Lines Matching +full:sub +full:- +full:nodes
1 .. SPDX-License-Identifier: GPL-2.0
3 V4L2 sub-devices
4 ----------------
6 Many drivers need to communicate with sub-devices. These devices can do all
8 encoding or decoding. For webcams common sub-devices are sensors and camera
12 driver with a consistent interface to these sub-devices the
13 :c:type:`v4l2_subdev` struct (v4l2-subdev.h) was created.
15 Each sub-device driver must have a :c:type:`v4l2_subdev` struct. This struct
16 can be stand-alone for simple sub-devices or it might be embedded in a larger
18 low-level device struct (e.g. ``i2c_client``) that contains the device data as
21 it easy to go from a :c:type:`v4l2_subdev` to the actual low-level bus-specific
24 You also need a way to go from the low-level struct to :c:type:`v4l2_subdev`.
29 Bridges might also need to store per-subdev private data, such as a pointer to
30 bridge-specific per-subdev private data. The :c:type:`v4l2_subdev` structure
34 From the bridge driver perspective, you load the sub-device module and somehow
37 Helper functions exist for sub-devices on an I2C bus that do most of this
40 Each :c:type:`v4l2_subdev` contains function pointers that sub-device drivers
41 can implement (or leave ``NULL`` if it is not applicable). Since sub-devices can
46 The top-level ops struct contains pointers to the category ops structs, which
51 .. code-block:: c
84 depending on the sub-device. E.g. a video device is unlikely to support the
90 A sub-device driver initializes the :c:type:`v4l2_subdev` struct using:
96 Afterwards you need to initialize :c:type:`sd <v4l2_subdev>`->name with a
105 .. code-block:: c
107 struct media_pad *pads = &my_sd->pads;
110 err = media_entity_pads_init(&sd->entity, npads, pads);
119 Don't forget to cleanup the media entity before the sub-device is destroyed:
121 .. code-block:: c
123 media_entity_cleanup(&sd->entity);
125 If a sub-device driver implements sink pads, the subdev driver may set the
130 between sub-devices and video nodes.
154 in DT as I2C device nodes. The API used in this second case is described further
158 run-time bridge-subdevice interaction is in both cases the same.
167 After this function was called successfully the subdev->dev field points to
170 If the v4l2_device parent device has a non-NULL mdev field, the sub-device
173 You can unregister a sub-device using:
180 :c:type:`sd <v4l2_subdev>`->dev == ``NULL``.
186 the driver might decide to return ``-EPROBE_DEFER`` to request further reprobing
209 registering their async sub-devices with the notifier.
212 sensor drivers registering their own async sub-device, but it also registers a
213 notifier and further registers async sub-devices for lens and flash devices
214 found in firmware. The notifier for the sub-device is unregistered with the
215 async sub-device.
217 These functions allocate an async sub-device descriptor which is of type struct
218 :c:type:`v4l2_async_subdev` embedded in a driver-specific struct. The &struct
221 .. code-block:: c
246 Drivers can store any type of custom data in their driver-specific
264 .. code-block:: c
266 err = sd->ops->core->g_std(sd, &norm);
270 .. code-block:: c
274 The macro will do the right ``NULL`` pointer checks and returns ``-ENODEV``
275 if :c:type:`sd <v4l2_subdev>` is ``NULL``, ``-ENOIOCTLCMD`` if either
276 :c:type:`sd <v4l2_subdev>`->core or :c:type:`sd <v4l2_subdev>`->core->g_std is ``NULL``, or the act…
277 :c:type:`sd <v4l2_subdev>`->ops->core->g_std ops.
279 It is also possible to call all or a subset of the sub-devices:
281 .. code-block:: c
288 .. code-block:: c
292 Any error except ``-ENOIOCTLCMD`` will exit the loop with that error. If no
293 errors (except ``-ENOIOCTLCMD``) occurred, then 0 is returned.
296 called. If non-zero, then only those whose group ID match that value will
298 :c:type:`sd <v4l2_subdev>`->grp_id to whatever value it wants (it's 0 by
299 default). This value is owned by the bridge driver and the sub-device driver
310 If the sub-device needs to notify its v4l2_device parent of an event, then
312 whether there is a ``notify()`` callback defined and returns ``-ENODEV`` if not.
315 V4L2 sub-device userspace API
316 -----------------------------
318 Bridge drivers traditionally expose one or multiple video nodes to userspace,
321 hardware from applications. For complex devices, finer-grained control of the
322 device than what the video nodes offer may be required. In those cases, bridge
326 Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
327 sub-devices directly. If a sub-device supports direct userspace configuration
330 After registering sub-devices, the :c:type:`v4l2_device` driver can create
331 device nodes for all registered sub-devices marked with
333 :c:func:`v4l2_device_register_subdev_nodes`. Those device nodes will be
334 automatically removed when sub-devices are unregistered.
348 controls implemented in the sub-device. Depending on the driver, those
350 nodes.
358 events generated by the sub-device. Depending on the driver, those
359 events can also be reported by one (or several) V4L2 device nodes.
361 Sub-device drivers that want to use events need to set the
363 the sub-device. After registration events can be queued as usual on the
371 All ioctls not in the above list are passed directly to the sub-device
374 Read-only sub-device userspace API
375 ----------------------------------
383 configuration through a read-only API, that does not permit applications to
391 through a read-only API.
393 To create a read-only device node for all the subdevices registered with the
398 sub-device device nodes registered with
405 These ioctls are only allowed on a read-only subdevice device node
406 for the :ref:`V4L2_SUBDEV_FORMAT_TRY <v4l2-subdev-format-whence>`
413 These ioctls are not allowed on a read-only subdevice node.
417 the errno variable is set to ``-EPERM``.
419 I2C sub-device drivers
420 ----------------------
423 ease the use of these drivers (``v4l2-common.h``).
433 .. code-block:: c
442 .. code-block:: c
444 v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
452 .. code-block:: c
462 .. code-block:: c
468 .. code-block:: c
474 when the ``remove()`` callback is called. This will unregister the sub-device
475 from the bridge driver. It is safe to call this even if the sub-device was
488 .. code-block:: c
500 are only used if the previous argument is 0. A non-zero argument means that you
528 -------------------------------------
542 device configuration, is stored in the sub-device itself as part of
547 Sub-device drivers can opt-in and use state to manage their active configuration
549 before registering the sub-device. They must also call v4l2_subdev_cleanup()
550 to release all the allocated resources before unregistering the sub-device.
555 V4L2 sub-device operations that use both the :ref:`ACTIVE and TRY formats
556 <v4l2-subdev-format-whence>` receive the correct state to operate on through
564 calling :c:func:`v4l2_subdev_lock_and_get_active_state()`. The sub-device active
589 .. code-block:: c
591 sd->ctrl_handler->lock = &priv->mutex;
592 sd->state_lock = &priv->mutex;
596 V4L2 sub-device functions and data structures
597 ---------------------------------------------
599 .. kernel-doc:: include/media/v4l2-subdev.h