Lines Matching +full:sub +full:- +full:node
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);
117 subdev device node (if any) is opened/closed.
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);
132 sub-devices. The driver is still responsible for validating the correctness
133 of the format configuration between sub-devices and video nodes.
161 run-time bridge-subdevice interaction is in both cases the same.
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:
183 :c:type:`sd <v4l2_subdev>`->dev == ``NULL``.
189 the driver might decide to return ``-EPROBE_DEFER`` to request further reprobing
231 .. code-block:: c
233 err = sd->ops->core->g_std(sd, &norm);
237 .. code-block:: c
241 The macro will do the right ``NULL`` pointer checks and returns ``-ENODEV``
242 if :c:type:`sd <v4l2_subdev>` is ``NULL``, ``-ENOIOCTLCMD`` if either
243 :c:type:`sd <v4l2_subdev>`->core or :c:type:`sd <v4l2_subdev>`->core->g_std is ``NULL``, or the act…
244 :c:type:`sd <v4l2_subdev>`->ops->core->g_std ops.
246 It is also possible to call all or a subset of the sub-devices:
248 .. code-block:: c
255 .. code-block:: c
259 Any error except ``-ENOIOCTLCMD`` will exit the loop with that error. If no
260 errors (except ``-ENOIOCTLCMD``) occurred, then 0 is returned.
263 called. If non-zero, then only those whose group ID match that value will
265 :c:type:`sd <v4l2_subdev>`->grp_id to whatever value it wants (it's 0 by
266 default). This value is owned by the bridge driver and the sub-device driver
277 If the sub-device needs to notify its v4l2_device parent of an event, then
279 whether there is a ``notify()`` callback defined and returns ``-ENODEV`` if not.
282 V4L2 sub-device userspace API
283 -----------------------------
287 response to video node operations. This hides the complexity of the underlying
288 hardware from applications. For complex devices, finer-grained control of the
293 Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
294 sub-devices directly. If a sub-device supports direct userspace configuration
297 After registering sub-devices, the :c:type:`v4l2_device` driver can create
298 device nodes for all registered sub-devices marked with
301 automatically removed when sub-devices are unregistered.
303 The device node handles a subset of the V4L2 API.
315 controls implemented in the sub-device. Depending on the driver, those
325 events generated by the sub-device. Depending on the driver, those
328 Sub-device drivers that want to use events need to set the
330 the sub-device. After registration events can be queued as usual on the
331 :c:type:`v4l2_subdev`.devnode device node.
338 All ioctls not in the above list are passed directly to the sub-device
341 Read-only sub-device userspace API
342 ----------------------------------
347 device node and thus do not usually register any.
350 configuration through a read-only API, that does not permit applications to
352 node to inspect them.
358 through a read-only API.
360 To create a read-only device node for all the subdevices registered with the
365 sub-device device nodes registered with
372 These ioctls are only allowed on a read-only subdevice device node
373 for the :ref:`V4L2_SUBDEV_FORMAT_TRY <v4l2-subdev-format-whence>`
380 These ioctls are not allowed on a read-only subdevice node.
384 the errno variable is set to ``-EPERM``.
386 I2C sub-device drivers
387 ----------------------
390 ease the use of these drivers (``v4l2-common.h``).
400 .. code-block:: c
409 .. code-block:: c
411 v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
419 .. code-block:: c
429 .. code-block:: c
435 .. code-block:: c
441 when the ``remove()`` callback is called. This will unregister the sub-device
442 from the bridge driver. It is safe to call this even if the sub-device was
455 .. code-block:: c
467 are only used if the previous argument is 0. A non-zero argument means that you
494 V4L2 sub-device functions and data structures
495 ---------------------------------------------
497 .. kernel-doc:: include/media/v4l2-subdev.h