Root/
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 | |
47 | 3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX, /dev/radioX and |
48 | /dev/vtxX) and keeping track of device-node specific data. |
49 | |
50 | 4) Filehandle-specific structs containing per-filehandle data; |
51 | |
52 | 5) video buffer handling. |
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 |
71 | and in the future a v4l2_fh struct will keep track of filehandle instances |
72 | (this is not yet implemented). |
73 | |
74 | |
75 | struct v4l2_device |
76 | ------------------ |
77 | |
78 | Each device instance is represented by a struct v4l2_device (v4l2-device.h). |
79 | Very simple devices can just allocate this struct, but most of the time you |
80 | would embed this struct inside a larger struct. |
81 | |
82 | You must register the device instance: |
83 | |
84 | v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev); |
85 | |
86 | Registration will initialize the v4l2_device struct and link dev->driver_data |
87 | to v4l2_dev. If v4l2_dev->name is empty then it will be set to a value derived |
88 | from dev (driver name followed by the bus_id, to be precise). If you set it |
89 | up before calling v4l2_device_register then it will be untouched. If dev is |
90 | NULL, then you *must* setup v4l2_dev->name before calling v4l2_device_register. |
91 | |
92 | You can use v4l2_device_set_name() to set the name based on a driver name and |
93 | a driver-global atomic_t instance. This will generate names like ivtv0, ivtv1, |
94 | etc. If the name ends with a digit, then it will insert a dash: cx18-0, |
95 | cx18-1, etc. This function returns the instance number. |
96 | |
97 | The first 'dev' argument is normally the struct device pointer of a pci_dev, |
98 | usb_interface or platform_device. It is rare for dev to be NULL, but it happens |
99 | with ISA devices or when one device creates multiple PCI devices, thus making |
100 | it impossible to associate v4l2_dev with a particular parent. |
101 | |
102 | You can also supply a notify() callback that can be called by sub-devices to |
103 | notify you of events. Whether you need to set this depends on the sub-device. |
104 | Any notifications a sub-device supports must be defined in a header in |
105 | include/media/<subdevice>.h. |
106 | |
107 | You unregister with: |
108 | |
109 | v4l2_device_unregister(struct v4l2_device *v4l2_dev); |
110 | |
111 | Unregistering will also automatically unregister all subdevs from the device. |
112 | |
113 | If you have a hotpluggable device (e.g. a USB device), then when a disconnect |
114 | happens the parent device becomes invalid. Since v4l2_device has a pointer to |
115 | that parent device it has to be cleared as well to mark that the parent is |
116 | gone. To do this call: |
117 | |
118 | v4l2_device_disconnect(struct v4l2_device *v4l2_dev); |
119 | |
120 | This does *not* unregister the subdevs, so you still need to call the |
121 | v4l2_device_unregister() function for that. If your driver is not hotpluggable, |
122 | then there is no need to call v4l2_device_disconnect(). |
123 | |
124 | Sometimes you need to iterate over all devices registered by a specific |
125 | driver. This is usually the case if multiple device drivers use the same |
126 | hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv |
127 | hardware. The same is true for alsa drivers for example. |
128 | |
129 | You can iterate over all registered devices as follows: |
130 | |
131 | static int callback(struct device *dev, void *p) |
132 | { |
133 | struct v4l2_device *v4l2_dev = dev_get_drvdata(dev); |
134 | |
135 | /* test if this device was inited */ |
136 | if (v4l2_dev == NULL) |
137 | return 0; |
138 | ... |
139 | return 0; |
140 | } |
141 | |
142 | int iterate(void *p) |
143 | { |
144 | struct device_driver *drv; |
145 | int err; |
146 | |
147 | /* Find driver 'ivtv' on the PCI bus. |
148 | pci_bus_type is a global. For USB busses use usb_bus_type. */ |
149 | drv = driver_find("ivtv", &pci_bus_type); |
150 | /* iterate over all ivtv device instances */ |
151 | err = driver_for_each_device(drv, NULL, p, callback); |
152 | put_driver(drv); |
153 | return err; |
154 | } |
155 | |
156 | Sometimes you need to keep a running counter of the device instance. This is |
157 | commonly used to map a device instance to an index of a module option array. |
158 | |
159 | The recommended approach is as follows: |
160 | |
161 | static atomic_t drv_instance = ATOMIC_INIT(0); |
162 | |
163 | static int __devinit drv_probe(struct pci_dev *pdev, |
164 | const struct pci_device_id *pci_id) |
165 | { |
166 | ... |
167 | state->instance = atomic_inc_return(&drv_instance) - 1; |
168 | } |
169 | |
170 | |
171 | struct v4l2_subdev |
172 | ------------------ |
173 | |
174 | Many drivers need to communicate with sub-devices. These devices can do all |
175 | sort of tasks, but most commonly they handle audio and/or video muxing, |
176 | encoding or decoding. For webcams common sub-devices are sensors and camera |
177 | controllers. |
178 | |
179 | Usually these are I2C devices, but not necessarily. In order to provide the |
180 | driver with a consistent interface to these sub-devices the v4l2_subdev struct |
181 | (v4l2-subdev.h) was created. |
182 | |
183 | Each sub-device driver must have a v4l2_subdev struct. This struct can be |
184 | stand-alone for simple sub-devices or it might be embedded in a larger struct |
185 | if more state information needs to be stored. Usually there is a low-level |
186 | device struct (e.g. i2c_client) that contains the device data as setup |
187 | by the kernel. It is recommended to store that pointer in the private |
188 | data of v4l2_subdev using v4l2_set_subdevdata(). That makes it easy to go |
189 | from a v4l2_subdev to the actual low-level bus-specific device data. |
190 | |
191 | You also need a way to go from the low-level struct to v4l2_subdev. For the |
192 | common i2c_client struct the i2c_set_clientdata() call is used to store a |
193 | v4l2_subdev pointer, for other busses you may have to use other methods. |
194 | |
195 | From the bridge driver perspective you load the sub-device module and somehow |
196 | obtain the v4l2_subdev pointer. For i2c devices this is easy: you call |
197 | i2c_get_clientdata(). For other busses something similar needs to be done. |
198 | Helper functions exists for sub-devices on an I2C bus that do most of this |
199 | tricky work for you. |
200 | |
201 | Each v4l2_subdev contains function pointers that sub-device drivers can |
202 | implement (or leave NULL if it is not applicable). Since sub-devices can do |
203 | so many different things and you do not want to end up with a huge ops struct |
204 | of which only a handful of ops are commonly implemented, the function pointers |
205 | are sorted according to category and each category has its own ops struct. |
206 | |
207 | The top-level ops struct contains pointers to the category ops structs, which |
208 | may be NULL if the subdev driver does not support anything from that category. |
209 | |
210 | It looks like this: |
211 | |
212 | struct v4l2_subdev_core_ops { |
213 | int (*g_chip_ident)(struct v4l2_subdev *sd, struct v4l2_dbg_chip_ident *chip); |
214 | int (*log_status)(struct v4l2_subdev *sd); |
215 | int (*init)(struct v4l2_subdev *sd, u32 val); |
216 | ... |
217 | }; |
218 | |
219 | struct v4l2_subdev_tuner_ops { |
220 | ... |
221 | }; |
222 | |
223 | struct v4l2_subdev_audio_ops { |
224 | ... |
225 | }; |
226 | |
227 | struct v4l2_subdev_video_ops { |
228 | ... |
229 | }; |
230 | |
231 | struct v4l2_subdev_ops { |
232 | const struct v4l2_subdev_core_ops *core; |
233 | const struct v4l2_subdev_tuner_ops *tuner; |
234 | const struct v4l2_subdev_audio_ops *audio; |
235 | const struct v4l2_subdev_video_ops *video; |
236 | }; |
237 | |
238 | The core ops are common to all subdevs, the other categories are implemented |
239 | depending on the sub-device. E.g. a video device is unlikely to support the |
240 | audio ops and vice versa. |
241 | |
242 | This setup limits the number of function pointers while still making it easy |
243 | to add new ops and categories. |
244 | |
245 | A sub-device driver initializes the v4l2_subdev struct using: |
246 | |
247 | v4l2_subdev_init(sd, &ops); |
248 | |
249 | Afterwards you need to initialize subdev->name with a unique name and set the |
250 | module owner. This is done for you if you use the i2c helper functions. |
251 | |
252 | A device (bridge) driver needs to register the v4l2_subdev with the |
253 | v4l2_device: |
254 | |
255 | int err = v4l2_device_register_subdev(v4l2_dev, sd); |
256 | |
257 | This can fail if the subdev module disappeared before it could be registered. |
258 | After this function was called successfully the subdev->dev field points to |
259 | the v4l2_device. |
260 | |
261 | You can unregister a sub-device using: |
262 | |
263 | v4l2_device_unregister_subdev(sd); |
264 | |
265 | Afterwards the subdev module can be unloaded and sd->dev == NULL. |
266 | |
267 | You can call an ops function either directly: |
268 | |
269 | err = sd->ops->core->g_chip_ident(sd, &chip); |
270 | |
271 | but it is better and easier to use this macro: |
272 | |
273 | err = v4l2_subdev_call(sd, core, g_chip_ident, &chip); |
274 | |
275 | The macro will to the right NULL pointer checks and returns -ENODEV if subdev |
276 | is NULL, -ENOIOCTLCMD if either subdev->core or subdev->core->g_chip_ident is |
277 | NULL, or the actual result of the subdev->ops->core->g_chip_ident ops. |
278 | |
279 | It is also possible to call all or a subset of the sub-devices: |
280 | |
281 | v4l2_device_call_all(v4l2_dev, 0, core, g_chip_ident, &chip); |
282 | |
283 | Any subdev that does not support this ops is skipped and error results are |
284 | ignored. If you want to check for errors use this: |
285 | |
286 | err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_chip_ident, &chip); |
287 | |
288 | Any error except -ENOIOCTLCMD will exit the loop with that error. If no |
289 | errors (except -ENOIOCTLCMD) occured, then 0 is returned. |
290 | |
291 | The second argument to both calls is a group ID. If 0, then all subdevs are |
292 | called. If non-zero, then only those whose group ID match that value will |
293 | be called. Before a bridge driver registers a subdev it can set sd->grp_id |
294 | to whatever value it wants (it's 0 by default). This value is owned by the |
295 | bridge driver and the sub-device driver will never modify or use it. |
296 | |
297 | The group ID gives the bridge driver more control how callbacks are called. |
298 | For example, there may be multiple audio chips on a board, each capable of |
299 | changing the volume. But usually only one will actually be used when the |
300 | user want to change the volume. You can set the group ID for that subdev to |
301 | e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling |
302 | v4l2_device_call_all(). That ensures that it will only go to the subdev |
303 | that needs it. |
304 | |
305 | If the sub-device needs to notify its v4l2_device parent of an event, then |
306 | it can call v4l2_subdev_notify(sd, notification, arg). This macro checks |
307 | whether there is a notify() callback defined and returns -ENODEV if not. |
308 | Otherwise the result of the notify() call is returned. |
309 | |
310 | The advantage of using v4l2_subdev is that it is a generic struct and does |
311 | not contain any knowledge about the underlying hardware. So a driver might |
312 | contain several subdevs that use an I2C bus, but also a subdev that is |
313 | controlled through GPIO pins. This distinction is only relevant when setting |
314 | up the device, but once the subdev is registered it is completely transparent. |
315 | |
316 | |
317 | I2C sub-device drivers |
318 | ---------------------- |
319 | |
320 | Since these drivers are so common, special helper functions are available to |
321 | ease the use of these drivers (v4l2-common.h). |
322 | |
323 | The recommended method of adding v4l2_subdev support to an I2C driver is to |
324 | embed the v4l2_subdev struct into the state struct that is created for each |
325 | I2C device instance. Very simple devices have no state struct and in that case |
326 | you can just create a v4l2_subdev directly. |
327 | |
328 | A typical state struct would look like this (where 'chipname' is replaced by |
329 | the name of the chip): |
330 | |
331 | struct chipname_state { |
332 | struct v4l2_subdev sd; |
333 | ... /* additional state fields */ |
334 | }; |
335 | |
336 | Initialize the v4l2_subdev struct as follows: |
337 | |
338 | v4l2_i2c_subdev_init(&state->sd, client, subdev_ops); |
339 | |
340 | This function will fill in all the fields of v4l2_subdev and ensure that the |
341 | v4l2_subdev and i2c_client both point to one another. |
342 | |
343 | You should also add a helper inline function to go from a v4l2_subdev pointer |
344 | to a chipname_state struct: |
345 | |
346 | static inline struct chipname_state *to_state(struct v4l2_subdev *sd) |
347 | { |
348 | return container_of(sd, struct chipname_state, sd); |
349 | } |
350 | |
351 | Use this to go from the v4l2_subdev struct to the i2c_client struct: |
352 | |
353 | struct i2c_client *client = v4l2_get_subdevdata(sd); |
354 | |
355 | And this to go from an i2c_client to a v4l2_subdev struct: |
356 | |
357 | struct v4l2_subdev *sd = i2c_get_clientdata(client); |
358 | |
359 | Make sure to call v4l2_device_unregister_subdev(sd) when the remove() callback |
360 | is called. This will unregister the sub-device from the bridge driver. It is |
361 | safe to call this even if the sub-device was never registered. |
362 | |
363 | You need to do this because when the bridge driver destroys the i2c adapter |
364 | the remove() callbacks are called of the i2c devices on that adapter. |
365 | After that the corresponding v4l2_subdev structures are invalid, so they |
366 | have to be unregistered first. Calling v4l2_device_unregister_subdev(sd) |
367 | from the remove() callback ensures that this is always done correctly. |
368 | |
369 | |
370 | The bridge driver also has some helper functions it can use: |
371 | |
372 | struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter, |
373 | "module_foo", "chipid", 0x36, NULL); |
374 | |
375 | This loads the given module (can be NULL if no module needs to be loaded) and |
376 | calls i2c_new_device() with the given i2c_adapter and chip/address arguments. |
377 | If all goes well, then it registers the subdev with the v4l2_device. |
378 | |
379 | You can also use the last argument of v4l2_i2c_new_subdev() to pass an array |
380 | of possible I2C addresses that it should probe. These probe addresses are |
381 | only used if the previous argument is 0. A non-zero argument means that you |
382 | know the exact i2c address so in that case no probing will take place. |
383 | |
384 | Both functions return NULL if something went wrong. |
385 | |
386 | Note that the chipid you pass to v4l2_i2c_new_subdev() is usually |
387 | the same as the module name. It allows you to specify a chip variant, e.g. |
388 | "saa7114" or "saa7115". In general though the i2c driver autodetects this. |
389 | The use of chipid is something that needs to be looked at more closely at a |
390 | later date. It differs between i2c drivers and as such can be confusing. |
391 | To see which chip variants are supported you can look in the i2c driver code |
392 | for the i2c_device_id table. This lists all the possibilities. |
393 | |
394 | There are two more helper functions: |
395 | |
396 | v4l2_i2c_new_subdev_cfg: this function adds new irq and platform_data |
397 | arguments and has both 'addr' and 'probed_addrs' arguments: if addr is not |
398 | 0 then that will be used (non-probing variant), otherwise the probed_addrs |
399 | are probed. |
400 | |
401 | For example: this will probe for address 0x10: |
402 | |
403 | struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter, |
404 | "module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10)); |
405 | |
406 | v4l2_i2c_new_subdev_board uses an i2c_board_info struct which is passed |
407 | to the i2c driver and replaces the irq, platform_data and addr arguments. |
408 | |
409 | If the subdev supports the s_config core ops, then that op is called with |
410 | the irq and platform_data arguments after the subdev was setup. The older |
411 | v4l2_i2c_new_(probed_)subdev functions will call s_config as well, but with |
412 | irq set to 0 and platform_data set to NULL. |
413 | |
414 | struct video_device |
415 | ------------------- |
416 | |
417 | The actual device nodes in the /dev directory are created using the |
418 | video_device struct (v4l2-dev.h). This struct can either be allocated |
419 | dynamically or embedded in a larger struct. |
420 | |
421 | To allocate it dynamically use: |
422 | |
423 | struct video_device *vdev = video_device_alloc(); |
424 | |
425 | if (vdev == NULL) |
426 | return -ENOMEM; |
427 | |
428 | vdev->release = video_device_release; |
429 | |
430 | If you embed it in a larger struct, then you must set the release() |
431 | callback to your own function: |
432 | |
433 | struct video_device *vdev = &my_vdev->vdev; |
434 | |
435 | vdev->release = my_vdev_release; |
436 | |
437 | The release callback must be set and it is called when the last user |
438 | of the video device exits. |
439 | |
440 | The default video_device_release() callback just calls kfree to free the |
441 | allocated memory. |
442 | |
443 | You should also set these fields: |
444 | |
445 | - v4l2_dev: set to the v4l2_device parent device. |
446 | - name: set to something descriptive and unique. |
447 | - fops: set to the v4l2_file_operations struct. |
448 | - ioctl_ops: if you use the v4l2_ioctl_ops to simplify ioctl maintenance |
449 | (highly recommended to use this and it might become compulsory in the |
450 | future!), then set this to your v4l2_ioctl_ops struct. |
451 | - parent: you only set this if v4l2_device was registered with NULL as |
452 | the parent device struct. This only happens in cases where one hardware |
453 | device has multiple PCI devices that all share the same v4l2_device core. |
454 | |
455 | The cx88 driver is an example of this: one core v4l2_device struct, but |
456 | it is used by both an raw video PCI device (cx8800) and a MPEG PCI device |
457 | (cx8802). Since the v4l2_device cannot be associated with a particular |
458 | PCI device it is setup without a parent device. But when the struct |
459 | video_device is setup you do know which parent PCI device to use. |
460 | |
461 | If you use v4l2_ioctl_ops, then you should set either .unlocked_ioctl or |
462 | .ioctl to video_ioctl2 in your v4l2_file_operations struct. |
463 | |
464 | The v4l2_file_operations struct is a subset of file_operations. The main |
465 | difference is that the inode argument is omitted since it is never used. |
466 | |
467 | |
468 | video_device registration |
469 | ------------------------- |
470 | |
471 | Next you register the video device: this will create the character device |
472 | for you. |
473 | |
474 | err = video_register_device(vdev, VFL_TYPE_GRABBER, -1); |
475 | if (err) { |
476 | video_device_release(vdev); /* or kfree(my_vdev); */ |
477 | return err; |
478 | } |
479 | |
480 | Which device is registered depends on the type argument. The following |
481 | types exist: |
482 | |
483 | VFL_TYPE_GRABBER: videoX for video input/output devices |
484 | VFL_TYPE_VBI: vbiX for vertical blank data (i.e. closed captions, teletext) |
485 | VFL_TYPE_RADIO: radioX for radio tuners |
486 | VFL_TYPE_VTX: vtxX for teletext devices (deprecated, don't use) |
487 | |
488 | The last argument gives you a certain amount of control over the device |
489 | device node number used (i.e. the X in videoX). Normally you will pass -1 |
490 | to let the v4l2 framework pick the first free number. But sometimes users |
491 | want to select a specific node number. It is common that drivers allow |
492 | the user to select a specific device node number through a driver module |
493 | option. That number is then passed to this function and video_register_device |
494 | will attempt to select that device node number. If that number was already |
495 | in use, then the next free device node number will be selected and it |
496 | will send a warning to the kernel log. |
497 | |
498 | Another use-case is if a driver creates many devices. In that case it can |
499 | be useful to place different video devices in separate ranges. For example, |
500 | video capture devices start at 0, video output devices start at 16. |
501 | So you can use the last argument to specify a minimum device node number |
502 | and the v4l2 framework will try to pick the first free number that is equal |
503 | or higher to what you passed. If that fails, then it will just pick the |
504 | first free number. |
505 | |
506 | Since in this case you do not care about a warning about not being able |
507 | to select the specified device node number, you can call the function |
508 | video_register_device_no_warn() instead. |
509 | |
510 | Whenever a device node is created some attributes are also created for you. |
511 | If you look in /sys/class/video4linux you see the devices. Go into e.g. |
512 | video0 and you will see 'name' and 'index' attributes. The 'name' attribute |
513 | is the 'name' field of the video_device struct. |
514 | |
515 | The 'index' attribute is the index of the device node: for each call to |
516 | video_register_device() the index is just increased by 1. The first video |
517 | device node you register always starts with index 0. |
518 | |
519 | Users can setup udev rules that utilize the index attribute to make fancy |
520 | device names (e.g. 'mpegX' for MPEG video capture device nodes). |
521 | |
522 | After the device was successfully registered, then you can use these fields: |
523 | |
524 | - vfl_type: the device type passed to video_register_device. |
525 | - minor: the assigned device minor number. |
526 | - num: the device node number (i.e. the X in videoX). |
527 | - index: the device index number. |
528 | |
529 | If the registration failed, then you need to call video_device_release() |
530 | to free the allocated video_device struct, or free your own struct if the |
531 | video_device was embedded in it. The vdev->release() callback will never |
532 | be called if the registration failed, nor should you ever attempt to |
533 | unregister the device if the registration failed. |
534 | |
535 | |
536 | video_device cleanup |
537 | -------------------- |
538 | |
539 | When the video device nodes have to be removed, either during the unload |
540 | of the driver or because the USB device was disconnected, then you should |
541 | unregister them: |
542 | |
543 | video_unregister_device(vdev); |
544 | |
545 | This will remove the device nodes from sysfs (causing udev to remove them |
546 | from /dev). |
547 | |
548 | After video_unregister_device() returns no new opens can be done. |
549 | |
550 | However, in the case of USB devices some application might still have one |
551 | of these device nodes open. You should block all new accesses to read, |
552 | write, poll, etc. except possibly for certain ioctl operations like |
553 | queueing buffers. |
554 | |
555 | When the last user of the video device node exits, then the vdev->release() |
556 | callback is called and you can do the final cleanup there. |
557 | |
558 | |
559 | video_device helper functions |
560 | ----------------------------- |
561 | |
562 | There are a few useful helper functions: |
563 | |
564 | - file/video_device private data |
565 | |
566 | You can set/get driver private data in the video_device struct using: |
567 | |
568 | void *video_get_drvdata(struct video_device *vdev); |
569 | void video_set_drvdata(struct video_device *vdev, void *data); |
570 | |
571 | Note that you can safely call video_set_drvdata() before calling |
572 | video_register_device(). |
573 | |
574 | And this function: |
575 | |
576 | struct video_device *video_devdata(struct file *file); |
577 | |
578 | returns the video_device belonging to the file struct. |
579 | |
580 | The video_drvdata function combines video_get_drvdata with video_devdata: |
581 | |
582 | void *video_drvdata(struct file *file); |
583 | |
584 | You can go from a video_device struct to the v4l2_device struct using: |
585 | |
586 | struct v4l2_device *v4l2_dev = vdev->v4l2_dev; |
587 | |
588 | - Device node name |
589 | |
590 | The video_device node kernel name can be retrieved using |
591 | |
592 | const char *video_device_node_name(struct video_device *vdev); |
593 | |
594 | The name is used as a hint by userspace tools such as udev. The function |
595 | should be used where possible instead of accessing the video_device::num and |
596 | video_device::minor fields. |
597 | |
598 | |
599 | video buffer helper functions |
600 | ----------------------------- |
601 | |
602 | The v4l2 core API provides a set of standard methods (called "videobuf") |
603 | for dealing with video buffers. Those methods allow a driver to implement |
604 | read(), mmap() and overlay() in a consistent way. There are currently |
605 | methods for using video buffers on devices that supports DMA with |
606 | scatter/gather method (videobuf-dma-sg), DMA with linear access |
607 | (videobuf-dma-contig), and vmalloced buffers, mostly used on USB drivers |
608 | (videobuf-vmalloc). |
609 | |
610 | Please see Documentation/video4linux/videobuf for more information on how |
611 | to use the videobuf layer. |
612 |
Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master
Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9