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diff --git a/Documentation/DocBook/media/v4l/dev-subdev.xml b/Documentation/DocBook/media/v4l/dev-subdev.xml deleted file mode 100644 index f4bc27af83eb..000000000000 --- a/Documentation/DocBook/media/v4l/dev-subdev.xml +++ /dev/null @@ -1,478 +0,0 @@ - <title>Sub-device Interface</title> - - <para>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.</para> - - <para>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.</para> - - <para>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 - <itemizedlist> - <listitem><para>query, read and write sub-devices controls</para></listitem> - <listitem><para>subscribe and unsubscribe to events and retrieve them</para></listitem> - <listitem><para>negotiate image formats on individual pads</para></listitem> - </itemizedlist> - </para> - - <para>Sub-device character device nodes, conventionally named - <filename>/dev/v4l-subdev*</filename>, use major number 81.</para> - - <section> - <title>Controls</title> - <para>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.</para> - - <para>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.</para> - - <para>Applications can access those hidden controls through the sub-device - node with the V4L2 control API described in <xref linkend="control" />. 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. - </para> - - <para>Depending on the driver, those controls might also be exposed through - one (or several) V4L2 device nodes.</para> - </section> - - <section> - <title>Events</title> - <para>V4L2 sub-devices can notify applications of events as described in - <xref linkend="event" />. 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.</para> - </section> - - <section id="pad-level-formats"> - <title>Pad-level Formats</title> - - <warning><para>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 <emphasis>not</emphasis> need to use the API described in - this section.</para></warning> - - <note><para>For the purpose of this section, the term - <wordasword>format</wordasword> means the combination of media bus data - format, frame width and frame height.</para></note> - - <para>Image formats are typically negotiated on video capture and - output devices using the format and <link - linkend="vidioc-subdev-g-selection">selection</link> 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.</para> - - <para>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 - <xref linkend="pipeline-scaling" />, where - image scaling can be performed on both the video sensor and the host image - processing hardware.</para> - - <figure id="pipeline-scaling"> - <title>Image Format Negotiation on Pipelines</title> - <mediaobject> - <imageobject> - <imagedata fileref="pipeline.pdf" format="PS" /> - </imageobject> - <imageobject> - <imagedata fileref="pipeline.png" format="PNG" /> - </imageobject> - <textobject> - <phrase>High quality and high speed pipeline configuration</phrase> - </textobject> - </mediaobject> - </figure> - - <para>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.</para> - - <para>Drivers that implement the <link linkend="media-controller-intro">media - API</link> 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.</para> - - <para>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.</para> - - <para>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.</para> - - <section> - <title>Format Negotiation</title> - - <para>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.</para> - - <para>Central to the format negotiation mechanism are the get/set format - operations. When called with the <structfield>which</structfield> argument - set to <constant>V4L2_SUBDEV_FORMAT_TRY</constant>, 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).</para> - - <para>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 <emphasis>on the same sub-device file - handle</emphasis>. Several applications querying the same sub-device at - the same time will thus not interact with each other.</para> - - <para>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 <structfield>format</structfield> 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.</para> - - <para>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).</para> - - <para>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: - <itemizedlist> - <listitem><para>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.</para></listitem> - <listitem><para>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.</para></listitem> - </itemizedlist> - </para> - - <para>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.</para> - - <para><xref linkend="sample-pipeline-config" /> - shows a sample configuration sequence for the pipeline described in - <xref linkend="pipeline-scaling" /> (table - columns list entity names and pad numbers).</para> - - <table pgwide="0" frame="none" id="sample-pipeline-config"> - <title>Sample Pipeline Configuration</title> - <tgroup cols="3"> - <colspec colname="what"/> - <colspec colname="sensor-0 format" /> - <colspec colname="frontend-0 format" /> - <colspec colname="frontend-1 format" /> - <colspec colname="scaler-0 format" /> - <colspec colname="scaler-0 compose" /> - <colspec colname="scaler-1 format" /> - <thead> - <row> - <entry></entry> - <entry>Sensor/0 format</entry> - <entry>Frontend/0 format</entry> - <entry>Frontend/1 format</entry> - <entry>Scaler/0 format</entry> - <entry>Scaler/0 compose selection rectangle</entry> - <entry>Scaler/1 format</entry> - </row> - </thead> - <tbody valign="top"> - <row> - <entry>Initial state</entry> - <entry>2048x1536/SGRBG8_1X8</entry> - <entry>(default)</entry> - <entry>(default)</entry> - <entry>(default)</entry> - <entry>(default)</entry> - <entry>(default)</entry> - </row> - <row> - <entry>Configure frontend sink format</entry> - <entry>2048x1536/SGRBG8_1X8</entry> - <entry><emphasis>2048x1536/SGRBG8_1X8</emphasis></entry> - <entry><emphasis>2046x1534/SGRBG8_1X8</emphasis></entry> - <entry>(default)</entry> - <entry>(default)</entry> - <entry>(default)</entry> - </row> - <row> - <entry>Configure scaler sink format</entry> - <entry>2048x1536/SGRBG8_1X8</entry> - <entry>2048x1536/SGRBG8_1X8</entry> - <entry>2046x1534/SGRBG8_1X8</entry> - <entry><emphasis>2046x1534/SGRBG8_1X8</emphasis></entry> - <entry><emphasis>0,0/2046x1534</emphasis></entry> - <entry><emphasis>2046x1534/SGRBG8_1X8</emphasis></entry> - </row> - <row> - <entry>Configure scaler sink compose selection</entry> - <entry>2048x1536/SGRBG8_1X8</entry> - <entry>2048x1536/SGRBG8_1X8</entry> - <entry>2046x1534/SGRBG8_1X8</entry> - <entry>2046x1534/SGRBG8_1X8</entry> - <entry><emphasis>0,0/1280x960</emphasis></entry> - <entry><emphasis>1280x960/SGRBG8_1X8</emphasis></entry> - </row> - </tbody> - </tgroup> - </table> - - <para> - <orderedlist> - <listitem><para>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.</para></listitem> - - <listitem><para>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.</para></listitem> - - <listitem><para>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.</para></listitem> - - <listitem><para>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.</para></listitem> - - </orderedlist> - </para> - - <para>When satisfied with the try results, applications can set the active - formats by setting the <structfield>which</structfield> argument to - <constant>V4L2_SUBDEV_FORMAT_ACTIVE</constant>. 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. - </para> - </section> - - <section id="v4l2-subdev-selections"> - <title>Selections: cropping, scaling and composition</title> - - <para>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.</para> - - <para>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.</para> - - <para>As for pad formats, drivers store try and active - rectangles for the selection targets <xref - linkend="v4l2-selections-common" />.</para> - - <para>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.</para> - - <para>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;.</para> - - <para>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 <constant>V4L2_SEL_TGT_COMPOSE</constant> - 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.</para> - - <para>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.</para> - - <para>The drivers should always use the closest possible - rectangle the user requests on all selection targets, unless - specifically told otherwise. - <constant>V4L2_SEL_FLAG_GE</constant> and - <constant>V4L2_SEL_FLAG_LE</constant> flags may be - used to round the image size either up or down. <xref - linkend="v4l2-selection-flags" /></para> - </section> - - <section> - <title>Types of selection targets</title> - - <section> - <title>Actual targets</title> - - <para>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.</para> - </section> - - <section> - <title>BOUNDS targets</title> - - <para>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.</para> - </section> - - </section> - - <section> - <title>Order of configuration and format propagation</title> - - <para>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 - <constant>V4L2_SEL_FLAG_KEEP_CONFIG</constant> 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.</para> - - <para>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.</para> - - <orderedlist> - <listitem><para>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.</para></listitem> - - <listitem><para>Sink pad actual crop selection. The sink pad crop - defines the crop performed to the sink pad format.</para></listitem> - - <listitem><para>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.</para></listitem> - - <listitem><para>Source pad actual crop selection. Crop on the source - pad defines crop performed to the image in the sink compose - bounds rectangle.</para></listitem> - - <listitem><para>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.</para></listitem> - </orderedlist> - - <para>Accessing any of the above rectangles not supported by the - subdev will return <constant>EINVAL</constant>. 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.</para> - - <figure id="subdev-image-processing-crop"> - <title>Image processing in subdevs: simple crop example</title> - <mediaobject> - <imageobject> - <imagedata fileref="subdev-image-processing-crop.svg" - format="SVG" scale="200" /> - </imageobject> - </mediaobject> - </figure> - - <para>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.</para> - - <figure id="subdev-image-processing-scaling-multi-source"> - <title>Image processing in subdevs: scaling with multiple sources</title> - <mediaobject> - <imageobject> - <imagedata fileref="subdev-image-processing-scaling-multi-source.svg" - format="SVG" scale="200" /> - </imageobject> - </mediaobject> - </figure> - - <para>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.</para> - - <figure id="subdev-image-processing-full"> - <title>Image processing in subdevs: scaling and composition - with multiple sinks and sources</title> - <mediaobject> - <imageobject> - <imagedata fileref="subdev-image-processing-full.svg" - format="SVG" scale="200" /> - </imageobject> - </mediaobject> - </figure> - - <para>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.</para> - - </section> - - </section> - - &sub-subdev-formats; |