Lines Matching +full:on +full:- +full:device
1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
6 Sub-device Interface
13 components as software blocks called sub-devices.
15 V4L2 sub-devices are usually kernel-only objects. If the V4L2 driver
16 implements the media device API, they will automatically inherit from
17 media entities. Applications will be able to enumerate the sub-devices
21 In addition to make sub-devices discoverable, drivers can also choose to
23 sub-device driver and the V4L2 device driver support this, sub-devices
24 will feature a character device node on which ioctls can be called to
26 - query, read and write sub-devices controls
28 - subscribe and unsubscribe to events and retrieve them
30 - negotiate image formats on individual pads
32 Sub-device character device nodes, conventionally named
33 ``/dev/v4l-subdev*``, use major number 81.
35 Drivers may opt to limit the sub-device character devices to only expose
36 operations that do not modify the device state. In such a case the sub-devices
37 are referred to as ``read-only`` in the rest of this documentation, and the
44 Most V4L2 controls are implemented by sub-device hardware. Drivers
45 usually merge all controls and expose them through video device nodes.
46 Applications can control all sub-devices through a single interface.
53 single device, all but one of the identical controls are hidden.
55 Applications can access those hidden controls through the sub-device
57 behave identically as when issued on V4L2 device nodes, with the
59 sub-device.
61 Depending on the driver, those controls might also be exposed through
62 one (or several) V4L2 device nodes.
68 V4L2 sub-devices can notify applications of events as described in
69 :ref:`event`. The API behaves identically as when used on V4L2 device
71 the sub-device. Depending on the driver, those events might also be
72 reported on one (or several) V4L2 device nodes.
75 .. _pad-level-formats:
77 Pad-level Formats
82 Pad-level formats are only applicable to very complex devices that
83 need to expose low-level format configuration to user space. Generic
92 Image formats are typically negotiated on video capture and output
100 hardware configurations. One such example is shown on
101 :ref:`pipeline-scaling`, where image scaling can be performed on both
105 .. _pipeline-scaling:
107 .. kernel-figure:: pipeline.dot
111 Image Format Negotiation on Pipelines
118 scaling on the sensor is required to achieve higher frame rates.
119 Depending on the use case (quality vs. speed), the pipeline must be
123 Drivers that implement the :ref:`media API <media-controller-intro>`
124 can expose pad-level image format configuration to applications. When
128 negotiate formats on a per-pad basis.
130 Applications are responsible for configuring coherent parameters on the
136 Pad-level image format configuration support can be tested by calling
137 the :ref:`VIDIOC_SUBDEV_G_FMT` ioctl on pad
138 0. If the driver returns an ``EINVAL`` error code pad-level format
139 configuration is not supported by the sub-device.
143 ------------------
145 Acceptable formats on pads can (and usually do) depend on a number of
146 external parameters, such as formats on other pads, active links, or
147 even controls. Finding a combination of formats on all pads in a video
148 pipeline, acceptable to both application and driver, can't rely on
155 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctls operate on
157 configuration. Modifying those 'try' formats leaves the device state
159 and the hardware state stored in the device itself).
161 While not kept as part of the device state, try formats are stored in
162 the sub-device file handles. A
164 the last try format set *on the same sub-device file handle*. Several
165 applications querying the same sub-device at the same time will thus not
168 To find out whether a particular format is supported by the device,
171 verify and, if needed, change the requested ``format`` based on device
177 guaranteed to be supported by the device. In particular, drivers
179 to an :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` call as-is
180 (as long as external parameters, such as formats on other pads or links'
183 Drivers automatically propagate formats inside sub-devices. When a try
184 or active format is set on a pad, corresponding formats on other pads of
185 the same sub-device can be modified by the driver. Drivers are free to
186 modify formats as required by the device. However, they should comply
189 - Formats should be propagated from sink pads to source pads. Modifying
190 a format on a source pad should not modify the format on any sink
193 - Sub-devices that scale frames using variable scaling factors should
199 propagating them from one sub-device file handle to another.
201 explicitly with compatible formats. Identical formats on the two ends of
203 different formats matching device requirements as being compatible.
205 :ref:`sample-pipeline-config` shows a sample configuration sequence
206 for the pipeline described in :ref:`pipeline-scaling` (table columns
216 .. _sample-pipeline-config:
218 .. flat-table:: Sample Pipeline Configuration
219 :header-rows: 1
220 :stub-columns: 0
223 * -
224 - Sensor/0
227 - Frontend/0
230 - Frontend/1
233 - Scaler/0
236 - Scaler/0
239 - Scaler/1
242 * - Initial state
243 - 2048x1536
246 - (default)
247 - (default)
248 - (default)
249 - (default)
250 - (default)
251 * - Configure frontend sink format
252 - 2048x1536
255 - *2048x1536*
258 - *2046x1534*
261 - (default)
262 - (default)
263 - (default)
264 * - Configure scaler sink format
265 - 2048x1536
268 - 2048x1536
271 - 2046x1534
274 - *2046x1534*
277 - *0,0/2046x1534*
278 - *2046x1534*
281 * - Configure scaler sink compose selection
282 - 2048x1536
285 - 2048x1536
288 - 2046x1534
291 - 2046x1534
294 - *0,0/1280x960*
295 - *1280x960*
304 size and V4L2_MBUS_FMT_SGRBG8_1X8 media bus code. Formats on the
306 values, as well as the compose rectangle on the scaler's sink pad.
315 on the sink pad is set to V4L2_MBUS_FMT_SGRBG_1X8. The driver
316 propagates the size to the compose selection rectangle on the
330 be applied as-is by the driver without being modified.
333 .. _v4l2-subdev-selections:
336 ---------------------------------------------
338 Many sub-devices support cropping frames on their input or output pads
339 (or possible even on both). Cropping is used to select the area of
340 interest in an image, typically on an image sensor or a video decoder.
350 selection targets :ref:`v4l2-selections-common`.
352 On sink pads, cropping is applied relative to the current pad format.
353 The pad format represents the image size as received by the sub-device
355 represents the sub-image that will be transmitted further inside the
356 sub-device for processing.
364 rectangle on the subdev's sink pad is scaled to the size configured
367 using ``V4L2_SEL_TGT_COMPOSE`` selection target on the same pad. If the
371 On source pads, cropping is similar to sink pads, with the exception
373 COMPOSE rectangle on the sink pad. In both sink and source pads, the
378 requests on all selection targets, unless specifically told otherwise.
380 the image size either up or down. :ref:`v4l2-selection-flags`
384 --------------------------
401 pixel array is not rectangular but cross-shaped or round. The maximum
406 ---------------------------------------------
415 by the driver, depending on the properties of the underlying hardware.
419 rectangle, which refers to the sink compose bounds rectangle --- if it
435 4. Source pad actual crop selection. Crop on the source pad defines crop
450 .. _subdev-image-processing-crop:
452 .. kernel-figure:: subdev-image-processing-crop.svg
453 :alt: subdev-image-processing-crop.svg
458 In the above example, the subdev supports cropping on its sink pad. To
459 configure it, the user sets the media bus format on the subdev's sink
460 pad. Now the actual crop rectangle can be set on the sink pad --- the
467 .. _subdev-image-processing-scaling-multi-source:
469 .. kernel-figure:: subdev-image-processing-scaling-multi-source.svg
470 :alt: subdev-image-processing-scaling-multi-source.svg
483 .. _subdev-image-processing-full:
485 .. kernel-figure:: subdev-image-processing-full.svg
486 :alt: subdev-image-processing-full.svg
493 further composed on the composition bounds rectangle. From that, two
501 subdev-formats