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2a1fcdf0 HV |
1 | Overview of the V4L2 driver framework |
2 | ===================================== | |
3 | ||
4 | This text documents the various structures provided by the V4L2 framework and | |
5 | their relationships. | |
6 | ||
7 | ||
8 | Introduction | |
9 | ------------ | |
10 | ||
11 | The V4L2 drivers tend to be very complex due to the complexity of the | |
12 | hardware: most devices have multiple ICs, export multiple device nodes in | |
13 | /dev, and create also non-V4L2 devices such as DVB, ALSA, FB, I2C and input | |
14 | (IR) devices. | |
15 | ||
16 | Especially the fact that V4L2 drivers have to setup supporting ICs to | |
17 | do audio/video muxing/encoding/decoding makes it more complex than most. | |
18 | Usually these ICs are connected to the main bridge driver through one or | |
19 | more I2C busses, but other busses can also be used. Such devices are | |
20 | called 'sub-devices'. | |
21 | ||
22 | For a long time the framework was limited to the video_device struct for | |
23 | creating V4L device nodes and video_buf for handling the video buffers | |
24 | (note that this document does not discuss the video_buf framework). | |
25 | ||
26 | This meant that all drivers had to do the setup of device instances and | |
27 | connecting to sub-devices themselves. Some of this is quite complicated | |
28 | to do right and many drivers never did do it correctly. | |
29 | ||
30 | There is also a lot of common code that could never be refactored due to | |
31 | the lack of a framework. | |
32 | ||
33 | So this framework sets up the basic building blocks that all drivers | |
34 | need and this same framework should make it much easier to refactor | |
35 | common code into utility functions shared by all drivers. | |
36 | ||
37 | ||
38 | Structure of a driver | |
39 | --------------------- | |
40 | ||
41 | All drivers have the following structure: | |
42 | ||
43 | 1) A struct for each device instance containing the device state. | |
44 | ||
45 | 2) A way of initializing and commanding sub-devices (if any). | |
46 | ||
f44026db HV |
47 | 3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX and /dev/radioX) |
48 | and keeping track of device-node specific data. | |
2a1fcdf0 | 49 | |
44061c05 MCC |
50 | 4) Filehandle-specific structs containing per-filehandle data; |
51 | ||
52 | 5) video buffer handling. | |
2a1fcdf0 HV |
53 | |
54 | This is a rough schematic of how it all relates: | |
55 | ||
56 | device instances | |
57 | | | |
58 | +-sub-device instances | |
59 | | | |
60 | \-V4L2 device nodes | |
61 | | | |
62 | \-filehandle instances | |
63 | ||
64 | ||
65 | Structure of the framework | |
66 | -------------------------- | |
67 | ||
68 | The framework closely resembles the driver structure: it has a v4l2_device | |
69 | struct for the device instance data, a v4l2_subdev struct to refer to | |
70 | sub-device instances, the video_device struct stores V4L2 device node data | |
f818b358 | 71 | and the v4l2_fh struct keeps track of filehandle instances. |
2a1fcdf0 | 72 | |
2c0ab67b LP |
73 | The V4L2 framework also optionally integrates with the media framework. If a |
74 | driver sets the struct v4l2_device mdev field, sub-devices and video nodes | |
75 | will automatically appear in the media framework as entities. | |
76 | ||
2a1fcdf0 HV |
77 | |
78 | struct v4l2_device | |
79 | ------------------ | |
80 | ||
81 | Each device instance is represented by a struct v4l2_device (v4l2-device.h). | |
82 | Very simple devices can just allocate this struct, but most of the time you | |
83 | would embed this struct inside a larger struct. | |
84 | ||
85 | You must register the device instance: | |
86 | ||
87 | v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev); | |
88 | ||
95db3a60 | 89 | Registration will initialize the v4l2_device struct. If the dev->driver_data |
2c0ab67b LP |
90 | field is NULL, it will be linked to v4l2_dev. |
91 | ||
92 | Drivers that want integration with the media device framework need to set | |
95db3a60 LP |
93 | dev->driver_data manually to point to the driver-specific device structure |
94 | that embed the struct v4l2_device instance. This is achieved by a | |
2c0ab67b LP |
95 | dev_set_drvdata() call before registering the V4L2 device instance. They must |
96 | also set the struct v4l2_device mdev field to point to a properly initialized | |
97 | and registered media_device instance. | |
95db3a60 LP |
98 | |
99 | If v4l2_dev->name is empty then it will be set to a value derived from dev | |
100 | (driver name followed by the bus_id, to be precise). If you set it up before | |
101 | calling v4l2_device_register then it will be untouched. If dev is NULL, then | |
102 | you *must* setup v4l2_dev->name before calling v4l2_device_register. | |
2a1fcdf0 | 103 | |
102e7813 HV |
104 | You can use v4l2_device_set_name() to set the name based on a driver name and |
105 | a driver-global atomic_t instance. This will generate names like ivtv0, ivtv1, | |
106 | etc. If the name ends with a digit, then it will insert a dash: cx18-0, | |
107 | cx18-1, etc. This function returns the instance number. | |
108 | ||
a47ddf14 | 109 | The first 'dev' argument is normally the struct device pointer of a pci_dev, |
073d696d | 110 | usb_interface or platform_device. It is rare for dev to be NULL, but it happens |
00575961 HV |
111 | with ISA devices or when one device creates multiple PCI devices, thus making |
112 | it impossible to associate v4l2_dev with a particular parent. | |
a47ddf14 | 113 | |
98ec6339 HV |
114 | You can also supply a notify() callback that can be called by sub-devices to |
115 | notify you of events. Whether you need to set this depends on the sub-device. | |
116 | Any notifications a sub-device supports must be defined in a header in | |
117 | include/media/<subdevice>.h. | |
118 | ||
2a1fcdf0 HV |
119 | You unregister with: |
120 | ||
121 | v4l2_device_unregister(struct v4l2_device *v4l2_dev); | |
122 | ||
95db3a60 | 123 | If the dev->driver_data field points to v4l2_dev, it will be reset to NULL. |
2a1fcdf0 HV |
124 | Unregistering will also automatically unregister all subdevs from the device. |
125 | ||
ae6cfaac HV |
126 | If you have a hotpluggable device (e.g. a USB device), then when a disconnect |
127 | happens the parent device becomes invalid. Since v4l2_device has a pointer to | |
128 | that parent device it has to be cleared as well to mark that the parent is | |
129 | gone. To do this call: | |
130 | ||
131 | v4l2_device_disconnect(struct v4l2_device *v4l2_dev); | |
132 | ||
133 | This does *not* unregister the subdevs, so you still need to call the | |
134 | v4l2_device_unregister() function for that. If your driver is not hotpluggable, | |
135 | then there is no need to call v4l2_device_disconnect(). | |
136 | ||
2a1fcdf0 HV |
137 | Sometimes you need to iterate over all devices registered by a specific |
138 | driver. This is usually the case if multiple device drivers use the same | |
139 | hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv | |
140 | hardware. The same is true for alsa drivers for example. | |
141 | ||
142 | You can iterate over all registered devices as follows: | |
143 | ||
144 | static int callback(struct device *dev, void *p) | |
145 | { | |
146 | struct v4l2_device *v4l2_dev = dev_get_drvdata(dev); | |
147 | ||
148 | /* test if this device was inited */ | |
149 | if (v4l2_dev == NULL) | |
150 | return 0; | |
151 | ... | |
152 | return 0; | |
153 | } | |
154 | ||
155 | int iterate(void *p) | |
156 | { | |
157 | struct device_driver *drv; | |
158 | int err; | |
159 | ||
160 | /* Find driver 'ivtv' on the PCI bus. | |
161 | pci_bus_type is a global. For USB busses use usb_bus_type. */ | |
162 | drv = driver_find("ivtv", &pci_bus_type); | |
163 | /* iterate over all ivtv device instances */ | |
164 | err = driver_for_each_device(drv, NULL, p, callback); | |
165 | put_driver(drv); | |
166 | return err; | |
167 | } | |
168 | ||
169 | Sometimes you need to keep a running counter of the device instance. This is | |
170 | commonly used to map a device instance to an index of a module option array. | |
171 | ||
172 | The recommended approach is as follows: | |
173 | ||
174 | static atomic_t drv_instance = ATOMIC_INIT(0); | |
175 | ||
63a29f74 | 176 | static int drv_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id) |
2a1fcdf0 HV |
177 | { |
178 | ... | |
179 | state->instance = atomic_inc_return(&drv_instance) - 1; | |
180 | } | |
181 | ||
2335e2b8 | 182 | If you have multiple device nodes then it can be difficult to know when it is |
ee71e7b3 HV |
183 | safe to unregister v4l2_device for hotpluggable devices. For this purpose |
184 | v4l2_device has refcounting support. The refcount is increased whenever | |
185 | video_register_device is called and it is decreased whenever that device node | |
186 | is released. When the refcount reaches zero, then the v4l2_device release() | |
187 | callback is called. You can do your final cleanup there. | |
2335e2b8 HV |
188 | |
189 | If other device nodes (e.g. ALSA) are created, then you can increase and | |
190 | decrease the refcount manually as well by calling: | |
191 | ||
192 | void v4l2_device_get(struct v4l2_device *v4l2_dev); | |
193 | ||
194 | or: | |
195 | ||
196 | int v4l2_device_put(struct v4l2_device *v4l2_dev); | |
2a1fcdf0 | 197 | |
ee71e7b3 HV |
198 | Since the initial refcount is 1 you also need to call v4l2_device_put in the |
199 | disconnect() callback (for USB devices) or in the remove() callback (for e.g. | |
200 | PCI devices), otherwise the refcount will never reach 0. | |
201 | ||
2a1fcdf0 HV |
202 | struct v4l2_subdev |
203 | ------------------ | |
204 | ||
205 | Many drivers need to communicate with sub-devices. These devices can do all | |
206 | sort of tasks, but most commonly they handle audio and/or video muxing, | |
207 | encoding or decoding. For webcams common sub-devices are sensors and camera | |
208 | controllers. | |
209 | ||
210 | Usually these are I2C devices, but not necessarily. In order to provide the | |
211 | driver with a consistent interface to these sub-devices the v4l2_subdev struct | |
212 | (v4l2-subdev.h) was created. | |
213 | ||
214 | Each sub-device driver must have a v4l2_subdev struct. This struct can be | |
215 | stand-alone for simple sub-devices or it might be embedded in a larger struct | |
216 | if more state information needs to be stored. Usually there is a low-level | |
217 | device struct (e.g. i2c_client) that contains the device data as setup | |
218 | by the kernel. It is recommended to store that pointer in the private | |
219 | data of v4l2_subdev using v4l2_set_subdevdata(). That makes it easy to go | |
220 | from a v4l2_subdev to the actual low-level bus-specific device data. | |
221 | ||
222 | You also need a way to go from the low-level struct to v4l2_subdev. For the | |
223 | common i2c_client struct the i2c_set_clientdata() call is used to store a | |
224 | v4l2_subdev pointer, for other busses you may have to use other methods. | |
225 | ||
692d5522 LP |
226 | Bridges might also need to store per-subdev private data, such as a pointer to |
227 | bridge-specific per-subdev private data. The v4l2_subdev structure provides | |
228 | host private data for that purpose that can be accessed with | |
229 | v4l2_get_subdev_hostdata() and v4l2_set_subdev_hostdata(). | |
230 | ||
2a1fcdf0 HV |
231 | From the bridge driver perspective you load the sub-device module and somehow |
232 | obtain the v4l2_subdev pointer. For i2c devices this is easy: you call | |
233 | i2c_get_clientdata(). For other busses something similar needs to be done. | |
234 | Helper functions exists for sub-devices on an I2C bus that do most of this | |
235 | tricky work for you. | |
236 | ||
237 | Each v4l2_subdev contains function pointers that sub-device drivers can | |
238 | implement (or leave NULL if it is not applicable). Since sub-devices can do | |
239 | so many different things and you do not want to end up with a huge ops struct | |
240 | of which only a handful of ops are commonly implemented, the function pointers | |
241 | are sorted according to category and each category has its own ops struct. | |
242 | ||
243 | The top-level ops struct contains pointers to the category ops structs, which | |
244 | may be NULL if the subdev driver does not support anything from that category. | |
245 | ||
246 | It looks like this: | |
247 | ||
248 | struct v4l2_subdev_core_ops { | |
2a1fcdf0 HV |
249 | int (*log_status)(struct v4l2_subdev *sd); |
250 | int (*init)(struct v4l2_subdev *sd, u32 val); | |
251 | ... | |
252 | }; | |
253 | ||
254 | struct v4l2_subdev_tuner_ops { | |
255 | ... | |
256 | }; | |
257 | ||
258 | struct v4l2_subdev_audio_ops { | |
259 | ... | |
260 | }; | |
261 | ||
262 | struct v4l2_subdev_video_ops { | |
263 | ... | |
264 | }; | |
265 | ||
48398f93 SA |
266 | struct v4l2_subdev_pad_ops { |
267 | ... | |
268 | }; | |
269 | ||
2a1fcdf0 HV |
270 | struct v4l2_subdev_ops { |
271 | const struct v4l2_subdev_core_ops *core; | |
272 | const struct v4l2_subdev_tuner_ops *tuner; | |
273 | const struct v4l2_subdev_audio_ops *audio; | |
274 | const struct v4l2_subdev_video_ops *video; | |
48398f93 | 275 | const struct v4l2_subdev_pad_ops *video; |
2a1fcdf0 HV |
276 | }; |
277 | ||
278 | The core ops are common to all subdevs, the other categories are implemented | |
279 | depending on the sub-device. E.g. a video device is unlikely to support the | |
280 | audio ops and vice versa. | |
281 | ||
282 | This setup limits the number of function pointers while still making it easy | |
283 | to add new ops and categories. | |
284 | ||
285 | A sub-device driver initializes the v4l2_subdev struct using: | |
286 | ||
89aec3e1 | 287 | v4l2_subdev_init(sd, &ops); |
2a1fcdf0 HV |
288 | |
289 | Afterwards you need to initialize subdev->name with a unique name and set the | |
290 | module owner. This is done for you if you use the i2c helper functions. | |
291 | ||
61f5db54 LP |
292 | If integration with the media framework is needed, you must initialize the |
293 | media_entity struct embedded in the v4l2_subdev struct (entity field) by | |
294 | calling media_entity_init(): | |
295 | ||
296 | struct media_pad *pads = &my_sd->pads; | |
297 | int err; | |
298 | ||
299 | err = media_entity_init(&sd->entity, npads, pads, 0); | |
300 | ||
301 | The pads array must have been previously initialized. There is no need to | |
302 | manually set the struct media_entity type and name fields, but the revision | |
303 | field must be initialized if needed. | |
304 | ||
305 | A reference to the entity will be automatically acquired/released when the | |
306 | subdev device node (if any) is opened/closed. | |
307 | ||
308 | Don't forget to cleanup the media entity before the sub-device is destroyed: | |
309 | ||
310 | media_entity_cleanup(&sd->entity); | |
311 | ||
48398f93 SA |
312 | If the subdev driver intends to process video and integrate with the media |
313 | framework, it must implement format related functionality using | |
314 | v4l2_subdev_pad_ops instead of v4l2_subdev_video_ops. | |
315 | ||
8227c92b SA |
316 | In that case, the subdev driver may set the link_validate field to provide |
317 | its own link validation function. The link validation function is called for | |
318 | every link in the pipeline where both of the ends of the links are V4L2 | |
319 | sub-devices. The driver is still responsible for validating the correctness | |
320 | of the format configuration between sub-devices and video nodes. | |
321 | ||
322 | If link_validate op is not set, the default function | |
323 | v4l2_subdev_link_validate_default() is used instead. This function ensures | |
324 | that width, height and the media bus pixel code are equal on both source and | |
325 | sink of the link. Subdev drivers are also free to use this function to | |
326 | perform the checks mentioned above in addition to their own checks. | |
327 | ||
c67f1a30 GL |
328 | There are currently two ways to register subdevices with the V4L2 core. The |
329 | first (traditional) possibility is to have subdevices registered by bridge | |
330 | drivers. This can be done when the bridge driver has the complete information | |
331 | about subdevices connected to it and knows exactly when to register them. This | |
332 | is typically the case for internal subdevices, like video data processing units | |
333 | within SoCs or complex PCI(e) boards, camera sensors in USB cameras or connected | |
334 | to SoCs, which pass information about them to bridge drivers, usually in their | |
335 | platform data. | |
336 | ||
337 | There are however also situations where subdevices have to be registered | |
338 | asynchronously to bridge devices. An example of such a configuration is a Device | |
339 | Tree based system where information about subdevices is made available to the | |
340 | system independently from the bridge devices, e.g. when subdevices are defined | |
341 | in DT as I2C device nodes. The API used in this second case is described further | |
342 | below. | |
343 | ||
344 | Using one or the other registration method only affects the probing process, the | |
345 | run-time bridge-subdevice interaction is in both cases the same. | |
346 | ||
347 | In the synchronous case a device (bridge) driver needs to register the | |
348 | v4l2_subdev with the v4l2_device: | |
2a1fcdf0 | 349 | |
89aec3e1 | 350 | int err = v4l2_device_register_subdev(v4l2_dev, sd); |
2a1fcdf0 HV |
351 | |
352 | This can fail if the subdev module disappeared before it could be registered. | |
353 | After this function was called successfully the subdev->dev field points to | |
354 | the v4l2_device. | |
355 | ||
61f5db54 LP |
356 | If the v4l2_device parent device has a non-NULL mdev field, the sub-device |
357 | entity will be automatically registered with the media device. | |
358 | ||
2a1fcdf0 HV |
359 | You can unregister a sub-device using: |
360 | ||
89aec3e1 | 361 | v4l2_device_unregister_subdev(sd); |
2a1fcdf0 | 362 | |
89aec3e1 | 363 | Afterwards the subdev module can be unloaded and sd->dev == NULL. |
2a1fcdf0 HV |
364 | |
365 | You can call an ops function either directly: | |
366 | ||
2249aa5c | 367 | err = sd->ops->core->g_std(sd, &norm); |
2a1fcdf0 HV |
368 | |
369 | but it is better and easier to use this macro: | |
370 | ||
2249aa5c | 371 | err = v4l2_subdev_call(sd, core, g_std, &norm); |
2a1fcdf0 HV |
372 | |
373 | The macro will to the right NULL pointer checks and returns -ENODEV if subdev | |
2249aa5c HV |
374 | is NULL, -ENOIOCTLCMD if either subdev->core or subdev->core->g_std is |
375 | NULL, or the actual result of the subdev->ops->core->g_std ops. | |
2a1fcdf0 HV |
376 | |
377 | It is also possible to call all or a subset of the sub-devices: | |
378 | ||
2249aa5c | 379 | v4l2_device_call_all(v4l2_dev, 0, core, g_std, &norm); |
2a1fcdf0 HV |
380 | |
381 | Any subdev that does not support this ops is skipped and error results are | |
382 | ignored. If you want to check for errors use this: | |
383 | ||
2249aa5c | 384 | err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_std, &norm); |
2a1fcdf0 HV |
385 | |
386 | Any error except -ENOIOCTLCMD will exit the loop with that error. If no | |
25985edc | 387 | errors (except -ENOIOCTLCMD) occurred, then 0 is returned. |
2a1fcdf0 HV |
388 | |
389 | The second argument to both calls is a group ID. If 0, then all subdevs are | |
390 | called. If non-zero, then only those whose group ID match that value will | |
b0167600 | 391 | be called. Before a bridge driver registers a subdev it can set sd->grp_id |
2a1fcdf0 HV |
392 | to whatever value it wants (it's 0 by default). This value is owned by the |
393 | bridge driver and the sub-device driver will never modify or use it. | |
394 | ||
395 | The group ID gives the bridge driver more control how callbacks are called. | |
396 | For example, there may be multiple audio chips on a board, each capable of | |
397 | changing the volume. But usually only one will actually be used when the | |
398 | user want to change the volume. You can set the group ID for that subdev to | |
399 | e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling | |
400 | v4l2_device_call_all(). That ensures that it will only go to the subdev | |
401 | that needs it. | |
402 | ||
98ec6339 HV |
403 | If the sub-device needs to notify its v4l2_device parent of an event, then |
404 | it can call v4l2_subdev_notify(sd, notification, arg). This macro checks | |
405 | whether there is a notify() callback defined and returns -ENODEV if not. | |
406 | Otherwise the result of the notify() call is returned. | |
407 | ||
2a1fcdf0 HV |
408 | The advantage of using v4l2_subdev is that it is a generic struct and does |
409 | not contain any knowledge about the underlying hardware. So a driver might | |
410 | contain several subdevs that use an I2C bus, but also a subdev that is | |
411 | controlled through GPIO pins. This distinction is only relevant when setting | |
412 | up the device, but once the subdev is registered it is completely transparent. | |
413 | ||
414 | ||
c67f1a30 GL |
415 | In the asynchronous case subdevice probing can be invoked independently of the |
416 | bridge driver availability. The subdevice driver then has to verify whether all | |
417 | the requirements for a successful probing are satisfied. This can include a | |
418 | check for a master clock availability. If any of the conditions aren't satisfied | |
419 | the driver might decide to return -EPROBE_DEFER to request further reprobing | |
420 | attempts. Once all conditions are met the subdevice shall be registered using | |
421 | the v4l2_async_register_subdev() function. Unregistration is performed using | |
422 | the v4l2_async_unregister_subdev() call. Subdevices registered this way are | |
423 | stored in a global list of subdevices, ready to be picked up by bridge drivers. | |
424 | ||
425 | Bridge drivers in turn have to register a notifier object with an array of | |
426 | subdevice descriptors that the bridge device needs for its operation. This is | |
427 | performed using the v4l2_async_notifier_register() call. To unregister the | |
428 | notifier the driver has to call v4l2_async_notifier_unregister(). The former of | |
429 | the two functions takes two arguments: a pointer to struct v4l2_device and a | |
430 | pointer to struct v4l2_async_notifier. The latter contains a pointer to an array | |
431 | of pointers to subdevice descriptors of type struct v4l2_async_subdev type. The | |
432 | V4L2 core will then use these descriptors to match asynchronously registered | |
433 | subdevices to them. If a match is detected the .bound() notifier callback is | |
434 | called. After all subdevices have been located the .complete() callback is | |
435 | called. When a subdevice is removed from the system the .unbind() method is | |
436 | called. All three callbacks are optional. | |
437 | ||
438 | ||
2096a5dc LP |
439 | V4L2 sub-device userspace API |
440 | ----------------------------- | |
441 | ||
442 | Beside exposing a kernel API through the v4l2_subdev_ops structure, V4L2 | |
443 | sub-devices can also be controlled directly by userspace applications. | |
444 | ||
445 | Device nodes named v4l-subdevX can be created in /dev to access sub-devices | |
446 | directly. If a sub-device supports direct userspace configuration it must set | |
447 | the V4L2_SUBDEV_FL_HAS_DEVNODE flag before being registered. | |
448 | ||
449 | After registering sub-devices, the v4l2_device driver can create device nodes | |
450 | for all registered sub-devices marked with V4L2_SUBDEV_FL_HAS_DEVNODE by calling | |
451 | v4l2_device_register_subdev_nodes(). Those device nodes will be automatically | |
452 | removed when sub-devices are unregistered. | |
453 | ||
ea8aa434 LP |
454 | The device node handles a subset of the V4L2 API. |
455 | ||
456 | VIDIOC_QUERYCTRL | |
457 | VIDIOC_QUERYMENU | |
458 | VIDIOC_G_CTRL | |
459 | VIDIOC_S_CTRL | |
460 | VIDIOC_G_EXT_CTRLS | |
461 | VIDIOC_S_EXT_CTRLS | |
462 | VIDIOC_TRY_EXT_CTRLS | |
463 | ||
464 | The controls ioctls are identical to the ones defined in V4L2. They | |
465 | behave identically, with the only exception that they deal only with | |
466 | controls implemented in the sub-device. Depending on the driver, those | |
467 | controls can be also be accessed through one (or several) V4L2 device | |
468 | nodes. | |
469 | ||
02adb1cc SA |
470 | VIDIOC_DQEVENT |
471 | VIDIOC_SUBSCRIBE_EVENT | |
472 | VIDIOC_UNSUBSCRIBE_EVENT | |
473 | ||
474 | The events ioctls are identical to the ones defined in V4L2. They | |
475 | behave identically, with the only exception that they deal only with | |
476 | events generated by the sub-device. Depending on the driver, those | |
477 | events can also be reported by one (or several) V4L2 device nodes. | |
478 | ||
479 | Sub-device drivers that want to use events need to set the | |
480 | V4L2_SUBDEV_USES_EVENTS v4l2_subdev::flags and initialize | |
481 | v4l2_subdev::nevents to events queue depth before registering the | |
482 | sub-device. After registration events can be queued as usual on the | |
483 | v4l2_subdev::devnode device node. | |
484 | ||
485 | To properly support events, the poll() file operation is also | |
486 | implemented. | |
487 | ||
c30b46e5 LP |
488 | Private ioctls |
489 | ||
490 | All ioctls not in the above list are passed directly to the sub-device | |
491 | driver through the core::ioctl operation. | |
492 | ||
2096a5dc | 493 | |
2a1fcdf0 HV |
494 | I2C sub-device drivers |
495 | ---------------------- | |
496 | ||
497 | Since these drivers are so common, special helper functions are available to | |
498 | ease the use of these drivers (v4l2-common.h). | |
499 | ||
500 | The recommended method of adding v4l2_subdev support to an I2C driver is to | |
501 | embed the v4l2_subdev struct into the state struct that is created for each | |
502 | I2C device instance. Very simple devices have no state struct and in that case | |
503 | you can just create a v4l2_subdev directly. | |
504 | ||
505 | A typical state struct would look like this (where 'chipname' is replaced by | |
506 | the name of the chip): | |
507 | ||
508 | struct chipname_state { | |
509 | struct v4l2_subdev sd; | |
510 | ... /* additional state fields */ | |
511 | }; | |
512 | ||
513 | Initialize the v4l2_subdev struct as follows: | |
514 | ||
515 | v4l2_i2c_subdev_init(&state->sd, client, subdev_ops); | |
516 | ||
517 | This function will fill in all the fields of v4l2_subdev and ensure that the | |
518 | v4l2_subdev and i2c_client both point to one another. | |
519 | ||
520 | You should also add a helper inline function to go from a v4l2_subdev pointer | |
521 | to a chipname_state struct: | |
522 | ||
523 | static inline struct chipname_state *to_state(struct v4l2_subdev *sd) | |
524 | { | |
525 | return container_of(sd, struct chipname_state, sd); | |
526 | } | |
527 | ||
528 | Use this to go from the v4l2_subdev struct to the i2c_client struct: | |
529 | ||
530 | struct i2c_client *client = v4l2_get_subdevdata(sd); | |
531 | ||
532 | And this to go from an i2c_client to a v4l2_subdev struct: | |
533 | ||
534 | struct v4l2_subdev *sd = i2c_get_clientdata(client); | |
535 | ||
2a1fcdf0 HV |
536 | Make sure to call v4l2_device_unregister_subdev(sd) when the remove() callback |
537 | is called. This will unregister the sub-device from the bridge driver. It is | |
538 | safe to call this even if the sub-device was never registered. | |
539 | ||
f5360bdc HV |
540 | You need to do this because when the bridge driver destroys the i2c adapter |
541 | the remove() callbacks are called of the i2c devices on that adapter. | |
542 | After that the corresponding v4l2_subdev structures are invalid, so they | |
543 | have to be unregistered first. Calling v4l2_device_unregister_subdev(sd) | |
544 | from the remove() callback ensures that this is always done correctly. | |
545 | ||
2a1fcdf0 HV |
546 | |
547 | The bridge driver also has some helper functions it can use: | |
548 | ||
e6574f2f | 549 | struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter, |
53dacb15 | 550 | "module_foo", "chipid", 0x36, NULL); |
2a1fcdf0 HV |
551 | |
552 | This loads the given module (can be NULL if no module needs to be loaded) and | |
553 | calls i2c_new_device() with the given i2c_adapter and chip/address arguments. | |
e6574f2f | 554 | If all goes well, then it registers the subdev with the v4l2_device. |
2a1fcdf0 | 555 | |
53dacb15 HV |
556 | You can also use the last argument of v4l2_i2c_new_subdev() to pass an array |
557 | of possible I2C addresses that it should probe. These probe addresses are | |
558 | only used if the previous argument is 0. A non-zero argument means that you | |
559 | know the exact i2c address so in that case no probing will take place. | |
2a1fcdf0 HV |
560 | |
561 | Both functions return NULL if something went wrong. | |
562 | ||
53dacb15 | 563 | Note that the chipid you pass to v4l2_i2c_new_subdev() is usually |
2c792523 HV |
564 | the same as the module name. It allows you to specify a chip variant, e.g. |
565 | "saa7114" or "saa7115". In general though the i2c driver autodetects this. | |
566 | The use of chipid is something that needs to be looked at more closely at a | |
567 | later date. It differs between i2c drivers and as such can be confusing. | |
568 | To see which chip variants are supported you can look in the i2c driver code | |
569 | for the i2c_device_id table. This lists all the possibilities. | |
570 | ||
2c0b19ac HV |
571 | There are two more helper functions: |
572 | ||
573 | v4l2_i2c_new_subdev_cfg: this function adds new irq and platform_data | |
574 | arguments and has both 'addr' and 'probed_addrs' arguments: if addr is not | |
575 | 0 then that will be used (non-probing variant), otherwise the probed_addrs | |
576 | are probed. | |
577 | ||
578 | For example: this will probe for address 0x10: | |
579 | ||
580 | struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter, | |
581 | "module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10)); | |
582 | ||
583 | v4l2_i2c_new_subdev_board uses an i2c_board_info struct which is passed | |
584 | to the i2c driver and replaces the irq, platform_data and addr arguments. | |
585 | ||
586 | If the subdev supports the s_config core ops, then that op is called with | |
587 | the irq and platform_data arguments after the subdev was setup. The older | |
588 | v4l2_i2c_new_(probed_)subdev functions will call s_config as well, but with | |
589 | irq set to 0 and platform_data set to NULL. | |
590 | ||
2a1fcdf0 HV |
591 | struct video_device |
592 | ------------------- | |
593 | ||
a47ddf14 HV |
594 | The actual device nodes in the /dev directory are created using the |
595 | video_device struct (v4l2-dev.h). This struct can either be allocated | |
596 | dynamically or embedded in a larger struct. | |
597 | ||
598 | To allocate it dynamically use: | |
599 | ||
600 | struct video_device *vdev = video_device_alloc(); | |
601 | ||
602 | if (vdev == NULL) | |
603 | return -ENOMEM; | |
604 | ||
605 | vdev->release = video_device_release; | |
606 | ||
607 | If you embed it in a larger struct, then you must set the release() | |
608 | callback to your own function: | |
609 | ||
610 | struct video_device *vdev = &my_vdev->vdev; | |
611 | ||
612 | vdev->release = my_vdev_release; | |
613 | ||
614 | The release callback must be set and it is called when the last user | |
615 | of the video device exits. | |
616 | ||
617 | The default video_device_release() callback just calls kfree to free the | |
618 | allocated memory. | |
619 | ||
7cb59509 HV |
620 | There is also a video_device_release_empty() function that does nothing |
621 | (is empty) and can be used if the struct is embedded and there is nothing | |
622 | to do when it is released. | |
623 | ||
a47ddf14 HV |
624 | You should also set these fields: |
625 | ||
7cb59509 | 626 | - v4l2_dev: must be set to the v4l2_device parent device. |
8ab75e3e | 627 | |
a47ddf14 | 628 | - name: set to something descriptive and unique. |
8ab75e3e | 629 | |
d2210f9e HV |
630 | - vfl_dir: set this to VFL_DIR_RX for capture devices (VFL_DIR_RX has value 0, |
631 | so this is normally already the default), set to VFL_DIR_TX for output | |
632 | devices and VFL_DIR_M2M for mem2mem (codec) devices. | |
633 | ||
c7dd09da | 634 | - fops: set to the v4l2_file_operations struct. |
8ab75e3e | 635 | |
a47ddf14 HV |
636 | - ioctl_ops: if you use the v4l2_ioctl_ops to simplify ioctl maintenance |
637 | (highly recommended to use this and it might become compulsory in the | |
d2210f9e HV |
638 | future!), then set this to your v4l2_ioctl_ops struct. The vfl_type and |
639 | vfl_dir fields are used to disable ops that do not match the type/dir | |
640 | combination. E.g. VBI ops are disabled for non-VBI nodes, and output ops | |
641 | are disabled for a capture device. This makes it possible to provide | |
642 | just one v4l2_ioctl_ops struct for both vbi and video nodes. | |
8ab75e3e | 643 | |
ee6869af | 644 | - lock: leave to NULL if you want to do all the locking in the driver. |
74f22c48 HV |
645 | Otherwise you give it a pointer to a struct mutex_lock and before the |
646 | unlocked_ioctl file operation is called this lock will be taken by the | |
8ab75e3e HV |
647 | core and released afterwards. See the next section for more details. |
648 | ||
4a77a836 HV |
649 | - queue: a pointer to the struct vb2_queue associated with this device node. |
650 | If queue is non-NULL, and queue->lock is non-NULL, then queue->lock is | |
651 | used for the queuing ioctls (VIDIOC_REQBUFS, CREATE_BUFS, QBUF, DQBUF, | |
652 | QUERYBUF, PREPARE_BUF, STREAMON and STREAMOFF) instead of the lock above. | |
653 | That way the vb2 queuing framework does not have to wait for other ioctls. | |
654 | This queue pointer is also used by the vb2 helper functions to check for | |
655 | queuing ownership (i.e. is the filehandle calling it allowed to do the | |
656 | operation). | |
657 | ||
6e29ad50 HV |
658 | - prio: keeps track of the priorities. Used to implement VIDIOC_G/S_PRIORITY. |
659 | If left to NULL, then it will use the struct v4l2_prio_state in v4l2_device. | |
660 | If you want to have a separate priority state per (group of) device node(s), | |
661 | then you can point it to your own struct v4l2_prio_state. | |
8ab75e3e | 662 | |
7cb59509 | 663 | - dev_parent: you only set this if v4l2_device was registered with NULL as |
00575961 HV |
664 | the parent device struct. This only happens in cases where one hardware |
665 | device has multiple PCI devices that all share the same v4l2_device core. | |
666 | ||
667 | The cx88 driver is an example of this: one core v4l2_device struct, but | |
7cb59509 HV |
668 | it is used by both a raw video PCI device (cx8800) and a MPEG PCI device |
669 | (cx8802). Since the v4l2_device cannot be associated with two PCI devices | |
670 | at the same time it is setup without a parent device. But when the struct | |
671 | video_device is initialized you *do* know which parent PCI device to use and | |
672 | so you set dev_device to the correct PCI device. | |
8ab75e3e | 673 | |
b1a873a3 HV |
674 | - flags: optional. Set to V4L2_FL_USE_FH_PRIO if you want to let the framework |
675 | handle the VIDIOC_G/S_PRIORITY ioctls. This requires that you use struct | |
676 | v4l2_fh. Eventually this flag will disappear once all drivers use the core | |
677 | priority handling. But for now it has to be set explicitly. | |
a47ddf14 | 678 | |
6e29ad50 HV |
679 | If you use v4l2_ioctl_ops, then you should set .unlocked_ioctl to video_ioctl2 |
680 | in your v4l2_file_operations struct. | |
681 | ||
682 | Do not use .ioctl! This is deprecated and will go away in the future. | |
c7dd09da | 683 | |
1dd8728e HV |
684 | In some cases you want to tell the core that a function you had specified in |
685 | your v4l2_ioctl_ops should be ignored. You can mark such ioctls by calling this | |
686 | function before video_device_register is called: | |
687 | ||
152a3a73 | 688 | void v4l2_disable_ioctl(struct video_device *vdev, unsigned int cmd); |
1dd8728e HV |
689 | |
690 | This tends to be needed if based on external factors (e.g. which card is | |
691 | being used) you want to turns off certain features in v4l2_ioctl_ops without | |
692 | having to make a new struct. | |
693 | ||
c7dd09da HV |
694 | The v4l2_file_operations struct is a subset of file_operations. The main |
695 | difference is that the inode argument is omitted since it is never used. | |
a47ddf14 | 696 | |
2c0ab67b LP |
697 | If integration with the media framework is needed, you must initialize the |
698 | media_entity struct embedded in the video_device struct (entity field) by | |
699 | calling media_entity_init(): | |
700 | ||
701 | struct media_pad *pad = &my_vdev->pad; | |
702 | int err; | |
703 | ||
704 | err = media_entity_init(&vdev->entity, 1, pad, 0); | |
705 | ||
706 | The pads array must have been previously initialized. There is no need to | |
707 | manually set the struct media_entity type and name fields. | |
708 | ||
709 | A reference to the entity will be automatically acquired/released when the | |
710 | video device is opened/closed. | |
711 | ||
4a77a836 HV |
712 | ioctls and locking |
713 | ------------------ | |
8ab75e3e | 714 | |
4a77a836 HV |
715 | The V4L core provides optional locking services. The main service is the |
716 | lock field in struct video_device, which is a pointer to a mutex. If you set | |
717 | this pointer, then that will be used by unlocked_ioctl to serialize all ioctls. | |
8ab75e3e | 718 | |
4a77a836 HV |
719 | If you are using the videobuf2 framework, then there is a second lock that you |
720 | can set: video_device->queue->lock. If set, then this lock will be used instead | |
721 | of video_device->lock to serialize all queuing ioctls (see the previous section | |
722 | for the full list of those ioctls). | |
8ab75e3e | 723 | |
4a77a836 HV |
724 | The advantage of using a different lock for the queuing ioctls is that for some |
725 | drivers (particularly USB drivers) certain commands such as setting controls | |
726 | can take a long time, so you want to use a separate lock for the buffer queuing | |
727 | ioctls. That way your VIDIOC_DQBUF doesn't stall because the driver is busy | |
728 | changing the e.g. exposure of the webcam. | |
ee6869af | 729 | |
4a77a836 HV |
730 | Of course, you can always do all the locking yourself by leaving both lock |
731 | pointers at NULL. | |
43599f31 | 732 | |
4a77a836 HV |
733 | If you use the old videobuf then you must pass the video_device lock to the |
734 | videobuf queue initialize function: if videobuf has to wait for a frame to | |
735 | arrive, then it will temporarily unlock the lock and relock it afterwards. If | |
736 | your driver also waits in the code, then you should do the same to allow other | |
737 | processes to access the device node while the first process is waiting for | |
738 | something. | |
ee6869af | 739 | |
43599f31 | 740 | In the case of videobuf2 you will need to implement the wait_prepare and |
4a77a836 HV |
741 | wait_finish callbacks to unlock/lock if applicable. If you use the queue->lock |
742 | pointer, then you can use the helper functions vb2_ops_wait_prepare/finish. | |
743 | ||
744 | The implementation of a hotplug disconnect should also take the lock from | |
745 | video_device before calling v4l2_device_disconnect. If you are also using | |
746 | video_device->queue->lock, then you have to first lock video_device->queue->lock | |
747 | followed by video_device->lock. That way you can be sure no ioctl is running | |
748 | when you call v4l2_device_disconnect. | |
a47ddf14 HV |
749 | |
750 | video_device registration | |
751 | ------------------------- | |
752 | ||
753 | Next you register the video device: this will create the character device | |
754 | for you. | |
755 | ||
756 | err = video_register_device(vdev, VFL_TYPE_GRABBER, -1); | |
757 | if (err) { | |
50a2a8b3 | 758 | video_device_release(vdev); /* or kfree(my_vdev); */ |
a47ddf14 HV |
759 | return err; |
760 | } | |
761 | ||
2c0ab67b LP |
762 | If the v4l2_device parent device has a non-NULL mdev field, the video device |
763 | entity will be automatically registered with the media device. | |
764 | ||
a47ddf14 HV |
765 | Which device is registered depends on the type argument. The following |
766 | types exist: | |
767 | ||
768 | VFL_TYPE_GRABBER: videoX for video input/output devices | |
769 | VFL_TYPE_VBI: vbiX for vertical blank data (i.e. closed captions, teletext) | |
770 | VFL_TYPE_RADIO: radioX for radio tuners | |
a47ddf14 HV |
771 | |
772 | The last argument gives you a certain amount of control over the device | |
6b5270d2 HV |
773 | device node number used (i.e. the X in videoX). Normally you will pass -1 |
774 | to let the v4l2 framework pick the first free number. But sometimes users | |
775 | want to select a specific node number. It is common that drivers allow | |
776 | the user to select a specific device node number through a driver module | |
777 | option. That number is then passed to this function and video_register_device | |
778 | will attempt to select that device node number. If that number was already | |
779 | in use, then the next free device node number will be selected and it | |
780 | will send a warning to the kernel log. | |
781 | ||
782 | Another use-case is if a driver creates many devices. In that case it can | |
783 | be useful to place different video devices in separate ranges. For example, | |
784 | video capture devices start at 0, video output devices start at 16. | |
22e22125 HV |
785 | So you can use the last argument to specify a minimum device node number |
786 | and the v4l2 framework will try to pick the first free number that is equal | |
a47ddf14 HV |
787 | or higher to what you passed. If that fails, then it will just pick the |
788 | first free number. | |
789 | ||
6b5270d2 HV |
790 | Since in this case you do not care about a warning about not being able |
791 | to select the specified device node number, you can call the function | |
792 | video_register_device_no_warn() instead. | |
793 | ||
a47ddf14 HV |
794 | Whenever a device node is created some attributes are also created for you. |
795 | If you look in /sys/class/video4linux you see the devices. Go into e.g. | |
796 | video0 and you will see 'name' and 'index' attributes. The 'name' attribute | |
7ae0cd9b | 797 | is the 'name' field of the video_device struct. |
a47ddf14 | 798 | |
7ae0cd9b HV |
799 | The 'index' attribute is the index of the device node: for each call to |
800 | video_register_device() the index is just increased by 1. The first video | |
801 | device node you register always starts with index 0. | |
a47ddf14 HV |
802 | |
803 | Users can setup udev rules that utilize the index attribute to make fancy | |
804 | device names (e.g. 'mpegX' for MPEG video capture device nodes). | |
805 | ||
806 | After the device was successfully registered, then you can use these fields: | |
807 | ||
808 | - vfl_type: the device type passed to video_register_device. | |
809 | - minor: the assigned device minor number. | |
22e22125 | 810 | - num: the device node number (i.e. the X in videoX). |
7ae0cd9b | 811 | - index: the device index number. |
a47ddf14 HV |
812 | |
813 | If the registration failed, then you need to call video_device_release() | |
814 | to free the allocated video_device struct, or free your own struct if the | |
815 | video_device was embedded in it. The vdev->release() callback will never | |
816 | be called if the registration failed, nor should you ever attempt to | |
817 | unregister the device if the registration failed. | |
818 | ||
819 | ||
820 | video_device cleanup | |
821 | -------------------- | |
822 | ||
823 | When the video device nodes have to be removed, either during the unload | |
824 | of the driver or because the USB device was disconnected, then you should | |
825 | unregister them: | |
826 | ||
827 | video_unregister_device(vdev); | |
828 | ||
829 | This will remove the device nodes from sysfs (causing udev to remove them | |
830 | from /dev). | |
831 | ||
dd1ad942 HV |
832 | After video_unregister_device() returns no new opens can be done. However, |
833 | in the case of USB devices some application might still have one of these | |
d69f2718 HV |
834 | device nodes open. So after the unregister all file operations (except |
835 | release, of course) will return an error as well. | |
a47ddf14 HV |
836 | |
837 | When the last user of the video device node exits, then the vdev->release() | |
838 | callback is called and you can do the final cleanup there. | |
839 | ||
2c0ab67b LP |
840 | Don't forget to cleanup the media entity associated with the video device if |
841 | it has been initialized: | |
842 | ||
843 | media_entity_cleanup(&vdev->entity); | |
844 | ||
845 | This can be done from the release callback. | |
846 | ||
a47ddf14 HV |
847 | |
848 | video_device helper functions | |
849 | ----------------------------- | |
850 | ||
851 | There are a few useful helper functions: | |
852 | ||
eac8ea53 LP |
853 | - file/video_device private data |
854 | ||
a47ddf14 HV |
855 | You can set/get driver private data in the video_device struct using: |
856 | ||
89aec3e1 HV |
857 | void *video_get_drvdata(struct video_device *vdev); |
858 | void video_set_drvdata(struct video_device *vdev, void *data); | |
a47ddf14 HV |
859 | |
860 | Note that you can safely call video_set_drvdata() before calling | |
861 | video_register_device(). | |
862 | ||
863 | And this function: | |
864 | ||
865 | struct video_device *video_devdata(struct file *file); | |
866 | ||
867 | returns the video_device belonging to the file struct. | |
868 | ||
eac8ea53 | 869 | The video_drvdata function combines video_get_drvdata with video_devdata: |
a47ddf14 HV |
870 | |
871 | void *video_drvdata(struct file *file); | |
872 | ||
873 | You can go from a video_device struct to the v4l2_device struct using: | |
874 | ||
dfa9a5ae | 875 | struct v4l2_device *v4l2_dev = vdev->v4l2_dev; |
44061c05 | 876 | |
eac8ea53 LP |
877 | - Device node name |
878 | ||
879 | The video_device node kernel name can be retrieved using | |
880 | ||
881 | const char *video_device_node_name(struct video_device *vdev); | |
882 | ||
883 | The name is used as a hint by userspace tools such as udev. The function | |
884 | should be used where possible instead of accessing the video_device::num and | |
885 | video_device::minor fields. | |
886 | ||
887 | ||
44061c05 MCC |
888 | video buffer helper functions |
889 | ----------------------------- | |
890 | ||
4b586a38 JC |
891 | The v4l2 core API provides a set of standard methods (called "videobuf") |
892 | for dealing with video buffers. Those methods allow a driver to implement | |
893 | read(), mmap() and overlay() in a consistent way. There are currently | |
894 | methods for using video buffers on devices that supports DMA with | |
895 | scatter/gather method (videobuf-dma-sg), DMA with linear access | |
896 | (videobuf-dma-contig), and vmalloced buffers, mostly used on USB drivers | |
897 | (videobuf-vmalloc). | |
898 | ||
899 | Please see Documentation/video4linux/videobuf for more information on how | |
900 | to use the videobuf layer. | |
6cd84b78 SA |
901 | |
902 | struct v4l2_fh | |
903 | -------------- | |
904 | ||
905 | struct v4l2_fh provides a way to easily keep file handle specific data | |
6e29ad50 | 906 | that is used by the V4L2 framework. New drivers must use struct v4l2_fh |
b1a873a3 HV |
907 | since it is also used to implement priority handling (VIDIOC_G/S_PRIORITY) |
908 | if the video_device flag V4L2_FL_USE_FH_PRIO is also set. | |
6cd84b78 SA |
909 | |
910 | The users of v4l2_fh (in the V4L2 framework, not the driver) know | |
911 | whether a driver uses v4l2_fh as its file->private_data pointer by | |
6e29ad50 HV |
912 | testing the V4L2_FL_USES_V4L2_FH bit in video_device->flags. This bit is |
913 | set whenever v4l2_fh_init() is called. | |
6cd84b78 | 914 | |
6e29ad50 HV |
915 | struct v4l2_fh is allocated as a part of the driver's own file handle |
916 | structure and file->private_data is set to it in the driver's open | |
917 | function by the driver. | |
6cd84b78 | 918 | |
6e29ad50 HV |
919 | In many cases the struct v4l2_fh will be embedded in a larger structure. |
920 | In that case you should call v4l2_fh_init+v4l2_fh_add in open() and | |
921 | v4l2_fh_del+v4l2_fh_exit in release(). | |
6cd84b78 | 922 | |
6e29ad50 HV |
923 | Drivers can extract their own file handle structure by using the container_of |
924 | macro. Example: | |
6cd84b78 SA |
925 | |
926 | struct my_fh { | |
927 | int blah; | |
928 | struct v4l2_fh fh; | |
929 | }; | |
930 | ||
931 | ... | |
932 | ||
933 | int my_open(struct file *file) | |
934 | { | |
935 | struct my_fh *my_fh; | |
936 | struct video_device *vfd; | |
937 | int ret; | |
938 | ||
939 | ... | |
940 | ||
6e29ad50 HV |
941 | my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL); |
942 | ||
943 | ... | |
944 | ||
98019f5e | 945 | v4l2_fh_init(&my_fh->fh, vfd); |
6cd84b78 | 946 | |
6e29ad50 | 947 | ... |
6cd84b78 SA |
948 | |
949 | file->private_data = &my_fh->fh; | |
6e29ad50 HV |
950 | v4l2_fh_add(&my_fh->fh); |
951 | return 0; | |
6cd84b78 SA |
952 | } |
953 | ||
954 | int my_release(struct file *file) | |
955 | { | |
956 | struct v4l2_fh *fh = file->private_data; | |
957 | struct my_fh *my_fh = container_of(fh, struct my_fh, fh); | |
958 | ||
959 | ... | |
6e29ad50 HV |
960 | v4l2_fh_del(&my_fh->fh); |
961 | v4l2_fh_exit(&my_fh->fh); | |
962 | kfree(my_fh); | |
963 | return 0; | |
6cd84b78 | 964 | } |
dd966083 | 965 | |
6e29ad50 HV |
966 | Below is a short description of the v4l2_fh functions used: |
967 | ||
98019f5e | 968 | void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev) |
6e29ad50 HV |
969 | |
970 | Initialise the file handle. This *MUST* be performed in the driver's | |
971 | v4l2_file_operations->open() handler. | |
972 | ||
973 | void v4l2_fh_add(struct v4l2_fh *fh) | |
974 | ||
975 | Add a v4l2_fh to video_device file handle list. Must be called once the | |
976 | file handle is completely initialized. | |
977 | ||
978 | void v4l2_fh_del(struct v4l2_fh *fh) | |
979 | ||
980 | Unassociate the file handle from video_device(). The file handle | |
981 | exit function may now be called. | |
982 | ||
983 | void v4l2_fh_exit(struct v4l2_fh *fh) | |
984 | ||
985 | Uninitialise the file handle. After uninitialisation the v4l2_fh | |
986 | memory can be freed. | |
987 | ||
988 | ||
989 | If struct v4l2_fh is not embedded, then you can use these helper functions: | |
990 | ||
991 | int v4l2_fh_open(struct file *filp) | |
992 | ||
993 | This allocates a struct v4l2_fh, initializes it and adds it to the struct | |
994 | video_device associated with the file struct. | |
995 | ||
996 | int v4l2_fh_release(struct file *filp) | |
997 | ||
998 | This deletes it from the struct video_device associated with the file | |
999 | struct, uninitialised the v4l2_fh and frees it. | |
1000 | ||
1001 | These two functions can be plugged into the v4l2_file_operation's open() and | |
1002 | release() ops. | |
1003 | ||
1004 | ||
1005 | Several drivers need to do something when the first file handle is opened and | |
1006 | when the last file handle closes. Two helper functions were added to check | |
1007 | whether the v4l2_fh struct is the only open filehandle of the associated | |
1008 | device node: | |
1009 | ||
1010 | int v4l2_fh_is_singular(struct v4l2_fh *fh) | |
1011 | ||
1012 | Returns 1 if the file handle is the only open file handle, else 0. | |
1013 | ||
1014 | int v4l2_fh_is_singular_file(struct file *filp) | |
1015 | ||
1016 | Same, but it calls v4l2_fh_is_singular with filp->private_data. | |
1017 | ||
1018 | ||
dd966083 SA |
1019 | V4L2 events |
1020 | ----------- | |
1021 | ||
1022 | The V4L2 events provide a generic way to pass events to user space. | |
1023 | The driver must use v4l2_fh to be able to support V4L2 events. | |
1024 | ||
1de7310a HV |
1025 | Events are defined by a type and an optional ID. The ID may refer to a V4L2 |
1026 | object such as a control ID. If unused, then the ID is 0. | |
1027 | ||
1028 | When the user subscribes to an event the driver will allocate a number of | |
1029 | kevent structs for that event. So every (type, ID) event tuple will have | |
1030 | its own set of kevent structs. This guarantees that if a driver is generating | |
1031 | lots of events of one type in a short time, then that will not overwrite | |
1032 | events of another type. | |
1033 | ||
1034 | But if you get more events of one type than the number of kevents that were | |
1035 | reserved, then the oldest event will be dropped and the new one added. | |
1036 | ||
1037 | Furthermore, the internal struct v4l2_subscribed_event has merge() and | |
1038 | replace() callbacks which drivers can set. These callbacks are called when | |
1039 | a new event is raised and there is no more room. The replace() callback | |
1040 | allows you to replace the payload of the old event with that of the new event, | |
1041 | merging any relevant data from the old payload into the new payload that | |
1042 | replaces it. It is called when this event type has only one kevent struct | |
1043 | allocated. The merge() callback allows you to merge the oldest event payload | |
1044 | into that of the second-oldest event payload. It is called when there are two | |
1045 | or more kevent structs allocated. | |
dd966083 | 1046 | |
1de7310a HV |
1047 | This way no status information is lost, just the intermediate steps leading |
1048 | up to that state. | |
dd966083 | 1049 | |
1de7310a HV |
1050 | A good example of these replace/merge callbacks is in v4l2-event.c: |
1051 | ctrls_replace() and ctrls_merge() callbacks for the control event. | |
1052 | ||
1053 | Note: these callbacks can be called from interrupt context, so they must be | |
1054 | fast. | |
1055 | ||
1056 | Useful functions: | |
dd966083 | 1057 | |
c53c2549 | 1058 | void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev) |
dd966083 SA |
1059 | |
1060 | Queue events to video device. The driver's only responsibility is to fill | |
1061 | in the type and the data fields. The other fields will be filled in by | |
1062 | V4L2. | |
1063 | ||
c53c2549 HG |
1064 | int v4l2_event_subscribe(struct v4l2_fh *fh, |
1065 | struct v4l2_event_subscription *sub, unsigned elems, | |
1066 | const struct v4l2_subscribed_event_ops *ops) | |
dd966083 SA |
1067 | |
1068 | The video_device->ioctl_ops->vidioc_subscribe_event must check the driver | |
1069 | is able to produce events with specified event id. Then it calls | |
c53c2549 | 1070 | v4l2_event_subscribe() to subscribe the event. |
dd966083 | 1071 | |
c53c2549 HG |
1072 | The elems argument is the size of the event queue for this event. If it is 0, |
1073 | then the framework will fill in a default value (this depends on the event | |
1074 | type). | |
1075 | ||
1076 | The ops argument allows the driver to specify a number of callbacks: | |
1077 | * add: called when a new listener gets added (subscribing to the same | |
1078 | event twice will only cause this callback to get called once) | |
1079 | * del: called when a listener stops listening | |
1080 | * replace: replace event 'old' with event 'new'. | |
1081 | * merge: merge event 'old' into event 'new'. | |
1082 | All 4 callbacks are optional, if you don't want to specify any callbacks | |
1083 | the ops argument itself maybe NULL. | |
1084 | ||
1085 | int v4l2_event_unsubscribe(struct v4l2_fh *fh, | |
1086 | struct v4l2_event_subscription *sub) | |
dd966083 SA |
1087 | |
1088 | vidioc_unsubscribe_event in struct v4l2_ioctl_ops. A driver may use | |
1089 | v4l2_event_unsubscribe() directly unless it wants to be involved in | |
1090 | unsubscription process. | |
1091 | ||
1092 | The special type V4L2_EVENT_ALL may be used to unsubscribe all events. The | |
1093 | drivers may want to handle this in a special way. | |
1094 | ||
c53c2549 | 1095 | int v4l2_event_pending(struct v4l2_fh *fh) |
dd966083 SA |
1096 | |
1097 | Returns the number of pending events. Useful when implementing poll. | |
1098 | ||
dd966083 | 1099 | Events are delivered to user space through the poll system call. The driver |
1de7310a | 1100 | can use v4l2_fh->wait (a wait_queue_head_t) as the argument for poll_wait(). |
dd966083 SA |
1101 | |
1102 | There are standard and private events. New standard events must use the | |
1103 | smallest available event type. The drivers must allocate their events from | |
1104 | their own class starting from class base. Class base is | |
1105 | V4L2_EVENT_PRIVATE_START + n * 1000 where n is the lowest available number. | |
1106 | The first event type in the class is reserved for future use, so the first | |
1107 | available event type is 'class base + 1'. | |
1108 | ||
1109 | An example on how the V4L2 events may be used can be found in the OMAP | |
83c73537 | 1110 | 3 ISP driver (drivers/media/platform/omap3isp). |
c67f1a30 GL |
1111 | |
1112 | ||
1113 | V4L2 clocks | |
1114 | ----------- | |
1115 | ||
1116 | Many subdevices, like camera sensors, TV decoders and encoders, need a clock | |
1117 | signal to be supplied by the system. Often this clock is supplied by the | |
1118 | respective bridge device. The Linux kernel provides a Common Clock Framework for | |
1119 | this purpose. However, it is not (yet) available on all architectures. Besides, | |
1120 | the nature of the multi-functional (clock, data + synchronisation, I2C control) | |
1121 | connection of subdevices to the system might impose special requirements on the | |
1122 | clock API usage. E.g. V4L2 has to support clock provider driver unregistration | |
1123 | while a subdevice driver is holding a reference to the clock. For these reasons | |
1124 | a V4L2 clock helper API has been developed and is provided to bridge and | |
1125 | subdevice drivers. | |
1126 | ||
1127 | The API consists of two parts: two functions to register and unregister a V4L2 | |
1128 | clock source: v4l2_clk_register() and v4l2_clk_unregister() and calls to control | |
1129 | a clock object, similar to the respective generic clock API calls: | |
1130 | v4l2_clk_get(), v4l2_clk_put(), v4l2_clk_enable(), v4l2_clk_disable(), | |
1131 | v4l2_clk_get_rate(), and v4l2_clk_set_rate(). Clock suppliers have to provide | |
1132 | clock operations that will be called when clock users invoke respective API | |
1133 | methods. | |
1134 | ||
1135 | It is expected that once the CCF becomes available on all relevant | |
1136 | architectures this API will be removed. |