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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:
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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.
158 run-time bridge-subdevice interaction is in both cases the same.
160 Registering synchronous sub-devices
170 After this function was called successfully the subdev->dev field points to
173 If the v4l2_device parent device has a non-NULL mdev field, the sub-device
176 You can unregister a sub-device using:
182 :c:type:`sd <v4l2_subdev>`->dev == ``NULL``.
184 .. _media-registering-async-subdevs:
186 Registering asynchronous sub-devices
193 the driver might decide to return ``-EPROBE_DEFER`` to request further reprobing
200 Drivers must complete all initialization of the sub-device before
202 enabling runtime PM. This is because the sub-device becomes accessible
205 Asynchronous sub-device notifiers
221 Async connection descriptors describe connections to external sub-devices the
223 or ancillary link may be created when the related sub-device becomes
224 available. There may be one or more async connections to a given sub-device but
226 connections are bound as matching async sub-devices are found, one by one.
228 Asynchronous sub-device notifier for sub-devices
231 A driver that registers an asynchronous sub-device may also register an
232 asynchronous notifier. This is called an asynchronous sub-device notifier and the
234 initialised using :c:func:`v4l2_async_subdev_nf_init` instead. A sub-device
236 a path via async sub-devices and notifiers to a notifier that is not an
237 asynchronous sub-device notifier.
239 Asynchronous sub-device registration helper for camera sensor drivers
245 firmware. The notifier for the sub-device is unregistered and cleaned up with
246 the async sub-device, using :c:func:`v4l2_async_unregister_subdev`.
248 Asynchronous sub-device notifier example
252 :c:type:`v4l2_async_connection` embedded in a driver-specific struct. The &struct
255 .. code-block:: c
274 Asynchronous sub-device notifier callbacks
283 Drivers can store any type of custom data in their driver-specific
301 .. code-block:: c
303 err = sd->ops->core->g_std(sd, &norm);
307 .. code-block:: c
311 The macro will do the right ``NULL`` pointer checks and returns ``-ENODEV``
312 if :c:type:`sd <v4l2_subdev>` is ``NULL``, ``-ENOIOCTLCMD`` if either
313 :c:type:`sd <v4l2_subdev>`->core or :c:type:`sd <v4l2_subdev>`->core->g_std is ``NULL``, or the act…
314 :c:type:`sd <v4l2_subdev>`->ops->core->g_std ops.
316 It is also possible to call all or a subset of the sub-devices:
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325 .. code-block:: c
329 Any error except ``-ENOIOCTLCMD`` will exit the loop with that error. If no
330 errors (except ``-ENOIOCTLCMD``) occurred, then 0 is returned.
333 called. If non-zero, then only those whose group ID match that value will
335 :c:type:`sd <v4l2_subdev>`->grp_id to whatever value it wants (it's 0 by
336 default). This value is owned by the bridge driver and the sub-device driver
347 If the sub-device needs to notify its v4l2_device parent of an event, then
349 whether there is a ``notify()`` callback defined and returns ``-ENODEV`` if not.
352 V4L2 sub-device userspace API
353 -----------------------------
358 hardware from applications. For complex devices, finer-grained control of the
363 Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
364 sub-devices directly. If a sub-device supports direct userspace configuration
367 After registering sub-devices, the :c:type:`v4l2_device` driver can create
368 device nodes for all registered sub-devices marked with
371 automatically removed when sub-devices are unregistered.
385 controls implemented in the sub-device. Depending on the driver, those
395 events generated by the sub-device. Depending on the driver, those
398 Sub-device drivers that want to use events need to set the
400 the sub-device. After registration events can be queued as usual on the
408 All ioctls not in the above list are passed directly to the sub-device
411 Read-only sub-device userspace API
412 ----------------------------------
420 configuration through a read-only API, that does not permit applications to
428 through a read-only API.
430 To create a read-only device node for all the subdevices registered with the
435 sub-device device nodes registered with
442 These ioctls are only allowed on a read-only subdevice device node
443 for the :ref:`V4L2_SUBDEV_FORMAT_TRY <v4l2-subdev-format-whence>`
450 These ioctls are not allowed on a read-only subdevice node.
454 the errno variable is set to ``-EPERM``.
456 I2C sub-device drivers
457 ----------------------
460 ease the use of these drivers (``v4l2-common.h``).
470 .. code-block:: c
479 .. code-block:: c
481 v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
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499 .. code-block:: c
505 .. code-block:: c
511 when the ``remove()`` callback is called. This will unregister the sub-device
512 from the bridge driver. It is safe to call this even if the sub-device was
525 .. code-block:: c
537 are only used if the previous argument is 0. A non-zero argument means that you
565 -------------------------------------
579 device configuration, is stored in the sub-device itself as part of
584 Sub-device drivers can opt-in and use state to manage their active configuration
586 before registering the sub-device. They must also call v4l2_subdev_cleanup()
587 to release all the allocated resources before unregistering the sub-device.
592 V4L2 sub-device operations that use both the :ref:`ACTIVE and TRY formats
593 <v4l2-subdev-format-whence>` receive the correct state to operate on through
601 calling :c:func:`v4l2_subdev_lock_and_get_active_state()`. The sub-device active
626 .. code-block:: c
628 sd->ctrl_handler->lock = &priv->mutex;
629 sd->state_lock = &priv->mutex;
634 ----------------------------------------------------
641 V4L2 sub-device functions and data structures
642 ---------------------------------------------
644 .. kernel-doc:: include/media/v4l2-subdev.h