Lines Matching +full:a +full:- +full:c
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
17 struct if more state information needs to be stored. Usually there is a
18 low-level device struct (e.g. ``i2c_client``) that contains the device data as
20 data of :c:type:`v4l2_subdev` using :c:func:`v4l2_set_subdevdata`. That makes
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`.
26 a :c:type:`v4l2_subdev` pointer, for other buses you may have to use other
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
32 :c:func:`v4l2_get_subdev_hostdata` and :c:func:`v4l2_set_subdev_hostdata`.
34 From the bridge driver perspective, you load the sub-device module and somehow
35 obtain the :c:type:`v4l2_subdev` pointer. For i2c devices this is easy: you call
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
42 do so many different things and you do not want to end up with a huge ops struct
43 of which only a handful of ops are commonly implemented, the function pointers
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:
92 :c:func:`v4l2_subdev_init <v4l2_subdev_init>`
93 (:c:type:`sd <v4l2_subdev>`, &\ :c:type:`ops <v4l2_subdev_ops>`).
96 Afterwards you need to initialize :c:type:`sd <v4l2_subdev>`->name with a
101 :c:type:`media_entity` struct embedded in the :c:type:`v4l2_subdev` struct
102 (entity field) by calling :c:func:`media_entity_pads_init`, if the entity has
105 .. code-block:: c
107 struct media_pad *pads = &my_sd->pads;
110 err = media_entity_pads_init(&sd->entity, npads, pads);
116 A reference to the entity will be automatically acquired/released when the
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
126 link_validate field in :c:type:`v4l2_subdev_pad_ops` to provide its own link
130 between sub-devices and video nodes.
133 :c:func:`v4l2_subdev_link_validate_default` is used instead. This function
151 asynchronously to bridge devices. An example of such a configuration is a Device
158 run-time bridge-subdevice interaction is in both cases the same.
160 In the **synchronous** case a device (bridge) driver needs to register the
161 :c:type:`v4l2_subdev` with the v4l2_device:
163 :c:func:`v4l2_device_register_subdev <v4l2_device_register_subdev>`
164 (:c:type:`v4l2_dev <v4l2_device>`, :c:type:`sd <v4l2_subdev>`).
167 After this function was called successfully the subdev->dev field points to
168 the :c:type:`v4l2_device`.
170 If the v4l2_device parent device has a non-NULL mdev field, the sub-device
173 You can unregister a sub-device using:
175 :c:func:`v4l2_device_unregister_subdev <v4l2_device_unregister_subdev>`
176 (:c:type:`sd <v4l2_subdev>`).
180 :c:type:`sd <v4l2_subdev>`->dev == ``NULL``.
184 all the requirements for a successful probing are satisfied. This can include a
185 check for a master clock availability. If any of the conditions aren't satisfied
186 the driver might decide to return ``-EPROBE_DEFER`` to request further reprobing
188 the :c:func:`v4l2_async_register_subdev` function. Unregistration is
189 performed using the :c:func:`v4l2_async_unregister_subdev` call. Subdevices
190 registered this way are stored in a global list of subdevices, ready to be
193 Bridge drivers in turn have to register a notifier object. This is
194 performed using the :c:func:`v4l2_async_notifier_register` call. To
196 :c:func:`v4l2_async_notifier_unregister`. The former of the two functions
197 takes two arguments: a pointer to struct :c:type:`v4l2_device` and a
198 pointer to struct :c:type:`v4l2_async_notifier`.
201 notifier must be initialized using the :c:func:`v4l2_async_notifier_init`.
202 Second, bridge drivers can then begin to form a list of subdevice descriptors
204 to add subdevice descriptors to a notifier, depending on the type of device and
207 :c:func:`v4l2_async_notifier_add_fwnode_remote_subdev` and
208 :c:func:`v4l2_async_notifier_add_i2c_subdev` are for bridge and ISP drivers for
209 registering their async sub-devices with the notifier.
211 :c:func:`v4l2_async_register_subdev_sensor` is a helper function for
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
219 :c:type:`v4l2_async_subdev` shall be the first member of this struct:
221 .. code-block:: c
241 registered subdevices to them. If a match is detected the ``.bound()``
243 .complete() callback is called. When a subdevice is removed from the
249 The advantage of using :c:type:`v4l2_subdev` is that it is a generic struct and
250 does not contain any knowledge about the underlying hardware. So a driver might
251 contain several subdevs that use an I2C bus, but also a subdev that is
258 .. code-block:: c
260 err = sd->ops->core->g_std(sd, &norm);
264 .. code-block:: c
268 The macro will do the right ``NULL`` pointer checks and returns ``-ENODEV``
269 if :c:type:`sd <v4l2_subdev>` is ``NULL``, ``-ENOIOCTLCMD`` if either
270 :c:type:`sd <v4l2_subdev>`->core or :c:type:`sd <v4l2_subdev>`->core->g_std is ``NULL``, or the act…
271 :c:type:`sd <v4l2_subdev>`->ops->core->g_std ops.
273 It is also possible to call all or a subset of the sub-devices:
275 .. code-block:: c
282 .. code-block:: c
286 Any error except ``-ENOIOCTLCMD`` will exit the loop with that error. If no
287 errors (except ``-ENOIOCTLCMD``) occurred, then 0 is returned.
289 The second argument to both calls is a group ID. If 0, then all subdevs are
290 called. If non-zero, then only those whose group ID match that value will
291 be called. Before a bridge driver registers a subdev it can set
292 :c:type:`sd <v4l2_subdev>`->grp_id to whatever value it wants (it's 0 by
293 default). This value is owned by the bridge driver and the sub-device driver
297 For example, there may be multiple audio chips on a board, each capable of
304 If the sub-device needs to notify its v4l2_device parent of an event, then
306 whether there is a ``notify()`` callback defined and returns ``-ENODEV`` if not.
309 V4L2 sub-device userspace API
310 -----------------------------
313 and control subdevices through the :c:type:`v4l2_subdev_ops` operations in
315 hardware from applications. For complex devices, finer-grained control of the
320 Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
321 sub-devices directly. If a sub-device supports direct userspace configuration
324 After registering sub-devices, the :c:type:`v4l2_device` driver can create
325 device nodes for all registered sub-devices marked with
327 :c:func:`v4l2_device_register_subdev_nodes`. Those device nodes will be
328 automatically removed when sub-devices are unregistered.
330 The device node handles a subset of the V4L2 API.
342 controls implemented in the sub-device. Depending on the driver, those
352 events generated by the sub-device. Depending on the driver, those
355 Sub-device drivers that want to use events need to set the
356 ``V4L2_SUBDEV_FL_HAS_EVENTS`` :c:type:`v4l2_subdev`.flags before registering
357 the sub-device. After registration events can be queued as usual on the
358 :c:type:`v4l2_subdev`.devnode device node.
365 All ioctls not in the above list are passed directly to the sub-device
368 Read-only sub-device userspace API
369 ----------------------------------
372 the kernel API realized by :c:type:`v4l2_subdev_ops` structure do not usually
377 configuration through a read-only API, that does not permit applications to
385 through a read-only API.
387 To create a read-only device node for all the subdevices registered with the
388 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` set, the :c:type:`v4l2_device` driver should call
389 :c:func:`v4l2_device_register_ro_subdev_nodes`.
392 sub-device device nodes registered with
393 :c:func:`v4l2_device_register_ro_subdev_nodes`.
399 These ioctls are only allowed on a read-only subdevice device node
400 for the :ref:`V4L2_SUBDEV_FORMAT_TRY <v4l2-subdev-format-whence>`
407 These ioctls are not allowed on a read-only subdevice node.
410 ``V4L2_SUBDEV_FORMAT_ACTIVE``, the core returns a negative error code and
411 the errno variable is set to ``-EPERM``.
413 I2C sub-device drivers
414 ----------------------
417 ease the use of these drivers (``v4l2-common.h``).
419 The recommended method of adding :c:type:`v4l2_subdev` support to an I2C driver
420 is to embed the :c:type:`v4l2_subdev` struct into the state struct that is
422 struct and in that case you can just create a :c:type:`v4l2_subdev` directly.
424 A typical state struct would look like this (where 'chipname' is replaced by
427 .. code-block:: c
434 Initialize the :c:type:`v4l2_subdev` struct as follows:
436 .. code-block:: c
438 v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
440 This function will fill in all the fields of :c:type:`v4l2_subdev` ensure that
441 the :c:type:`v4l2_subdev` and i2c_client both point to one another.
443 You should also add a helper inline function to go from a :c:type:`v4l2_subdev`
444 pointer to a chipname_state struct:
446 .. code-block:: c
453 Use this to go from the :c:type:`v4l2_subdev` struct to the ``i2c_client``
456 .. code-block:: c
460 And this to go from an ``i2c_client`` to a :c:type:`v4l2_subdev` struct:
462 .. code-block:: c
467 :c:func:`v4l2_device_unregister_subdev`\ (:c:type:`sd <v4l2_subdev>`)
468 when the ``remove()`` callback is called. This will unregister the sub-device
469 from the bridge driver. It is safe to call this even if the sub-device was
476 :c:func:`v4l2_device_unregister_subdev`\ (:c:type:`sd <v4l2_subdev>`)
482 .. code-block:: c
488 and calls :c:func:`i2c_new_client_device` with the given ``i2c_adapter`` and
492 You can also use the last argument of :c:func:`v4l2_i2c_new_subdev` to pass
494 are only used if the previous argument is 0. A non-zero argument means that you
499 Note that the chipid you pass to :c:func:`v4l2_i2c_new_subdev` is usually
500 the same as the module name. It allows you to specify a chip variant, e.g.
502 The use of chipid is something that needs to be looked at more closely at a
509 :c:func:`v4l2_i2c_new_subdev_board` uses an :c:type:`i2c_board_info` struct
516 The :c:func:`v4l2_i2c_new_subdev` function will call
517 :c:func:`v4l2_i2c_new_subdev_board`, internally filling a
518 :c:type:`i2c_board_info` structure using the ``client_type`` and the
521 V4L2 sub-device functions and data structures
522 ---------------------------------------------
524 .. kernel-doc:: include/media/v4l2-subdev.h