1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
3 V4L2 sub-devices 3 V4L2 sub-devices
4 ---------------- 4 ----------------
5 5
6 Many drivers need to communicate with sub-devi 6 Many drivers need to communicate with sub-devices. These devices can do all
7 sort of tasks, but most commonly they handle a 7 sort of tasks, but most commonly they handle audio and/or video muxing,
8 encoding or decoding. For webcams common sub-d 8 encoding or decoding. For webcams common sub-devices are sensors and camera
9 controllers. 9 controllers.
10 10
11 Usually these are I2C devices, but not necessa 11 Usually these are I2C devices, but not necessarily. In order to provide the
12 driver with a consistent interface to these su 12 driver with a consistent interface to these sub-devices the
13 :c:type:`v4l2_subdev` struct (v4l2-subdev.h) w 13 :c:type:`v4l2_subdev` struct (v4l2-subdev.h) was created.
14 14
15 Each sub-device driver must have a :c:type:`v4 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 i 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 s 17 struct if more state information needs to be stored. Usually there is a
18 low-level device struct (e.g. ``i2c_client``) 18 low-level device struct (e.g. ``i2c_client``) that contains the device data as
19 setup by the kernel. It is recommended to stor 19 setup by the kernel. It is recommended to store that pointer in the private
20 data of :c:type:`v4l2_subdev` using :c:func:`v 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 21 it easy to go from a :c:type:`v4l2_subdev` to the actual low-level bus-specific
22 device data. 22 device data.
23 23
24 You also need a way to go from the low-level s 24 You also need a way to go from the low-level struct to :c:type:`v4l2_subdev`.
25 For the common i2c_client struct the i2c_set_c 25 For the common i2c_client struct the i2c_set_clientdata() call is used to store
26 a :c:type:`v4l2_subdev` pointer, for other bus 26 a :c:type:`v4l2_subdev` pointer, for other buses you may have to use other
27 methods. 27 methods.
28 28
29 Bridges might also need to store per-subdev pr 29 Bridges might also need to store per-subdev private data, such as a pointer to
30 bridge-specific per-subdev private data. The : 30 bridge-specific per-subdev private data. The :c:type:`v4l2_subdev` structure
31 provides host private data for that purpose th 31 provides host private data for that purpose that can be accessed with
32 :c:func:`v4l2_get_subdev_hostdata` and :c:func 32 :c:func:`v4l2_get_subdev_hostdata` and :c:func:`v4l2_set_subdev_hostdata`.
33 33
34 From the bridge driver perspective, you load t 34 From the bridge driver perspective, you load the sub-device module and somehow
35 obtain the :c:type:`v4l2_subdev` pointer. For 35 obtain the :c:type:`v4l2_subdev` pointer. For i2c devices this is easy: you call
36 ``i2c_get_clientdata()``. For other buses some 36 ``i2c_get_clientdata()``. For other buses something similar needs to be done.
37 Helper functions exist for sub-devices on an I !! 37 Helper functions exists for sub-devices on an I2C bus that do most of this
38 tricky work for you. 38 tricky work for you.
39 39
40 Each :c:type:`v4l2_subdev` contains function p 40 Each :c:type:`v4l2_subdev` contains function pointers that sub-device drivers
41 can implement (or leave ``NULL`` if it is not 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 wan 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 im 43 of which only a handful of ops are commonly implemented, the function pointers
44 are sorted according to category and each cate 44 are sorted according to category and each category has its own ops struct.
45 45
46 The top-level ops struct contains pointers to 46 The top-level ops struct contains pointers to the category ops structs, which
47 may be NULL if the subdev driver does not supp 47 may be NULL if the subdev driver does not support anything from that category.
48 48
49 It looks like this: 49 It looks like this:
50 50
51 .. code-block:: c 51 .. code-block:: c
52 52
53 struct v4l2_subdev_core_ops { 53 struct v4l2_subdev_core_ops {
54 int (*log_status)(struct v4l2_ 54 int (*log_status)(struct v4l2_subdev *sd);
55 int (*init)(struct v4l2_subdev 55 int (*init)(struct v4l2_subdev *sd, u32 val);
56 ... 56 ...
57 }; 57 };
58 58
59 struct v4l2_subdev_tuner_ops { 59 struct v4l2_subdev_tuner_ops {
60 ... 60 ...
61 }; 61 };
62 62
63 struct v4l2_subdev_audio_ops { 63 struct v4l2_subdev_audio_ops {
64 ... 64 ...
65 }; 65 };
66 66
67 struct v4l2_subdev_video_ops { 67 struct v4l2_subdev_video_ops {
68 ... 68 ...
69 }; 69 };
70 70
71 struct v4l2_subdev_pad_ops { 71 struct v4l2_subdev_pad_ops {
72 ... 72 ...
73 }; 73 };
74 74
75 struct v4l2_subdev_ops { 75 struct v4l2_subdev_ops {
76 const struct v4l2_subdev_core_ 76 const struct v4l2_subdev_core_ops *core;
77 const struct v4l2_subdev_tuner 77 const struct v4l2_subdev_tuner_ops *tuner;
78 const struct v4l2_subdev_audio 78 const struct v4l2_subdev_audio_ops *audio;
79 const struct v4l2_subdev_video 79 const struct v4l2_subdev_video_ops *video;
80 const struct v4l2_subdev_pad_o 80 const struct v4l2_subdev_pad_ops *video;
81 }; 81 };
82 82
83 The core ops are common to all subdevs, the ot 83 The core ops are common to all subdevs, the other categories are implemented
84 depending on the sub-device. E.g. a video devi 84 depending on the sub-device. E.g. a video device is unlikely to support the
85 audio ops and vice versa. 85 audio ops and vice versa.
86 86
87 This setup limits the number of function point 87 This setup limits the number of function pointers while still making it easy
88 to add new ops and categories. 88 to add new ops and categories.
89 89
90 A sub-device driver initializes the :c:type:`v 90 A sub-device driver initializes the :c:type:`v4l2_subdev` struct using:
91 91
92 :c:func:`v4l2_subdev_init <v4l2_subdev 92 :c:func:`v4l2_subdev_init <v4l2_subdev_init>`
93 (:c:type:`sd <v4l2_subdev>`, &\ :c:typ 93 (:c:type:`sd <v4l2_subdev>`, &\ :c:type:`ops <v4l2_subdev_ops>`).
94 94
95 95
96 Afterwards you need to initialize :c:type:`sd 96 Afterwards you need to initialize :c:type:`sd <v4l2_subdev>`->name with a
97 unique name and set the module owner. This is 97 unique name and set the module owner. This is done for you if you use the
98 i2c helper functions. 98 i2c helper functions.
99 99
100 If integration with the media framework is nee 100 If integration with the media framework is needed, you must initialize the
101 :c:type:`media_entity` struct embedded in the 101 :c:type:`media_entity` struct embedded in the :c:type:`v4l2_subdev` struct
102 (entity field) by calling :c:func:`media_entit 102 (entity field) by calling :c:func:`media_entity_pads_init`, if the entity has
103 pads: 103 pads:
104 104
105 .. code-block:: c 105 .. code-block:: c
106 106
107 struct media_pad *pads = &my_sd->pads; 107 struct media_pad *pads = &my_sd->pads;
108 int err; 108 int err;
109 109
110 err = media_entity_pads_init(&sd->enti 110 err = media_entity_pads_init(&sd->entity, npads, pads);
111 111
112 The pads array must have been previously initi 112 The pads array must have been previously initialized. There is no need to
113 manually set the struct media_entity function !! 113 manually set the struct :c:type:`media_entity` function and name fields, but the
114 revision field must be initialized if needed. 114 revision field must be initialized if needed.
115 115
116 A reference to the entity will be automaticall 116 A reference to the entity will be automatically acquired/released when the
117 subdev device node (if any) is opened/closed. 117 subdev device node (if any) is opened/closed.
118 118
119 Don't forget to cleanup the media entity befor 119 Don't forget to cleanup the media entity before the sub-device is destroyed:
120 120
121 .. code-block:: c 121 .. code-block:: c
122 122
123 media_entity_cleanup(&sd->entity); 123 media_entity_cleanup(&sd->entity);
124 124
125 If a sub-device driver implements sink pads, t !! 125 If the subdev driver intends to process video and integrate with the media
126 link_validate field in :c:type:`v4l2_subdev_pa !! 126 framework, it must implement format related functionality using
127 validation function. For every link in the pip !! 127 :c:type:`v4l2_subdev_pad_ops` instead of :c:type:`v4l2_subdev_video_ops`.
128 operation of the sink end of the link is calle !! 128
129 still responsible for validating the correctne !! 129 In that case, the subdev driver may set the link_validate field to provide
130 between sub-devices and video nodes. !! 130 its own link validation function. The link validation function is called for
>> 131 every link in the pipeline where both of the ends of the links are V4L2
>> 132 sub-devices. The driver is still responsible for validating the correctness
>> 133 of the format configuration between sub-devices and video nodes.
131 134
132 If link_validate op is not set, the default fu 135 If link_validate op is not set, the default function
133 :c:func:`v4l2_subdev_link_validate_default` is 136 :c:func:`v4l2_subdev_link_validate_default` is used instead. This function
134 ensures that width, height and the media bus p 137 ensures that width, height and the media bus pixel code are equal on both source
135 and sink of the link. Subdev drivers are also 138 and sink of the link. Subdev drivers are also free to use this function to
136 perform the checks mentioned above in addition 139 perform the checks mentioned above in addition to their own checks.
137 140
138 Subdev registration <<
139 ~~~~~~~~~~~~~~~~~~~ <<
140 <<
141 There are currently two ways to register subde 141 There are currently two ways to register subdevices with the V4L2 core. The
142 first (traditional) possibility is to have sub 142 first (traditional) possibility is to have subdevices registered by bridge
143 drivers. This can be done when the bridge driv 143 drivers. This can be done when the bridge driver has the complete information
144 about subdevices connected to it and knows exa 144 about subdevices connected to it and knows exactly when to register them. This
145 is typically the case for internal subdevices, 145 is typically the case for internal subdevices, like video data processing units
146 within SoCs or complex PCI(e) boards, camera s 146 within SoCs or complex PCI(e) boards, camera sensors in USB cameras or connected
147 to SoCs, which pass information about them to 147 to SoCs, which pass information about them to bridge drivers, usually in their
148 platform data. 148 platform data.
149 149
150 There are however also situations where subdev 150 There are however also situations where subdevices have to be registered
151 asynchronously to bridge devices. An example o 151 asynchronously to bridge devices. An example of such a configuration is a Device
152 Tree based system where information about subd 152 Tree based system where information about subdevices is made available to the
153 system independently from the bridge devices, 153 system independently from the bridge devices, e.g. when subdevices are defined
154 in DT as I2C device nodes. The API used in thi 154 in DT as I2C device nodes. The API used in this second case is described further
155 below. 155 below.
156 156
157 Using one or the other registration method onl 157 Using one or the other registration method only affects the probing process, the
158 run-time bridge-subdevice interaction is in bo 158 run-time bridge-subdevice interaction is in both cases the same.
159 159
160 Registering synchronous sub-devices !! 160 In the synchronous case a device (bridge) driver needs to register the
161 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
162 <<
163 In the **synchronous** case a device (bridge) <<
164 :c:type:`v4l2_subdev` with the v4l2_device: 161 :c:type:`v4l2_subdev` with the v4l2_device:
165 162
166 :c:func:`v4l2_device_register_subdev < 163 :c:func:`v4l2_device_register_subdev <v4l2_device_register_subdev>`
167 (:c:type:`v4l2_dev <v4l2_device>`, :c: 164 (:c:type:`v4l2_dev <v4l2_device>`, :c:type:`sd <v4l2_subdev>`).
168 165
169 This can fail if the subdev module disappeared 166 This can fail if the subdev module disappeared before it could be registered.
170 After this function was called successfully th 167 After this function was called successfully the subdev->dev field points to
171 the :c:type:`v4l2_device`. 168 the :c:type:`v4l2_device`.
172 169
173 If the v4l2_device parent device has a non-NUL 170 If the v4l2_device parent device has a non-NULL mdev field, the sub-device
174 entity will be automatically registered with t 171 entity will be automatically registered with the media device.
175 172
176 You can unregister a sub-device using: 173 You can unregister a sub-device using:
177 174
178 :c:func:`v4l2_device_unregister_subdev 175 :c:func:`v4l2_device_unregister_subdev <v4l2_device_unregister_subdev>`
179 (:c:type:`sd <v4l2_subdev>`). 176 (:c:type:`sd <v4l2_subdev>`).
180 177
>> 178
181 Afterwards the subdev module can be unloaded a 179 Afterwards the subdev module can be unloaded and
182 :c:type:`sd <v4l2_subdev>`->dev == ``NULL``. 180 :c:type:`sd <v4l2_subdev>`->dev == ``NULL``.
183 181
184 .. _media-registering-async-subdevs: !! 182 You can call an ops function either directly:
185 <<
186 Registering asynchronous sub-devices <<
187 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
188 <<
189 In the **asynchronous** case subdevice probing <<
190 the bridge driver availability. The subdevice <<
191 all the requirements for a successful probing <<
192 check for a master clock availability. If any <<
193 the driver might decide to return ``-EPROBE_DE <<
194 attempts. Once all conditions are met the subd <<
195 the :c:func:`v4l2_async_register_subdev` funct <<
196 performed using the :c:func:`v4l2_async_unregi <<
197 registered this way are stored in a global lis <<
198 picked up by bridge drivers. <<
199 <<
200 Drivers must complete all initialization of th <<
201 registering it using :c:func:`v4l2_async_regis <<
202 enabling runtime PM. This is because the sub-d <<
203 as soon as it gets registered. <<
204 <<
205 Asynchronous sub-device notifiers <<
206 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
207 <<
208 Bridge drivers in turn have to register a noti <<
209 using the :c:func:`v4l2_async_nf_register` cal <<
210 driver has to call :c:func:`v4l2_async_nf_unre <<
211 of an unregister notifier, it must be cleaned <<
212 :c:func:`v4l2_async_nf_cleanup`. <<
213 <<
214 Before registering the notifier, bridge driver <<
215 notifier must be initialized using the :c:func <<
216 bridge drivers can then begin to form a list o <<
217 that the bridge device needs for its <<
218 operation. :c:func:`v4l2_async_nf_add_fwnode`, <<
219 :c:func:`v4l2_async_nf_add_fwnode_remote` and <<
220 <<
221 Async connection descriptors describe connecti <<
222 drivers for which are not yet probed. Based on <<
223 or ancillary link may be created when the rela <<
224 available. There may be one or more async conn <<
225 this is not known at the time of adding the co <<
226 connections are bound as matching async sub-de <<
227 <<
228 Asynchronous sub-device notifier for sub-devic <<
229 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
230 <<
231 A driver that registers an asynchronous sub-de <<
232 asynchronous notifier. This is called an async <<
233 process is similar to that of a bridge driver <<
234 initialised using :c:func:`v4l2_async_subdev_n <<
235 notifier may complete only after the V4L2 devi <<
236 a path via async sub-devices and notifiers to <<
237 asynchronous sub-device notifier. <<
238 <<
239 Asynchronous sub-device registration helper fo <<
240 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
241 <<
242 :c:func:`v4l2_async_register_subdev_sensor` is <<
243 drivers registering their own async connection <<
244 and further registers async connections for le <<
245 firmware. The notifier for the sub-device is u <<
246 the async sub-device, using :c:func:`v4l2_asyn <<
247 <<
248 Asynchronous sub-device notifier example <<
249 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
250 <<
251 These functions allocate an async connection d <<
252 :c:type:`v4l2_async_connection` embedded in a <<
253 :c:type:`v4l2_async_connection` shall be the f <<
254 <<
255 .. code-block:: c <<
256 <<
257 struct my_async_connection { <<
258 struct v4l2_async_connection a <<
259 ... <<
260 }; <<
261 <<
262 struct my_async_connection *my_asc; <<
263 struct fwnode_handle *ep; <<
264 <<
265 ... <<
266 <<
267 my_asc = v4l2_async_nf_add_fwnode_remo <<
268 <<
269 fwnode_handle_put(ep); <<
270 <<
271 if (IS_ERR(my_asc)) <<
272 return PTR_ERR(my_asc); <<
273 <<
274 Asynchronous sub-device notifier callbacks <<
275 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
276 <<
277 The V4L2 core will then use these connection d <<
278 registered subdevices to them. If a match is d <<
279 callback is called. After all connections have <<
280 callback is called. When a connection is remov <<
281 ``.unbind()`` method is called. All three call <<
282 <<
283 Drivers can store any type of custom data in t <<
284 :c:type:`v4l2_async_connection` wrapper. If an <<
285 handling when the structure is freed, drivers <<
286 notifier callback. The framework will call it <<
287 :c:type:`v4l2_async_connection`. <<
288 <<
289 Calling subdev operations <<
290 ~~~~~~~~~~~~~~~~~~~~~~~~~ <<
291 <<
292 The advantage of using :c:type:`v4l2_subdev` i <<
293 does not contain any knowledge about the under <<
294 contain several subdevs that use an I2C bus, b <<
295 controlled through GPIO pins. This distinction <<
296 up the device, but once the subdev is register <<
297 <<
298 Once the subdev has been registered you can ca <<
299 directly: <<
300 183
301 .. code-block:: c 184 .. code-block:: c
302 185
303 err = sd->ops->core->g_std(sd, &norm); 186 err = sd->ops->core->g_std(sd, &norm);
304 187
305 but it is better and easier to use this macro: 188 but it is better and easier to use this macro:
306 189
307 .. code-block:: c 190 .. code-block:: c
308 191
309 err = v4l2_subdev_call(sd, core, g_std 192 err = v4l2_subdev_call(sd, core, g_std, &norm);
310 193
311 The macro will do the right ``NULL`` pointer c !! 194 The macro will to the right ``NULL`` pointer checks and returns ``-ENODEV``
312 if :c:type:`sd <v4l2_subdev>` is ``NULL``, ``- 195 if :c:type:`sd <v4l2_subdev>` is ``NULL``, ``-ENOIOCTLCMD`` if either
313 :c:type:`sd <v4l2_subdev>`->core or :c:type:`s 196 :c:type:`sd <v4l2_subdev>`->core or :c:type:`sd <v4l2_subdev>`->core->g_std is ``NULL``, or the actual result of the
314 :c:type:`sd <v4l2_subdev>`->ops->core->g_std o 197 :c:type:`sd <v4l2_subdev>`->ops->core->g_std ops.
315 198
316 It is also possible to call all or a subset of 199 It is also possible to call all or a subset of the sub-devices:
317 200
318 .. code-block:: c 201 .. code-block:: c
319 202
320 v4l2_device_call_all(v4l2_dev, 0, core 203 v4l2_device_call_all(v4l2_dev, 0, core, g_std, &norm);
321 204
322 Any subdev that does not support this ops is s 205 Any subdev that does not support this ops is skipped and error results are
323 ignored. If you want to check for errors use t 206 ignored. If you want to check for errors use this:
324 207
325 .. code-block:: c 208 .. code-block:: c
326 209
327 err = v4l2_device_call_until_err(v4l2_ 210 err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_std, &norm);
328 211
329 Any error except ``-ENOIOCTLCMD`` will exit th 212 Any error except ``-ENOIOCTLCMD`` will exit the loop with that error. If no
330 errors (except ``-ENOIOCTLCMD``) occurred, the 213 errors (except ``-ENOIOCTLCMD``) occurred, then 0 is returned.
331 214
332 The second argument to both calls is a group I 215 The second argument to both calls is a group ID. If 0, then all subdevs are
333 called. If non-zero, then only those whose gro 216 called. If non-zero, then only those whose group ID match that value will
334 be called. Before a bridge driver registers a 217 be called. Before a bridge driver registers a subdev it can set
335 :c:type:`sd <v4l2_subdev>`->grp_id to whatever 218 :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 dr 219 default). This value is owned by the bridge driver and the sub-device driver
337 will never modify or use it. 220 will never modify or use it.
338 221
339 The group ID gives the bridge driver more cont 222 The group ID gives the bridge driver more control how callbacks are called.
340 For example, there may be multiple audio chips 223 For example, there may be multiple audio chips on a board, each capable of
341 changing the volume. But usually only one will 224 changing the volume. But usually only one will actually be used when the
342 user want to change the volume. You can set th 225 user want to change the volume. You can set the group ID for that subdev to
343 e.g. AUDIO_CONTROLLER and specify that as the 226 e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling
344 ``v4l2_device_call_all()``. That ensures that 227 ``v4l2_device_call_all()``. That ensures that it will only go to the subdev
345 that needs it. 228 that needs it.
346 229
347 If the sub-device needs to notify its v4l2_dev 230 If the sub-device needs to notify its v4l2_device parent of an event, then
348 it can call ``v4l2_subdev_notify(sd, notificat 231 it can call ``v4l2_subdev_notify(sd, notification, arg)``. This macro checks
349 whether there is a ``notify()`` callback defin 232 whether there is a ``notify()`` callback defined and returns ``-ENODEV`` if not.
350 Otherwise the result of the ``notify()`` call 233 Otherwise the result of the ``notify()`` call is returned.
351 234
>> 235 The advantage of using :c:type:`v4l2_subdev` is that it is a generic struct and
>> 236 does not contain any knowledge about the underlying hardware. So a driver might
>> 237 contain several subdevs that use an I2C bus, but also a subdev that is
>> 238 controlled through GPIO pins. This distinction is only relevant when setting
>> 239 up the device, but once the subdev is registered it is completely transparent.
>> 240
>> 241 In the asynchronous case subdevice probing can be invoked independently of the
>> 242 bridge driver availability. The subdevice driver then has to verify whether all
>> 243 the requirements for a successful probing are satisfied. This can include a
>> 244 check for a master clock availability. If any of the conditions aren't satisfied
>> 245 the driver might decide to return ``-EPROBE_DEFER`` to request further reprobing
>> 246 attempts. Once all conditions are met the subdevice shall be registered using
>> 247 the :c:func:`v4l2_async_register_subdev` function. Unregistration is
>> 248 performed using the :c:func:`v4l2_async_unregister_subdev` call. Subdevices
>> 249 registered this way are stored in a global list of subdevices, ready to be
>> 250 picked up by bridge drivers.
>> 251
>> 252 Bridge drivers in turn have to register a notifier object. This is
>> 253 performed using the :c:func:`v4l2_async_notifier_register` call. To
>> 254 unregister the notifier the driver has to call
>> 255 :c:func:`v4l2_async_notifier_unregister`. The former of the two functions
>> 256 takes two arguments: a pointer to struct :c:type:`v4l2_device` and a
>> 257 pointer to struct :c:type:`v4l2_async_notifier`.
>> 258
>> 259 Before registering the notifier, bridge drivers must do two things:
>> 260 first, the notifier must be initialized using the
>> 261 :c:func:`v4l2_async_notifier_init`. Second, bridge drivers can then
>> 262 begin to form a list of subdevice descriptors that the bridge device
>> 263 needs for its operation. Subdevice descriptors are added to the notifier
>> 264 using the :c:func:`v4l2_async_notifier_add_subdev` call. This function
>> 265 takes two arguments: a pointer to struct :c:type:`v4l2_async_notifier`,
>> 266 and a pointer to the subdevice descripter, which is of type struct
>> 267 :c:type:`v4l2_async_subdev`.
>> 268
>> 269 The V4L2 core will then use these descriptors to match asynchronously
>> 270 registered subdevices to them. If a match is detected the ``.bound()``
>> 271 notifier callback is called. After all subdevices have been located the
>> 272 .complete() callback is called. When a subdevice is removed from the
>> 273 system the .unbind() method is called. All three callbacks are optional.
>> 274
352 V4L2 sub-device userspace API 275 V4L2 sub-device userspace API
353 ----------------------------- 276 -----------------------------
354 277
355 Bridge drivers traditionally expose one or mul 278 Bridge drivers traditionally expose one or multiple video nodes to userspace,
356 and control subdevices through the :c:type:`v4 279 and control subdevices through the :c:type:`v4l2_subdev_ops` operations in
357 response to video node operations. This hides 280 response to video node operations. This hides the complexity of the underlying
358 hardware from applications. For complex device 281 hardware from applications. For complex devices, finer-grained control of the
359 device than what the video nodes offer may be 282 device than what the video nodes offer may be required. In those cases, bridge
360 drivers that implement :ref:`the media control 283 drivers that implement :ref:`the media controller API <media_controller>` may
361 opt for making the subdevice operations direct !! 284 opt for making the subdevice operations directly accessible from userpace.
362 285
363 Device nodes named ``v4l-subdev``\ *X* can be 286 Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
364 sub-devices directly. If a sub-device supports 287 sub-devices directly. If a sub-device supports direct userspace configuration
365 it must set the ``V4L2_SUBDEV_FL_HAS_DEVNODE`` 288 it must set the ``V4L2_SUBDEV_FL_HAS_DEVNODE`` flag before being registered.
366 289
367 After registering sub-devices, the :c:type:`v4 290 After registering sub-devices, the :c:type:`v4l2_device` driver can create
368 device nodes for all registered sub-devices ma 291 device nodes for all registered sub-devices marked with
369 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` by calling 292 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` by calling
370 :c:func:`v4l2_device_register_subdev_nodes`. T 293 :c:func:`v4l2_device_register_subdev_nodes`. Those device nodes will be
371 automatically removed when sub-devices are unr 294 automatically removed when sub-devices are unregistered.
372 295
373 The device node handles a subset of the V4L2 A 296 The device node handles a subset of the V4L2 API.
374 297
375 ``VIDIOC_QUERYCTRL``, 298 ``VIDIOC_QUERYCTRL``,
376 ``VIDIOC_QUERYMENU``, 299 ``VIDIOC_QUERYMENU``,
377 ``VIDIOC_G_CTRL``, 300 ``VIDIOC_G_CTRL``,
378 ``VIDIOC_S_CTRL``, 301 ``VIDIOC_S_CTRL``,
379 ``VIDIOC_G_EXT_CTRLS``, 302 ``VIDIOC_G_EXT_CTRLS``,
380 ``VIDIOC_S_EXT_CTRLS`` and 303 ``VIDIOC_S_EXT_CTRLS`` and
381 ``VIDIOC_TRY_EXT_CTRLS``: 304 ``VIDIOC_TRY_EXT_CTRLS``:
382 305
383 The controls ioctls are identical to t 306 The controls ioctls are identical to the ones defined in V4L2. They
384 behave identically, with the only exce 307 behave identically, with the only exception that they deal only with
385 controls implemented in the sub-device 308 controls implemented in the sub-device. Depending on the driver, those
386 controls can be also be accessed throu 309 controls can be also be accessed through one (or several) V4L2 device
387 nodes. 310 nodes.
388 311
389 ``VIDIOC_DQEVENT``, 312 ``VIDIOC_DQEVENT``,
390 ``VIDIOC_SUBSCRIBE_EVENT`` and 313 ``VIDIOC_SUBSCRIBE_EVENT`` and
391 ``VIDIOC_UNSUBSCRIBE_EVENT`` 314 ``VIDIOC_UNSUBSCRIBE_EVENT``
392 315
393 The events ioctls are identical to the 316 The events ioctls are identical to the ones defined in V4L2. They
394 behave identically, with the only exce 317 behave identically, with the only exception that they deal only with
395 events generated by the sub-device. De 318 events generated by the sub-device. Depending on the driver, those
396 events can also be reported by one (or 319 events can also be reported by one (or several) V4L2 device nodes.
397 320
398 Sub-device drivers that want to use ev 321 Sub-device drivers that want to use events need to set the
399 ``V4L2_SUBDEV_FL_HAS_EVENTS`` :c:type: 322 ``V4L2_SUBDEV_FL_HAS_EVENTS`` :c:type:`v4l2_subdev`.flags before registering
400 the sub-device. After registration eve 323 the sub-device. After registration events can be queued as usual on the
401 :c:type:`v4l2_subdev`.devnode device n 324 :c:type:`v4l2_subdev`.devnode device node.
402 325
403 To properly support events, the ``poll 326 To properly support events, the ``poll()`` file operation is also
404 implemented. 327 implemented.
405 328
406 Private ioctls 329 Private ioctls
407 330
408 All ioctls not in the above list are p 331 All ioctls not in the above list are passed directly to the sub-device
409 driver through the core::ioctl operati 332 driver through the core::ioctl operation.
410 333
411 Read-only sub-device userspace API 334 Read-only sub-device userspace API
412 ---------------------------------- 335 ----------------------------------
413 336
414 Bridge drivers that control their connected su 337 Bridge drivers that control their connected subdevices through direct calls to
415 the kernel API realized by :c:type:`v4l2_subde 338 the kernel API realized by :c:type:`v4l2_subdev_ops` structure do not usually
416 want userspace to be able to change the same p 339 want userspace to be able to change the same parameters through the subdevice
417 device node and thus do not usually register a 340 device node and thus do not usually register any.
418 341
419 It is sometimes useful to report to userspace 342 It is sometimes useful to report to userspace the current subdevice
420 configuration through a read-only API, that do 343 configuration through a read-only API, that does not permit applications to
421 change to the device parameters but allows int 344 change to the device parameters but allows interfacing to the subdevice device
422 node to inspect them. 345 node to inspect them.
423 346
424 For instance, to implement cameras based on co 347 For instance, to implement cameras based on computational photography, userspace
425 needs to know the detailed camera sensor confi 348 needs to know the detailed camera sensor configuration (in terms of skipping,
426 binning, cropping and scaling) for each suppor 349 binning, cropping and scaling) for each supported output resolution. To support
427 such use cases, bridge drivers may expose the 350 such use cases, bridge drivers may expose the subdevice operations to userspace
428 through a read-only API. 351 through a read-only API.
429 352
430 To create a read-only device node for all the 353 To create a read-only device node for all the subdevices registered with the
431 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` set, the :c:typ 354 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` set, the :c:type:`v4l2_device` driver should call
432 :c:func:`v4l2_device_register_ro_subdev_nodes` 355 :c:func:`v4l2_device_register_ro_subdev_nodes`.
433 356
434 Access to the following ioctls for userspace a 357 Access to the following ioctls for userspace applications is restricted on
435 sub-device device nodes registered with 358 sub-device device nodes registered with
436 :c:func:`v4l2_device_register_ro_subdev_nodes` 359 :c:func:`v4l2_device_register_ro_subdev_nodes`.
437 360
438 ``VIDIOC_SUBDEV_S_FMT``, 361 ``VIDIOC_SUBDEV_S_FMT``,
439 ``VIDIOC_SUBDEV_S_CROP``, 362 ``VIDIOC_SUBDEV_S_CROP``,
440 ``VIDIOC_SUBDEV_S_SELECTION``: 363 ``VIDIOC_SUBDEV_S_SELECTION``:
441 364
442 These ioctls are only allowed on a rea 365 These ioctls are only allowed on a read-only subdevice device node
443 for the :ref:`V4L2_SUBDEV_FORMAT_TRY < 366 for the :ref:`V4L2_SUBDEV_FORMAT_TRY <v4l2-subdev-format-whence>`
444 formats and selection rectangles. 367 formats and selection rectangles.
445 368
446 ``VIDIOC_SUBDEV_S_FRAME_INTERVAL``, 369 ``VIDIOC_SUBDEV_S_FRAME_INTERVAL``,
447 ``VIDIOC_SUBDEV_S_DV_TIMINGS``, 370 ``VIDIOC_SUBDEV_S_DV_TIMINGS``,
448 ``VIDIOC_SUBDEV_S_STD``: 371 ``VIDIOC_SUBDEV_S_STD``:
449 372
450 These ioctls are not allowed on a read 373 These ioctls are not allowed on a read-only subdevice node.
451 374
452 In case the ioctl is not allowed, or the forma 375 In case the ioctl is not allowed, or the format to modify is set to
453 ``V4L2_SUBDEV_FORMAT_ACTIVE``, the core return 376 ``V4L2_SUBDEV_FORMAT_ACTIVE``, the core returns a negative error code and
454 the errno variable is set to ``-EPERM``. 377 the errno variable is set to ``-EPERM``.
455 378
456 I2C sub-device drivers 379 I2C sub-device drivers
457 ---------------------- 380 ----------------------
458 381
459 Since these drivers are so common, special hel 382 Since these drivers are so common, special helper functions are available to
460 ease the use of these drivers (``v4l2-common.h 383 ease the use of these drivers (``v4l2-common.h``).
461 384
462 The recommended method of adding :c:type:`v4l2 385 The recommended method of adding :c:type:`v4l2_subdev` support to an I2C driver
463 is to embed the :c:type:`v4l2_subdev` struct i 386 is to embed the :c:type:`v4l2_subdev` struct into the state struct that is
464 created for each I2C device instance. Very sim 387 created for each I2C device instance. Very simple devices have no state
465 struct and in that case you can just create a 388 struct and in that case you can just create a :c:type:`v4l2_subdev` directly.
466 389
467 A typical state struct would look like this (w 390 A typical state struct would look like this (where 'chipname' is replaced by
468 the name of the chip): 391 the name of the chip):
469 392
470 .. code-block:: c 393 .. code-block:: c
471 394
472 struct chipname_state { 395 struct chipname_state {
473 struct v4l2_subdev sd; 396 struct v4l2_subdev sd;
474 ... /* additional state field 397 ... /* additional state fields */
475 }; 398 };
476 399
477 Initialize the :c:type:`v4l2_subdev` struct as 400 Initialize the :c:type:`v4l2_subdev` struct as follows:
478 401
479 .. code-block:: c 402 .. code-block:: c
480 403
481 v4l2_i2c_subdev_init(&state->sd, clien 404 v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
482 405
483 This function will fill in all the fields of : 406 This function will fill in all the fields of :c:type:`v4l2_subdev` ensure that
484 the :c:type:`v4l2_subdev` and i2c_client both 407 the :c:type:`v4l2_subdev` and i2c_client both point to one another.
485 408
486 You should also add a helper inline function t 409 You should also add a helper inline function to go from a :c:type:`v4l2_subdev`
487 pointer to a chipname_state struct: 410 pointer to a chipname_state struct:
488 411
489 .. code-block:: c 412 .. code-block:: c
490 413
491 static inline struct chipname_state *t 414 static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
492 { 415 {
493 return container_of(sd, struct 416 return container_of(sd, struct chipname_state, sd);
494 } 417 }
495 418
496 Use this to go from the :c:type:`v4l2_subdev` 419 Use this to go from the :c:type:`v4l2_subdev` struct to the ``i2c_client``
497 struct: 420 struct:
498 421
499 .. code-block:: c 422 .. code-block:: c
500 423
501 struct i2c_client *client = v4l2_get_s 424 struct i2c_client *client = v4l2_get_subdevdata(sd);
502 425
503 And this to go from an ``i2c_client`` to a :c: 426 And this to go from an ``i2c_client`` to a :c:type:`v4l2_subdev` struct:
504 427
505 .. code-block:: c 428 .. code-block:: c
506 429
507 struct v4l2_subdev *sd = i2c_get_clien 430 struct v4l2_subdev *sd = i2c_get_clientdata(client);
508 431
509 Make sure to call 432 Make sure to call
510 :c:func:`v4l2_device_unregister_subdev`\ (:c:t 433 :c:func:`v4l2_device_unregister_subdev`\ (:c:type:`sd <v4l2_subdev>`)
511 when the ``remove()`` callback is called. This 434 when the ``remove()`` callback is called. This will unregister the sub-device
512 from the bridge driver. It is safe to call thi 435 from the bridge driver. It is safe to call this even if the sub-device was
513 never registered. 436 never registered.
514 437
515 You need to do this because when the bridge dr 438 You need to do this because when the bridge driver destroys the i2c adapter
516 the ``remove()`` callbacks are called of the i 439 the ``remove()`` callbacks are called of the i2c devices on that adapter.
517 After that the corresponding v4l2_subdev struc 440 After that the corresponding v4l2_subdev structures are invalid, so they
518 have to be unregistered first. Calling 441 have to be unregistered first. Calling
519 :c:func:`v4l2_device_unregister_subdev`\ (:c:t 442 :c:func:`v4l2_device_unregister_subdev`\ (:c:type:`sd <v4l2_subdev>`)
520 from the ``remove()`` callback ensures that th 443 from the ``remove()`` callback ensures that this is always done correctly.
521 444
522 445
523 The bridge driver also has some helper functio 446 The bridge driver also has some helper functions it can use:
524 447
525 .. code-block:: c 448 .. code-block:: c
526 449
527 struct v4l2_subdev *sd = v4l2_i2c_new_ 450 struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
528 "modul 451 "module_foo", "chipid", 0x36, NULL);
529 452
530 This loads the given module (can be ``NULL`` i 453 This loads the given module (can be ``NULL`` if no module needs to be loaded)
531 and calls :c:func:`i2c_new_client_device` with 454 and calls :c:func:`i2c_new_client_device` with the given ``i2c_adapter`` and
532 chip/address arguments. If all goes well, then 455 chip/address arguments. If all goes well, then it registers the subdev with
533 the v4l2_device. 456 the v4l2_device.
534 457
535 You can also use the last argument of :c:func: 458 You can also use the last argument of :c:func:`v4l2_i2c_new_subdev` to pass
536 an array of possible I2C addresses that it sho 459 an array of possible I2C addresses that it should probe. These probe addresses
537 are only used if the previous argument is 0. A 460 are only used if the previous argument is 0. A non-zero argument means that you
538 know the exact i2c address so in that case no 461 know the exact i2c address so in that case no probing will take place.
539 462
540 Both functions return ``NULL`` if something we 463 Both functions return ``NULL`` if something went wrong.
541 464
542 Note that the chipid you pass to :c:func:`v4l2 465 Note that the chipid you pass to :c:func:`v4l2_i2c_new_subdev` is usually
543 the same as the module name. It allows you to 466 the same as the module name. It allows you to specify a chip variant, e.g.
544 "saa7114" or "saa7115". In general though the 467 "saa7114" or "saa7115". In general though the i2c driver autodetects this.
545 The use of chipid is something that needs to b 468 The use of chipid is something that needs to be looked at more closely at a
546 later date. It differs between i2c drivers and 469 later date. It differs between i2c drivers and as such can be confusing.
547 To see which chip variants are supported you c 470 To see which chip variants are supported you can look in the i2c driver code
548 for the i2c_device_id table. This lists all th 471 for the i2c_device_id table. This lists all the possibilities.
549 472
550 There are one more helper function: 473 There are one more helper function:
551 474
552 :c:func:`v4l2_i2c_new_subdev_board` uses an :c 475 :c:func:`v4l2_i2c_new_subdev_board` uses an :c:type:`i2c_board_info` struct
553 which is passed to the i2c driver and replaces 476 which is passed to the i2c driver and replaces the irq, platform_data and addr
554 arguments. 477 arguments.
555 478
556 If the subdev supports the s_config core ops, 479 If the subdev supports the s_config core ops, then that op is called with
557 the irq and platform_data arguments after the 480 the irq and platform_data arguments after the subdev was setup.
558 481
559 The :c:func:`v4l2_i2c_new_subdev` function wil 482 The :c:func:`v4l2_i2c_new_subdev` function will call
560 :c:func:`v4l2_i2c_new_subdev_board`, internall 483 :c:func:`v4l2_i2c_new_subdev_board`, internally filling a
561 :c:type:`i2c_board_info` structure using the ` 484 :c:type:`i2c_board_info` structure using the ``client_type`` and the
562 ``addr`` to fill it. 485 ``addr`` to fill it.
563 486
564 Centrally managed subdev active state <<
565 ------------------------------------- <<
566 <<
567 Traditionally V4L2 subdev drivers maintained i <<
568 device configuration. This is often implemente <<
569 v4l2_mbus_framefmt, one entry for each pad, an <<
570 rectangles. <<
571 <<
572 In addition to the active configuration, each <<
573 v4l2_subdev_state, managed by the V4L2 core, w <<
574 configuration. <<
575 <<
576 To simplify the subdev drivers the V4L2 subdev <<
577 centrally managed active configuration represe <<
578 :c:type:`v4l2_subdev_state`. One instance of s <<
579 device configuration, is stored in the sub-dev <<
580 the :c:type:`v4l2_subdev` structure, while the <<
581 each open file handle, to store the try config <<
582 handle. <<
583 <<
584 Sub-device drivers can opt-in and use state to <<
585 by initializing the subdevice state with a cal <<
586 before registering the sub-device. They must a <<
587 to release all the allocated resources before <<
588 The core automatically allocates and initializ <<
589 handle to store the try configurations and fre <<
590 handle. <<
591 <<
592 V4L2 sub-device operations that use both the : <<
593 <v4l2-subdev-format-whence>` receive the corre <<
594 the 'state' parameter. The state must be locke <<
595 caller by calling :c:func:`v4l2_subdev_lock_st <<
596 :c:func:`v4l2_subdev_unlock_state()`. The call <<
597 operation through the :c:func:`v4l2_subdev_cal <<
598 <<
599 Operations that do not receive a state paramet <<
600 subdevice active state, which drivers can excl <<
601 calling :c:func:`v4l2_subdev_lock_and_get_acti <<
602 state must equally be released by calling :c:f <<
603 <<
604 Drivers must never manually access the state s <<
605 or in the file handle without going through th <<
606 <<
607 While the V4L2 core passes the correct try or <<
608 operations, many existing device drivers pass <<
609 operations with :c:func:`v4l2_subdev_call()`. <<
610 issues with subdevice drivers that let the V4L <<
611 as they expect to receive the appropriate stat <<
612 conversion of subdevice drivers to a managed a <<
613 convert all callers at the same time, an addit <<
614 added to v4l2_subdev_call(), which handles the <<
615 the callee's active state with :c:func:`v4l2_s <<
616 and unlocking the state after the call. <<
617 <<
618 The whole subdev state is in reality split int <<
619 v4l2_subdev_state, subdev controls and subdev <<
620 future these parts should be combined into a s <<
621 we need a way to handle the locking for these <<
622 by sharing a lock. The v4l2_ctrl_handler alrea <<
623 pointer and the same model is used with states <<
624 before calling v4l2_subdev_init_finalize(): <<
625 <<
626 .. code-block:: c <<
627 <<
628 sd->ctrl_handler->lock = &priv->mutex; <<
629 sd->state_lock = &priv->mutex; <<
630 <<
631 This shares the driver's private mutex between <<
632 <<
633 Streams, multiplexed media pads and internal r <<
634 ---------------------------------------------- <<
635 <<
636 A subdevice driver can implement support for m <<
637 the V4L2_SUBDEV_FL_STREAMS subdev flag and imp <<
638 centrally managed subdev active state, routing <<
639 configuration. <<
640 <<
641 V4L2 sub-device functions and data structures 487 V4L2 sub-device functions and data structures
642 --------------------------------------------- 488 ---------------------------------------------
643 489
644 .. kernel-doc:: include/media/v4l2-subdev.h 490 .. kernel-doc:: include/media/v4l2-subdev.h
>> 491
>> 492 .. kernel-doc:: include/media/v4l2-async.h
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