andr=C3=A9=20Fabian=20Silva=20Delgado?= Date: Sat, 22 Oct 2016 19:31:08 -0300 Subject: Linux-libre 4.8.3-gnu --- Documentation/DocBook/media/v4l/dev-subdev.xml | 478 ------------------------- 1 file changed, 478 deletions(-) delete mode 100644 Documentation/DocBook/media/v4l/dev-subdev.xml (limited to 'Documentation/DocBook/media/v4l/dev-subdev.xml') diff --git a/Documentation/DocBook/media/v4l/dev-subdev.xml b/Documentation/DocBook/media/v4l/dev-subdev.xml deleted file mode 100644 index f4bc27af8..000000000 --- a/Documentation/DocBook/media/v4l/dev-subdev.xml +++ /dev/null @@ -1,478 +0,0 @@ - Sub-device Interface - - The complex nature of V4L2 devices, where hardware is often made of - several integrated circuits that need to interact with each other in a - controlled way, leads to complex V4L2 drivers. The drivers usually reflect - the hardware model in software, and model the different hardware components - as software blocks called sub-devices. - - V4L2 sub-devices are usually kernel-only objects. If the V4L2 driver - implements the media device API, they will automatically inherit from media - entities. Applications will be able to enumerate the sub-devices and discover - the hardware topology using the media entities, pads and links enumeration - API. - - In addition to make sub-devices discoverable, drivers can also choose - to make them directly configurable by applications. When both the sub-device - driver and the V4L2 device driver support this, sub-devices will feature a - character device node on which ioctls can be called to - - query, read and write sub-devices controls - subscribe and unsubscribe to events and retrieve them - negotiate image formats on individual pads - - - - Sub-device character device nodes, conventionally named - /dev/v4l-subdev*, use major number 81. - -
- Controls - Most V4L2 controls are implemented by sub-device hardware. Drivers - usually merge all controls and expose them through video device nodes. - Applications can control all sub-devices through a single interface. - - Complex devices sometimes implement the same control in different - pieces of hardware. This situation is common in embedded platforms, where - both sensors and image processing hardware implement identical functions, - such as contrast adjustment, white balance or faulty pixels correction. As - the V4L2 controls API doesn't support several identical controls in a single - device, all but one of the identical controls are hidden. - - Applications can access those hidden controls through the sub-device - node with the V4L2 control API described in . The - ioctls behave identically as when issued on V4L2 device nodes, with the - exception that they deal only with controls implemented in the sub-device. - - - Depending on the driver, those controls might also be exposed through - one (or several) V4L2 device nodes. -
- -
- Events - V4L2 sub-devices can notify applications of events as described in - . The API behaves identically as when used on V4L2 - device nodes, with the exception that it only deals with events generated by - the sub-device. Depending on the driver, those events might also be reported - on one (or several) V4L2 device nodes. -
- -
- Pad-level Formats - - Pad-level formats are only applicable to very complex device that - need to expose low-level format configuration to user space. Generic V4L2 - applications do not need to use the API described in - this section. - - For the purpose of this section, the term - format means the combination of media bus data - format, frame width and frame height. - - Image formats are typically negotiated on video capture and - output devices using the format and selection ioctls. The - driver is responsible for configuring every block in the video - pipeline according to the requested format at the pipeline input - and/or output. - - For complex devices, such as often found in embedded systems, - identical image sizes at the output of a pipeline can be achieved using - different hardware configurations. One such example is shown on - , where - image scaling can be performed on both the video sensor and the host image - processing hardware. - -
- Image Format Negotiation on Pipelines - - - - - - - - - High quality and high speed pipeline configuration - - -
- - The sensor scaler is usually of less quality than the host scaler, but - scaling on the sensor is required to achieve higher frame rates. Depending - on the use case (quality vs. speed), the pipeline must be configured - differently. Applications need to configure the formats at every point in - the pipeline explicitly. - - Drivers that implement the media - API can expose pad-level image format configuration to applications. - When they do, applications can use the &VIDIOC-SUBDEV-G-FMT; and - &VIDIOC-SUBDEV-S-FMT; ioctls. to negotiate formats on a per-pad basis. - - Applications are responsible for configuring coherent parameters on - the whole pipeline and making sure that connected pads have compatible - formats. The pipeline is checked for formats mismatch at &VIDIOC-STREAMON; - time, and an &EPIPE; is then returned if the configuration is - invalid. - - Pad-level image format configuration support can be tested by calling - the &VIDIOC-SUBDEV-G-FMT; ioctl on pad 0. If the driver returns an &EINVAL; - pad-level format configuration is not supported by the sub-device. - -
- Format Negotiation - - Acceptable formats on pads can (and usually do) depend on a number - of external parameters, such as formats on other pads, active links, or - even controls. Finding a combination of formats on all pads in a video - pipeline, acceptable to both application and driver, can't rely on formats - enumeration only. A format negotiation mechanism is required. - - Central to the format negotiation mechanism are the get/set format - operations. When called with the which argument - set to V4L2_SUBDEV_FORMAT_TRY, the - &VIDIOC-SUBDEV-G-FMT; and &VIDIOC-SUBDEV-S-FMT; ioctls operate on a set of - formats parameters that are not connected to the hardware configuration. - Modifying those 'try' formats leaves the device state untouched (this - applies to both the software state stored in the driver and the hardware - state stored in the device itself). - - While not kept as part of the device state, try formats are stored - in the sub-device file handles. A &VIDIOC-SUBDEV-G-FMT; call will return - the last try format set on the same sub-device file - handle. Several applications querying the same sub-device at - the same time will thus not interact with each other. - - To find out whether a particular format is supported by the device, - applications use the &VIDIOC-SUBDEV-S-FMT; ioctl. Drivers verify and, if - needed, change the requested format based on - device requirements and return the possibly modified value. Applications - can then choose to try a different format or accept the returned value and - continue. - - Formats returned by the driver during a negotiation iteration are - guaranteed to be supported by the device. In particular, drivers guarantee - that a returned format will not be further changed if passed to an - &VIDIOC-SUBDEV-S-FMT; call as-is (as long as external parameters, such as - formats on other pads or links' configuration are not changed). - - Drivers automatically propagate formats inside sub-devices. When a - try or active format is set on a pad, corresponding formats on other pads - of the same sub-device can be modified by the driver. Drivers are free to - modify formats as required by the device. However, they should comply with - the following rules when possible: - - Formats should be propagated from sink pads to source pads. - Modifying a format on a source pad should not modify the format on any - sink pad. - Sub-devices that scale frames using variable scaling factors - should reset the scale factors to default values when sink pads formats - are modified. If the 1:1 scaling ratio is supported, this means that - source pads formats should be reset to the sink pads formats. - - - - Formats are not propagated across links, as that would involve - propagating them from one sub-device file handle to another. Applications - must then take care to configure both ends of every link explicitly with - compatible formats. Identical formats on the two ends of a link are - guaranteed to be compatible. Drivers are free to accept different formats - matching device requirements as being compatible. - - - shows a sample configuration sequence for the pipeline described in - (table - columns list entity names and pad numbers). - - - Sample Pipeline Configuration - - - - - - - - - - - - Sensor/0 format - Frontend/0 format - Frontend/1 format - Scaler/0 format - Scaler/0 compose selection rectangle - Scaler/1 format - - - - - Initial state - 2048x1536/SGRBG8_1X8 - (default) - (default) - (default) - (default) - (default) - - - Configure frontend sink format - 2048x1536/SGRBG8_1X8 - 2048x1536/SGRBG8_1X8 - 2046x1534/SGRBG8_1X8 - (default) - (default) - (default) - - - Configure scaler sink format - 2048x1536/SGRBG8_1X8 - 2048x1536/SGRBG8_1X8 - 2046x1534/SGRBG8_1X8 - 2046x1534/SGRBG8_1X8 - 0,0/2046x1534 - 2046x1534/SGRBG8_1X8 - - - Configure scaler sink compose selection - 2048x1536/SGRBG8_1X8 - 2048x1536/SGRBG8_1X8 - 2046x1534/SGRBG8_1X8 - 2046x1534/SGRBG8_1X8 - 0,0/1280x960 - 1280x960/SGRBG8_1X8 - - - -
- - - - Initial state. The sensor source pad format is - set to its native 3MP size and V4L2_MBUS_FMT_SGRBG8_1X8 - media bus code. Formats on the host frontend and scaler sink - and source pads have the default values, as well as the - compose rectangle on the scaler's sink pad. - - The application configures the frontend sink - pad format's size to 2048x1536 and its media bus code to - V4L2_MBUS_FMT_SGRBG_1X8. The driver propagates the format to - the frontend source pad. - - The application configures the scaler sink pad - format's size to 2046x1534 and the media bus code to - V4L2_MBUS_FMT_SGRBG_1X8 to match the frontend source size and - media bus code. The media bus code on the sink pad is set to - V4L2_MBUS_FMT_SGRBG_1X8. The driver propagates the size to the - compose selection rectangle on the scaler's sink pad, and the - format to the scaler source pad. - - The application configures the size of the compose - selection rectangle of the scaler's sink pad 1280x960. The driver - propagates the size to the scaler's source pad - format. - - - - - When satisfied with the try results, applications can set the active - formats by setting the which argument to - V4L2_SUBDEV_FORMAT_ACTIVE. Active formats are changed - exactly as try formats by drivers. To avoid modifying the hardware state - during format negotiation, applications should negotiate try formats first - and then modify the active settings using the try formats returned during - the last negotiation iteration. This guarantees that the active format - will be applied as-is by the driver without being modified. - -
- -
- Selections: cropping, scaling and composition - - Many sub-devices support cropping frames on their input or output - pads (or possible even on both). Cropping is used to select the area of - interest in an image, typically on an image sensor or a video decoder. It can - also be used as part of digital zoom implementations to select the area of - the image that will be scaled up. - - Crop settings are defined by a crop rectangle and represented in a - &v4l2-rect; by the coordinates of the top left corner and the rectangle - size. Both the coordinates and sizes are expressed in pixels. - - As for pad formats, drivers store try and active - rectangles for the selection targets . - - On sink pads, cropping is applied relative to the - current pad format. The pad format represents the image size as - received by the sub-device from the previous block in the - pipeline, and the crop rectangle represents the sub-image that - will be transmitted further inside the sub-device for - processing. - - The scaling operation changes the size of the image by - scaling it to new dimensions. The scaling ratio isn't specified - explicitly, but is implied from the original and scaled image - sizes. Both sizes are represented by &v4l2-rect;. - - Scaling support is optional. When supported by a subdev, - the crop rectangle on the subdev's sink pad is scaled to the - size configured using the &VIDIOC-SUBDEV-S-SELECTION; IOCTL - using V4L2_SEL_TGT_COMPOSE - selection target on the same pad. If the subdev supports scaling - but not composing, the top and left values are not used and must - always be set to zero. - - On source pads, cropping is similar to sink pads, with the - exception that the source size from which the cropping is - performed, is the COMPOSE rectangle on the sink pad. In both - sink and source pads, the crop rectangle must be entirely - contained inside the source image size for the crop - operation. - - The drivers should always use the closest possible - rectangle the user requests on all selection targets, unless - specifically told otherwise. - V4L2_SEL_FLAG_GE and - V4L2_SEL_FLAG_LE flags may be - used to round the image size either up or down. -
- -
- Types of selection targets - -
- Actual targets - - Actual targets (without a postfix) reflect the actual - hardware configuration at any point of time. There is a BOUNDS - target corresponding to every actual target. -
- -
- BOUNDS targets - - BOUNDS targets is the smallest rectangle that contains all - valid actual rectangles. It may not be possible to set the actual - rectangle as large as the BOUNDS rectangle, however. This may be - because e.g. a sensor's pixel array is not rectangular but - cross-shaped or round. The maximum size may also be smaller than the - BOUNDS rectangle. -
- -
- -
- Order of configuration and format propagation - - Inside subdevs, the order of image processing steps will - always be from the sink pad towards the source pad. This is also - reflected in the order in which the configuration must be - performed by the user: the changes made will be propagated to - any subsequent stages. If this behaviour is not desired, the - user must set - V4L2_SEL_FLAG_KEEP_CONFIG flag. This - flag causes no propagation of the changes are allowed in any - circumstances. This may also cause the accessed rectangle to be - adjusted by the driver, depending on the properties of the - underlying hardware. - - The coordinates to a step always refer to the actual size - of the previous step. The exception to this rule is the source - compose rectangle, which refers to the sink compose bounds - rectangle --- if it is supported by the hardware. - - - Sink pad format. The user configures the sink pad - format. This format defines the parameters of the image the - entity receives through the pad for further processing. - - Sink pad actual crop selection. The sink pad crop - defines the crop performed to the sink pad format. - - Sink pad actual compose selection. The size of the - sink pad compose rectangle defines the scaling ratio compared - to the size of the sink pad crop rectangle. The location of - the compose rectangle specifies the location of the actual - sink compose rectangle in the sink compose bounds - rectangle. - - Source pad actual crop selection. Crop on the source - pad defines crop performed to the image in the sink compose - bounds rectangle. - - Source pad format. The source pad format defines the - output pixel format of the subdev, as well as the other - parameters with the exception of the image width and height. - Width and height are defined by the size of the source pad - actual crop selection. - - - Accessing any of the above rectangles not supported by the - subdev will return EINVAL. Any rectangle - referring to a previous unsupported rectangle coordinates will - instead refer to the previous supported rectangle. For example, - if sink crop is not supported, the compose selection will refer - to the sink pad format dimensions instead. - -
- Image processing in subdevs: simple crop example - - - - - -
- - In the above example, the subdev supports cropping on its - sink pad. To configure it, the user sets the media bus format on - the subdev's sink pad. Now the actual crop rectangle can be set - on the sink pad --- the location and size of this rectangle - reflect the location and size of a rectangle to be cropped from - the sink format. The size of the sink crop rectangle will also - be the size of the format of the subdev's source pad. - -
- Image processing in subdevs: scaling with multiple sources - - - - - -
- - In this example, the subdev is capable of first cropping, - then scaling and finally cropping for two source pads - individually from the resulting scaled image. The location of - the scaled image in the cropped image is ignored in sink compose - target. Both of the locations of the source crop rectangles - refer to the sink scaling rectangle, independently cropping an - area at location specified by the source crop rectangle from - it. - -
- Image processing in subdevs: scaling and composition - with multiple sinks and sources - - - - - -
- - The subdev driver supports two sink pads and two source - pads. The images from both of the sink pads are individually - cropped, then scaled and further composed on the composition - bounds rectangle. From that, two independent streams are cropped - and sent out of the subdev from the source pads. - -
- -
- - &sub-subdev-formats; -- cgit v1.2.3