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 exist 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 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 a sub-device driver implements sink pads, the subdev driver may set the
126 link_validate field in :c:type:`v4l2_subdev_pa 126 link_validate field in :c:type:`v4l2_subdev_pad_ops` to provide its own link
127 validation function. For every link in the pip 127 validation function. For every link in the pipeline, the link_validate pad
128 operation of the sink end of the link is calle 128 operation of the sink end of the link is called. In both cases the driver is
129 still responsible for validating the correctne 129 still responsible for validating the correctness of the format configuration
130 between sub-devices and video nodes. 130 between sub-devices and video nodes.
131 131
132 If link_validate op is not set, the default fu 132 If link_validate op is not set, the default function
133 :c:func:`v4l2_subdev_link_validate_default` is 133 :c:func:`v4l2_subdev_link_validate_default` is used instead. This function
134 ensures that width, height and the media bus p 134 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 135 and sink of the link. Subdev drivers are also free to use this function to
136 perform the checks mentioned above in addition 136 perform the checks mentioned above in addition to their own checks.
137 137
138 Subdev registration 138 Subdev registration
139 ~~~~~~~~~~~~~~~~~~~ 139 ~~~~~~~~~~~~~~~~~~~
140 140
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 <<
161 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
162 <<
163 In the **synchronous** case a device (bridge) 160 In the **synchronous** case a device (bridge) driver needs to register the
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: <<
185 <<
186 Registering asynchronous sub-devices <<
187 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
188 <<
189 In the **asynchronous** case subdevice probing 182 In the **asynchronous** case subdevice probing can be invoked independently of
190 the bridge driver availability. The subdevice 183 the bridge driver availability. The subdevice driver then has to verify whether
191 all the requirements for a successful probing 184 all the requirements for a successful probing are satisfied. This can include a
192 check for a master clock availability. If any 185 check for a master clock availability. If any of the conditions aren't satisfied
193 the driver might decide to return ``-EPROBE_DE 186 the driver might decide to return ``-EPROBE_DEFER`` to request further reprobing
194 attempts. Once all conditions are met the subd 187 attempts. Once all conditions are met the subdevice shall be registered using
195 the :c:func:`v4l2_async_register_subdev` funct 188 the :c:func:`v4l2_async_register_subdev` function. Unregistration is
196 performed using the :c:func:`v4l2_async_unregi 189 performed using the :c:func:`v4l2_async_unregister_subdev` call. Subdevices
197 registered this way are stored in a global lis 190 registered this way are stored in a global list of subdevices, ready to be
198 picked up by bridge drivers. 191 picked up by bridge drivers.
199 192
200 Drivers must complete all initialization of th !! 193 Bridge drivers in turn have to register a notifier object. This is
201 registering it using :c:func:`v4l2_async_regis !! 194 performed using the :c:func:`v4l2_async_nf_register` call. To
202 enabling runtime PM. This is because the sub-d !! 195 unregister the notifier the driver has to call
203 as soon as it gets registered. !! 196 :c:func:`v4l2_async_nf_unregister`. The former of the two functions
204 !! 197 takes two arguments: a pointer to struct :c:type:`v4l2_device` and a
205 Asynchronous sub-device notifiers !! 198 pointer to struct :c:type:`v4l2_async_notifier`.
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`. <<
213 199
214 Before registering the notifier, bridge driver 200 Before registering the notifier, bridge drivers must do two things: first, the
215 notifier must be initialized using the :c:func !! 201 notifier must be initialized using the :c:func:`v4l2_async_nf_init`.
216 bridge drivers can then begin to form a list o !! 202 Second, bridge drivers can then begin to form a list of subdevice descriptors
217 that the bridge device needs for its !! 203 that the bridge device needs for its operation. Several functions are available
218 operation. :c:func:`v4l2_async_nf_add_fwnode`, !! 204 to add subdevice descriptors to a notifier, depending on the type of device and
219 :c:func:`v4l2_async_nf_add_fwnode_remote` and !! 205 the needs of the driver.
220 !! 206
221 Async connection descriptors describe connecti !! 207 :c:func:`v4l2_async_nf_add_fwnode_remote` and
222 drivers for which are not yet probed. Based on !! 208 :c:func:`v4l2_async_nf_add_i2c` are for bridge and ISP drivers for
223 or ancillary link may be created when the rela !! 209 registering their async sub-devices with the notifier.
224 available. There may be one or more async conn !! 210
225 this is not known at the time of adding the co !! 211 :c:func:`v4l2_async_register_subdev_sensor` is a helper function for
226 connections are bound as matching async sub-de !! 212 sensor drivers registering their own async sub-device, but it also registers a
227 !! 213 notifier and further registers async sub-devices for lens and flash devices
228 Asynchronous sub-device notifier for sub-devic !! 214 found in firmware. The notifier for the sub-device is unregistered with the
229 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ !! 215 async sub-device.
230 !! 216
231 A driver that registers an asynchronous sub-de !! 217 These functions allocate an async sub-device descriptor which is of type struct
232 asynchronous notifier. This is called an async !! 218 :c:type:`v4l2_async_subdev` embedded in a driver-specific struct. The &struct
233 process is similar to that of a bridge driver !! 219 :c:type:`v4l2_async_subdev` shall be the first member of this struct:
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 <<
254 220
255 .. code-block:: c 221 .. code-block:: c
256 222
257 struct my_async_connection { !! 223 struct my_async_subdev {
258 struct v4l2_async_connection a !! 224 struct v4l2_async_subdev asd;
259 ... 225 ...
260 }; 226 };
261 227
262 struct my_async_connection *my_asc; !! 228 struct my_async_subdev *my_asd;
263 struct fwnode_handle *ep; 229 struct fwnode_handle *ep;
264 230
265 ... 231 ...
266 232
267 my_asc = v4l2_async_nf_add_fwnode_remo !! 233 my_asd = v4l2_async_nf_add_fwnode_remote(¬ifier, ep,
268 !! 234 struct my_async_subdev);
269 fwnode_handle_put(ep); 235 fwnode_handle_put(ep);
270 236
271 if (IS_ERR(my_asc)) !! 237 if (IS_ERR(asd))
272 return PTR_ERR(my_asc); !! 238 return PTR_ERR(asd);
273 <<
274 Asynchronous sub-device notifier callbacks <<
275 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ <<
276 239
277 The V4L2 core will then use these connection d !! 240 The V4L2 core will then use these descriptors to match asynchronously
278 registered subdevices to them. If a match is d !! 241 registered subdevices to them. If a match is detected the ``.bound()``
279 callback is called. After all connections have !! 242 notifier callback is called. After all subdevices have been located the
280 callback is called. When a connection is remov !! 243 .complete() callback is called. When a subdevice is removed from the
281 ``.unbind()`` method is called. All three call !! 244 system the .unbind() method is called. All three callbacks are optional.
282 245
283 Drivers can store any type of custom data in t 246 Drivers can store any type of custom data in their driver-specific
284 :c:type:`v4l2_async_connection` wrapper. If an !! 247 :c:type:`v4l2_async_subdev` wrapper. If any of that data requires special
285 handling when the structure is freed, drivers 248 handling when the structure is freed, drivers must implement the ``.destroy()``
286 notifier callback. The framework will call it 249 notifier callback. The framework will call it right before freeing the
287 :c:type:`v4l2_async_connection`. !! 250 :c:type:`v4l2_async_subdev`.
288 251
289 Calling subdev operations 252 Calling subdev operations
290 ~~~~~~~~~~~~~~~~~~~~~~~~~ 253 ~~~~~~~~~~~~~~~~~~~~~~~~~
291 254
292 The advantage of using :c:type:`v4l2_subdev` i 255 The advantage of using :c:type:`v4l2_subdev` is that it is a generic struct and
293 does not contain any knowledge about the under 256 does not contain any knowledge about the underlying hardware. So a driver might
294 contain several subdevs that use an I2C bus, b 257 contain several subdevs that use an I2C bus, but also a subdev that is
295 controlled through GPIO pins. This distinction 258 controlled through GPIO pins. This distinction is only relevant when setting
296 up the device, but once the subdev is register 259 up the device, but once the subdev is registered it is completely transparent.
297 260
298 Once the subdev has been registered you can ca 261 Once the subdev has been registered you can call an ops function either
299 directly: 262 directly:
300 263
301 .. code-block:: c 264 .. code-block:: c
302 265
303 err = sd->ops->core->g_std(sd, &norm); 266 err = sd->ops->core->g_std(sd, &norm);
304 267
305 but it is better and easier to use this macro: 268 but it is better and easier to use this macro:
306 269
307 .. code-block:: c 270 .. code-block:: c
308 271
309 err = v4l2_subdev_call(sd, core, g_std 272 err = v4l2_subdev_call(sd, core, g_std, &norm);
310 273
311 The macro will do the right ``NULL`` pointer c 274 The macro will do the right ``NULL`` pointer checks and returns ``-ENODEV``
312 if :c:type:`sd <v4l2_subdev>` is ``NULL``, ``- 275 if :c:type:`sd <v4l2_subdev>` is ``NULL``, ``-ENOIOCTLCMD`` if either
313 :c:type:`sd <v4l2_subdev>`->core or :c:type:`s 276 :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 277 :c:type:`sd <v4l2_subdev>`->ops->core->g_std ops.
315 278
316 It is also possible to call all or a subset of 279 It is also possible to call all or a subset of the sub-devices:
317 280
318 .. code-block:: c 281 .. code-block:: c
319 282
320 v4l2_device_call_all(v4l2_dev, 0, core 283 v4l2_device_call_all(v4l2_dev, 0, core, g_std, &norm);
321 284
322 Any subdev that does not support this ops is s 285 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 286 ignored. If you want to check for errors use this:
324 287
325 .. code-block:: c 288 .. code-block:: c
326 289
327 err = v4l2_device_call_until_err(v4l2_ 290 err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_std, &norm);
328 291
329 Any error except ``-ENOIOCTLCMD`` will exit th 292 Any error except ``-ENOIOCTLCMD`` will exit the loop with that error. If no
330 errors (except ``-ENOIOCTLCMD``) occurred, the 293 errors (except ``-ENOIOCTLCMD``) occurred, then 0 is returned.
331 294
332 The second argument to both calls is a group I 295 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 296 called. If non-zero, then only those whose group ID match that value will
334 be called. Before a bridge driver registers a 297 be called. Before a bridge driver registers a subdev it can set
335 :c:type:`sd <v4l2_subdev>`->grp_id to whatever 298 :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 299 default). This value is owned by the bridge driver and the sub-device driver
337 will never modify or use it. 300 will never modify or use it.
338 301
339 The group ID gives the bridge driver more cont 302 The group ID gives the bridge driver more control how callbacks are called.
340 For example, there may be multiple audio chips 303 For example, there may be multiple audio chips on a board, each capable of
341 changing the volume. But usually only one will 304 changing the volume. But usually only one will actually be used when the
342 user want to change the volume. You can set th 305 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 306 e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling
344 ``v4l2_device_call_all()``. That ensures that 307 ``v4l2_device_call_all()``. That ensures that it will only go to the subdev
345 that needs it. 308 that needs it.
346 309
347 If the sub-device needs to notify its v4l2_dev 310 If the sub-device needs to notify its v4l2_device parent of an event, then
348 it can call ``v4l2_subdev_notify(sd, notificat 311 it can call ``v4l2_subdev_notify(sd, notification, arg)``. This macro checks
349 whether there is a ``notify()`` callback defin 312 whether there is a ``notify()`` callback defined and returns ``-ENODEV`` if not.
350 Otherwise the result of the ``notify()`` call 313 Otherwise the result of the ``notify()`` call is returned.
351 314
352 V4L2 sub-device userspace API 315 V4L2 sub-device userspace API
353 ----------------------------- 316 -----------------------------
354 317
355 Bridge drivers traditionally expose one or mul 318 Bridge drivers traditionally expose one or multiple video nodes to userspace,
356 and control subdevices through the :c:type:`v4 319 and control subdevices through the :c:type:`v4l2_subdev_ops` operations in
357 response to video node operations. This hides 320 response to video node operations. This hides the complexity of the underlying
358 hardware from applications. For complex device 321 hardware from applications. For complex devices, finer-grained control of the
359 device than what the video nodes offer may be 322 device than what the video nodes offer may be required. In those cases, bridge
360 drivers that implement :ref:`the media control 323 drivers that implement :ref:`the media controller API <media_controller>` may
361 opt for making the subdevice operations direct 324 opt for making the subdevice operations directly accessible from userspace.
362 325
363 Device nodes named ``v4l-subdev``\ *X* can be 326 Device nodes named ``v4l-subdev``\ *X* can be created in ``/dev`` to access
364 sub-devices directly. If a sub-device supports 327 sub-devices directly. If a sub-device supports direct userspace configuration
365 it must set the ``V4L2_SUBDEV_FL_HAS_DEVNODE`` 328 it must set the ``V4L2_SUBDEV_FL_HAS_DEVNODE`` flag before being registered.
366 329
367 After registering sub-devices, the :c:type:`v4 330 After registering sub-devices, the :c:type:`v4l2_device` driver can create
368 device nodes for all registered sub-devices ma 331 device nodes for all registered sub-devices marked with
369 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` by calling 332 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` by calling
370 :c:func:`v4l2_device_register_subdev_nodes`. T 333 :c:func:`v4l2_device_register_subdev_nodes`. Those device nodes will be
371 automatically removed when sub-devices are unr 334 automatically removed when sub-devices are unregistered.
372 335
373 The device node handles a subset of the V4L2 A 336 The device node handles a subset of the V4L2 API.
374 337
375 ``VIDIOC_QUERYCTRL``, 338 ``VIDIOC_QUERYCTRL``,
376 ``VIDIOC_QUERYMENU``, 339 ``VIDIOC_QUERYMENU``,
377 ``VIDIOC_G_CTRL``, 340 ``VIDIOC_G_CTRL``,
378 ``VIDIOC_S_CTRL``, 341 ``VIDIOC_S_CTRL``,
379 ``VIDIOC_G_EXT_CTRLS``, 342 ``VIDIOC_G_EXT_CTRLS``,
380 ``VIDIOC_S_EXT_CTRLS`` and 343 ``VIDIOC_S_EXT_CTRLS`` and
381 ``VIDIOC_TRY_EXT_CTRLS``: 344 ``VIDIOC_TRY_EXT_CTRLS``:
382 345
383 The controls ioctls are identical to t 346 The controls ioctls are identical to the ones defined in V4L2. They
384 behave identically, with the only exce 347 behave identically, with the only exception that they deal only with
385 controls implemented in the sub-device 348 controls implemented in the sub-device. Depending on the driver, those
386 controls can be also be accessed throu 349 controls can be also be accessed through one (or several) V4L2 device
387 nodes. 350 nodes.
388 351
389 ``VIDIOC_DQEVENT``, 352 ``VIDIOC_DQEVENT``,
390 ``VIDIOC_SUBSCRIBE_EVENT`` and 353 ``VIDIOC_SUBSCRIBE_EVENT`` and
391 ``VIDIOC_UNSUBSCRIBE_EVENT`` 354 ``VIDIOC_UNSUBSCRIBE_EVENT``
392 355
393 The events ioctls are identical to the 356 The events ioctls are identical to the ones defined in V4L2. They
394 behave identically, with the only exce 357 behave identically, with the only exception that they deal only with
395 events generated by the sub-device. De 358 events generated by the sub-device. Depending on the driver, those
396 events can also be reported by one (or 359 events can also be reported by one (or several) V4L2 device nodes.
397 360
398 Sub-device drivers that want to use ev 361 Sub-device drivers that want to use events need to set the
399 ``V4L2_SUBDEV_FL_HAS_EVENTS`` :c:type: 362 ``V4L2_SUBDEV_FL_HAS_EVENTS`` :c:type:`v4l2_subdev`.flags before registering
400 the sub-device. After registration eve 363 the sub-device. After registration events can be queued as usual on the
401 :c:type:`v4l2_subdev`.devnode device n 364 :c:type:`v4l2_subdev`.devnode device node.
402 365
403 To properly support events, the ``poll 366 To properly support events, the ``poll()`` file operation is also
404 implemented. 367 implemented.
405 368
406 Private ioctls 369 Private ioctls
407 370
408 All ioctls not in the above list are p 371 All ioctls not in the above list are passed directly to the sub-device
409 driver through the core::ioctl operati 372 driver through the core::ioctl operation.
410 373
411 Read-only sub-device userspace API 374 Read-only sub-device userspace API
412 ---------------------------------- 375 ----------------------------------
413 376
414 Bridge drivers that control their connected su 377 Bridge drivers that control their connected subdevices through direct calls to
415 the kernel API realized by :c:type:`v4l2_subde 378 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 379 want userspace to be able to change the same parameters through the subdevice
417 device node and thus do not usually register a 380 device node and thus do not usually register any.
418 381
419 It is sometimes useful to report to userspace 382 It is sometimes useful to report to userspace the current subdevice
420 configuration through a read-only API, that do 383 configuration through a read-only API, that does not permit applications to
421 change to the device parameters but allows int 384 change to the device parameters but allows interfacing to the subdevice device
422 node to inspect them. 385 node to inspect them.
423 386
424 For instance, to implement cameras based on co 387 For instance, to implement cameras based on computational photography, userspace
425 needs to know the detailed camera sensor confi 388 needs to know the detailed camera sensor configuration (in terms of skipping,
426 binning, cropping and scaling) for each suppor 389 binning, cropping and scaling) for each supported output resolution. To support
427 such use cases, bridge drivers may expose the 390 such use cases, bridge drivers may expose the subdevice operations to userspace
428 through a read-only API. 391 through a read-only API.
429 392
430 To create a read-only device node for all the 393 To create a read-only device node for all the subdevices registered with the
431 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` set, the :c:typ 394 ``V4L2_SUBDEV_FL_HAS_DEVNODE`` set, the :c:type:`v4l2_device` driver should call
432 :c:func:`v4l2_device_register_ro_subdev_nodes` 395 :c:func:`v4l2_device_register_ro_subdev_nodes`.
433 396
434 Access to the following ioctls for userspace a 397 Access to the following ioctls for userspace applications is restricted on
435 sub-device device nodes registered with 398 sub-device device nodes registered with
436 :c:func:`v4l2_device_register_ro_subdev_nodes` 399 :c:func:`v4l2_device_register_ro_subdev_nodes`.
437 400
438 ``VIDIOC_SUBDEV_S_FMT``, 401 ``VIDIOC_SUBDEV_S_FMT``,
439 ``VIDIOC_SUBDEV_S_CROP``, 402 ``VIDIOC_SUBDEV_S_CROP``,
440 ``VIDIOC_SUBDEV_S_SELECTION``: 403 ``VIDIOC_SUBDEV_S_SELECTION``:
441 404
442 These ioctls are only allowed on a rea 405 These ioctls are only allowed on a read-only subdevice device node
443 for the :ref:`V4L2_SUBDEV_FORMAT_TRY < 406 for the :ref:`V4L2_SUBDEV_FORMAT_TRY <v4l2-subdev-format-whence>`
444 formats and selection rectangles. 407 formats and selection rectangles.
445 408
446 ``VIDIOC_SUBDEV_S_FRAME_INTERVAL``, 409 ``VIDIOC_SUBDEV_S_FRAME_INTERVAL``,
447 ``VIDIOC_SUBDEV_S_DV_TIMINGS``, 410 ``VIDIOC_SUBDEV_S_DV_TIMINGS``,
448 ``VIDIOC_SUBDEV_S_STD``: 411 ``VIDIOC_SUBDEV_S_STD``:
449 412
450 These ioctls are not allowed on a read 413 These ioctls are not allowed on a read-only subdevice node.
451 414
452 In case the ioctl is not allowed, or the forma 415 In case the ioctl is not allowed, or the format to modify is set to
453 ``V4L2_SUBDEV_FORMAT_ACTIVE``, the core return 416 ``V4L2_SUBDEV_FORMAT_ACTIVE``, the core returns a negative error code and
454 the errno variable is set to ``-EPERM``. 417 the errno variable is set to ``-EPERM``.
455 418
456 I2C sub-device drivers 419 I2C sub-device drivers
457 ---------------------- 420 ----------------------
458 421
459 Since these drivers are so common, special hel 422 Since these drivers are so common, special helper functions are available to
460 ease the use of these drivers (``v4l2-common.h 423 ease the use of these drivers (``v4l2-common.h``).
461 424
462 The recommended method of adding :c:type:`v4l2 425 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 426 is to embed the :c:type:`v4l2_subdev` struct into the state struct that is
464 created for each I2C device instance. Very sim 427 created for each I2C device instance. Very simple devices have no state
465 struct and in that case you can just create a 428 struct and in that case you can just create a :c:type:`v4l2_subdev` directly.
466 429
467 A typical state struct would look like this (w 430 A typical state struct would look like this (where 'chipname' is replaced by
468 the name of the chip): 431 the name of the chip):
469 432
470 .. code-block:: c 433 .. code-block:: c
471 434
472 struct chipname_state { 435 struct chipname_state {
473 struct v4l2_subdev sd; 436 struct v4l2_subdev sd;
474 ... /* additional state field 437 ... /* additional state fields */
475 }; 438 };
476 439
477 Initialize the :c:type:`v4l2_subdev` struct as 440 Initialize the :c:type:`v4l2_subdev` struct as follows:
478 441
479 .. code-block:: c 442 .. code-block:: c
480 443
481 v4l2_i2c_subdev_init(&state->sd, clien 444 v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
482 445
483 This function will fill in all the fields of : 446 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 447 the :c:type:`v4l2_subdev` and i2c_client both point to one another.
485 448
486 You should also add a helper inline function t 449 You should also add a helper inline function to go from a :c:type:`v4l2_subdev`
487 pointer to a chipname_state struct: 450 pointer to a chipname_state struct:
488 451
489 .. code-block:: c 452 .. code-block:: c
490 453
491 static inline struct chipname_state *t 454 static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
492 { 455 {
493 return container_of(sd, struct 456 return container_of(sd, struct chipname_state, sd);
494 } 457 }
495 458
496 Use this to go from the :c:type:`v4l2_subdev` 459 Use this to go from the :c:type:`v4l2_subdev` struct to the ``i2c_client``
497 struct: 460 struct:
498 461
499 .. code-block:: c 462 .. code-block:: c
500 463
501 struct i2c_client *client = v4l2_get_s 464 struct i2c_client *client = v4l2_get_subdevdata(sd);
502 465
503 And this to go from an ``i2c_client`` to a :c: 466 And this to go from an ``i2c_client`` to a :c:type:`v4l2_subdev` struct:
504 467
505 .. code-block:: c 468 .. code-block:: c
506 469
507 struct v4l2_subdev *sd = i2c_get_clien 470 struct v4l2_subdev *sd = i2c_get_clientdata(client);
508 471
509 Make sure to call 472 Make sure to call
510 :c:func:`v4l2_device_unregister_subdev`\ (:c:t 473 :c:func:`v4l2_device_unregister_subdev`\ (:c:type:`sd <v4l2_subdev>`)
511 when the ``remove()`` callback is called. This 474 when the ``remove()`` callback is called. This will unregister the sub-device
512 from the bridge driver. It is safe to call thi 475 from the bridge driver. It is safe to call this even if the sub-device was
513 never registered. 476 never registered.
514 477
515 You need to do this because when the bridge dr 478 You need to do this because when the bridge driver destroys the i2c adapter
516 the ``remove()`` callbacks are called of the i 479 the ``remove()`` callbacks are called of the i2c devices on that adapter.
517 After that the corresponding v4l2_subdev struc 480 After that the corresponding v4l2_subdev structures are invalid, so they
518 have to be unregistered first. Calling 481 have to be unregistered first. Calling
519 :c:func:`v4l2_device_unregister_subdev`\ (:c:t 482 :c:func:`v4l2_device_unregister_subdev`\ (:c:type:`sd <v4l2_subdev>`)
520 from the ``remove()`` callback ensures that th 483 from the ``remove()`` callback ensures that this is always done correctly.
521 484
522 485
523 The bridge driver also has some helper functio 486 The bridge driver also has some helper functions it can use:
524 487
525 .. code-block:: c 488 .. code-block:: c
526 489
527 struct v4l2_subdev *sd = v4l2_i2c_new_ 490 struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
528 "modul 491 "module_foo", "chipid", 0x36, NULL);
529 492
530 This loads the given module (can be ``NULL`` i 493 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 494 and calls :c:func:`i2c_new_client_device` with the given ``i2c_adapter`` and
532 chip/address arguments. If all goes well, then 495 chip/address arguments. If all goes well, then it registers the subdev with
533 the v4l2_device. 496 the v4l2_device.
534 497
535 You can also use the last argument of :c:func: 498 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 499 an array of possible I2C addresses that it should probe. These probe addresses
537 are only used if the previous argument is 0. A 500 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 501 know the exact i2c address so in that case no probing will take place.
539 502
540 Both functions return ``NULL`` if something we 503 Both functions return ``NULL`` if something went wrong.
541 504
542 Note that the chipid you pass to :c:func:`v4l2 505 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 506 the same as the module name. It allows you to specify a chip variant, e.g.
544 "saa7114" or "saa7115". In general though the 507 "saa7114" or "saa7115". In general though the i2c driver autodetects this.
545 The use of chipid is something that needs to b 508 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 509 later date. It differs between i2c drivers and as such can be confusing.
547 To see which chip variants are supported you c 510 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 511 for the i2c_device_id table. This lists all the possibilities.
549 512
550 There are one more helper function: 513 There are one more helper function:
551 514
552 :c:func:`v4l2_i2c_new_subdev_board` uses an :c 515 :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 516 which is passed to the i2c driver and replaces the irq, platform_data and addr
554 arguments. 517 arguments.
555 518
556 If the subdev supports the s_config core ops, 519 If the subdev supports the s_config core ops, then that op is called with
557 the irq and platform_data arguments after the 520 the irq and platform_data arguments after the subdev was setup.
558 521
559 The :c:func:`v4l2_i2c_new_subdev` function wil 522 The :c:func:`v4l2_i2c_new_subdev` function will call
560 :c:func:`v4l2_i2c_new_subdev_board`, internall 523 :c:func:`v4l2_i2c_new_subdev_board`, internally filling a
561 :c:type:`i2c_board_info` structure using the ` 524 :c:type:`i2c_board_info` structure using the ``client_type`` and the
562 ``addr`` to fill it. 525 ``addr`` to fill it.
563 526
564 Centrally managed subdev active state 527 Centrally managed subdev active state
565 ------------------------------------- 528 -------------------------------------
566 529
567 Traditionally V4L2 subdev drivers maintained i 530 Traditionally V4L2 subdev drivers maintained internal state for the active
568 device configuration. This is often implemente 531 device configuration. This is often implemented as e.g. an array of struct
569 v4l2_mbus_framefmt, one entry for each pad, an 532 v4l2_mbus_framefmt, one entry for each pad, and similarly for crop and compose
570 rectangles. 533 rectangles.
571 534
572 In addition to the active configuration, each !! 535 In addition to the active configuration, each subdev file handle has an array of
573 v4l2_subdev_state, managed by the V4L2 core, w !! 536 struct v4l2_subdev_pad_config, managed by the V4L2 core, which contains the try
574 configuration. 537 configuration.
575 538
576 To simplify the subdev drivers the V4L2 subdev 539 To simplify the subdev drivers the V4L2 subdev API now optionally supports a
577 centrally managed active configuration represe 540 centrally managed active configuration represented by
578 :c:type:`v4l2_subdev_state`. One instance of s 541 :c:type:`v4l2_subdev_state`. One instance of state, which contains the active
579 device configuration, is stored in the sub-dev 542 device configuration, is stored in the sub-device itself as part of
580 the :c:type:`v4l2_subdev` structure, while the 543 the :c:type:`v4l2_subdev` structure, while the core associates a try state to
581 each open file handle, to store the try config 544 each open file handle, to store the try configuration related to that file
582 handle. 545 handle.
583 546
584 Sub-device drivers can opt-in and use state to 547 Sub-device drivers can opt-in and use state to manage their active configuration
585 by initializing the subdevice state with a cal 548 by initializing the subdevice state with a call to v4l2_subdev_init_finalize()
586 before registering the sub-device. They must a 549 before registering the sub-device. They must also call v4l2_subdev_cleanup()
587 to release all the allocated resources before 550 to release all the allocated resources before unregistering the sub-device.
588 The core automatically allocates and initializ 551 The core automatically allocates and initializes a state for each open file
589 handle to store the try configurations and fre 552 handle to store the try configurations and frees it when closing the file
590 handle. 553 handle.
591 554
592 V4L2 sub-device operations that use both the : 555 V4L2 sub-device operations that use both the :ref:`ACTIVE and TRY formats
593 <v4l2-subdev-format-whence>` receive the corre 556 <v4l2-subdev-format-whence>` receive the correct state to operate on through
594 the 'state' parameter. The state must be locke 557 the 'state' parameter. The state must be locked and unlocked by the
595 caller by calling :c:func:`v4l2_subdev_lock_st 558 caller by calling :c:func:`v4l2_subdev_lock_state()` and
596 :c:func:`v4l2_subdev_unlock_state()`. The call 559 :c:func:`v4l2_subdev_unlock_state()`. The caller can do so by calling the subdev
597 operation through the :c:func:`v4l2_subdev_cal 560 operation through the :c:func:`v4l2_subdev_call_state_active()` macro.
598 561
599 Operations that do not receive a state paramet 562 Operations that do not receive a state parameter implicitly operate on the
600 subdevice active state, which drivers can excl 563 subdevice active state, which drivers can exclusively access by
601 calling :c:func:`v4l2_subdev_lock_and_get_acti 564 calling :c:func:`v4l2_subdev_lock_and_get_active_state()`. The sub-device active
602 state must equally be released by calling :c:f 565 state must equally be released by calling :c:func:`v4l2_subdev_unlock_state()`.
603 566
604 Drivers must never manually access the state s 567 Drivers must never manually access the state stored in the :c:type:`v4l2_subdev`
605 or in the file handle without going through th 568 or in the file handle without going through the designated helpers.
606 569
607 While the V4L2 core passes the correct try or 570 While the V4L2 core passes the correct try or active state to the subdevice
608 operations, many existing device drivers pass 571 operations, many existing device drivers pass a NULL state when calling
609 operations with :c:func:`v4l2_subdev_call()`. 572 operations with :c:func:`v4l2_subdev_call()`. This legacy construct causes
610 issues with subdevice drivers that let the V4L 573 issues with subdevice drivers that let the V4L2 core manage the active state,
611 as they expect to receive the appropriate stat 574 as they expect to receive the appropriate state as a parameter. To help the
612 conversion of subdevice drivers to a managed a 575 conversion of subdevice drivers to a managed active state without having to
613 convert all callers at the same time, an addit 576 convert all callers at the same time, an additional wrapper layer has been
614 added to v4l2_subdev_call(), which handles the 577 added to v4l2_subdev_call(), which handles the NULL case by getting and locking
615 the callee's active state with :c:func:`v4l2_s 578 the callee's active state with :c:func:`v4l2_subdev_lock_and_get_active_state()`,
616 and unlocking the state after the call. 579 and unlocking the state after the call.
617 580
618 The whole subdev state is in reality split int 581 The whole subdev state is in reality split into three parts: the
619 v4l2_subdev_state, subdev controls and subdev 582 v4l2_subdev_state, subdev controls and subdev driver's internal state. In the
620 future these parts should be combined into a s 583 future these parts should be combined into a single state. For the time being
621 we need a way to handle the locking for these 584 we need a way to handle the locking for these parts. This can be accomplished
622 by sharing a lock. The v4l2_ctrl_handler alrea 585 by sharing a lock. The v4l2_ctrl_handler already supports this via its 'lock'
623 pointer and the same model is used with states 586 pointer and the same model is used with states. The driver can do the following
624 before calling v4l2_subdev_init_finalize(): 587 before calling v4l2_subdev_init_finalize():
625 588
626 .. code-block:: c 589 .. code-block:: c
627 590
628 sd->ctrl_handler->lock = &priv->mutex; 591 sd->ctrl_handler->lock = &priv->mutex;
629 sd->state_lock = &priv->mutex; 592 sd->state_lock = &priv->mutex;
630 593
631 This shares the driver's private mutex between 594 This shares the driver's private mutex between the controls and the states.
632 595
633 Streams, multiplexed media pads and internal r 596 Streams, multiplexed media pads and internal routing
634 ---------------------------------------------- 597 ----------------------------------------------------
635 598
636 A subdevice driver can implement support for m 599 A subdevice driver can implement support for multiplexed streams by setting
637 the V4L2_SUBDEV_FL_STREAMS subdev flag and imp 600 the V4L2_SUBDEV_FL_STREAMS subdev flag and implementing support for
638 centrally managed subdev active state, routing 601 centrally managed subdev active state, routing and stream based
639 configuration. 602 configuration.
640 603
641 V4L2 sub-device functions and data structures 604 V4L2 sub-device functions and data structures
642 --------------------------------------------- 605 ---------------------------------------------
643 606
644 .. kernel-doc:: include/media/v4l2-subdev.h 607 .. kernel-doc:: include/media/v4l2-subdev.h
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