1 Overview of the V4L2 driver framework
2 =====================================
4 This text documents the various structures provided by the V4L2 framework and
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
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
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).
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.
30 There is also a lot of common code that could never be refactored due to
31 the lack of a framework.
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.
41 All drivers have the following structure:
43 1) A struct for each device instance containing the device state.
45 2) A way of initializing and commanding sub-devices (if any).
47 3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX and /dev/radioX)
48 and keeping track of device-node specific data.
50 4) Filehandle-specific structs containing per-filehandle data;
52 5) video buffer handling.
54 This is a rough schematic of how it all relates:
58 +-sub-device instances
62 \-filehandle instances
65 Structure of the framework
66 --------------------------
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).
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.
82 You must register the device instance:
84 v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev);
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.
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.
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.
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.
109 v4l2_device_unregister(struct v4l2_device *v4l2_dev);
111 Unregistering will also automatically unregister all subdevs from the device.
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:
118 v4l2_device_disconnect(struct v4l2_device *v4l2_dev);
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().
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.
129 You can iterate over all registered devices as follows:
131 static int callback(struct device *dev, void *p)
133 struct v4l2_device *v4l2_dev = dev_get_drvdata(dev);
135 /* test if this device was inited */
136 if (v4l2_dev == NULL)
144 struct device_driver *drv;
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);
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.
159 The recommended approach is as follows:
161 static atomic_t drv_instance = ATOMIC_INIT(0);
163 static int __devinit drv_probe(struct pci_dev *pdev,
164 const struct pci_device_id *pci_id)
167 state->instance = atomic_inc_return(&drv_instance) - 1;
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
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.
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.
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.
195 Bridges might also need to store per-subdev private data, such as a pointer to
196 bridge-specific per-subdev private data. The v4l2_subdev structure provides
197 host private data for that purpose that can be accessed with
198 v4l2_get_subdev_hostdata() and v4l2_set_subdev_hostdata().
200 From the bridge driver perspective you load the sub-device module and somehow
201 obtain the v4l2_subdev pointer. For i2c devices this is easy: you call
202 i2c_get_clientdata(). For other busses something similar needs to be done.
203 Helper functions exists for sub-devices on an I2C bus that do most of this
206 Each v4l2_subdev contains function pointers that sub-device drivers can
207 implement (or leave NULL if it is not applicable). Since sub-devices can do
208 so many different things and you do not want to end up with a huge ops struct
209 of which only a handful of ops are commonly implemented, the function pointers
210 are sorted according to category and each category has its own ops struct.
212 The top-level ops struct contains pointers to the category ops structs, which
213 may be NULL if the subdev driver does not support anything from that category.
217 struct v4l2_subdev_core_ops {
218 int (*g_chip_ident)(struct v4l2_subdev *sd, struct v4l2_dbg_chip_ident *chip);
219 int (*log_status)(struct v4l2_subdev *sd);
220 int (*init)(struct v4l2_subdev *sd, u32 val);
224 struct v4l2_subdev_tuner_ops {
228 struct v4l2_subdev_audio_ops {
232 struct v4l2_subdev_video_ops {
236 struct v4l2_subdev_ops {
237 const struct v4l2_subdev_core_ops *core;
238 const struct v4l2_subdev_tuner_ops *tuner;
239 const struct v4l2_subdev_audio_ops *audio;
240 const struct v4l2_subdev_video_ops *video;
243 The core ops are common to all subdevs, the other categories are implemented
244 depending on the sub-device. E.g. a video device is unlikely to support the
245 audio ops and vice versa.
247 This setup limits the number of function pointers while still making it easy
248 to add new ops and categories.
250 A sub-device driver initializes the v4l2_subdev struct using:
252 v4l2_subdev_init(sd, &ops);
254 Afterwards you need to initialize subdev->name with a unique name and set the
255 module owner. This is done for you if you use the i2c helper functions.
257 A device (bridge) driver needs to register the v4l2_subdev with the
260 int err = v4l2_device_register_subdev(v4l2_dev, sd);
262 This can fail if the subdev module disappeared before it could be registered.
263 After this function was called successfully the subdev->dev field points to
266 You can unregister a sub-device using:
268 v4l2_device_unregister_subdev(sd);
270 Afterwards the subdev module can be unloaded and sd->dev == NULL.
272 You can call an ops function either directly:
274 err = sd->ops->core->g_chip_ident(sd, &chip);
276 but it is better and easier to use this macro:
278 err = v4l2_subdev_call(sd, core, g_chip_ident, &chip);
280 The macro will to the right NULL pointer checks and returns -ENODEV if subdev
281 is NULL, -ENOIOCTLCMD if either subdev->core or subdev->core->g_chip_ident is
282 NULL, or the actual result of the subdev->ops->core->g_chip_ident ops.
284 It is also possible to call all or a subset of the sub-devices:
286 v4l2_device_call_all(v4l2_dev, 0, core, g_chip_ident, &chip);
288 Any subdev that does not support this ops is skipped and error results are
289 ignored. If you want to check for errors use this:
291 err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_chip_ident, &chip);
293 Any error except -ENOIOCTLCMD will exit the loop with that error. If no
294 errors (except -ENOIOCTLCMD) occured, then 0 is returned.
296 The second argument to both calls is a group ID. If 0, then all subdevs are
297 called. If non-zero, then only those whose group ID match that value will
298 be called. Before a bridge driver registers a subdev it can set sd->grp_id
299 to whatever value it wants (it's 0 by default). This value is owned by the
300 bridge driver and the sub-device driver will never modify or use it.
302 The group ID gives the bridge driver more control how callbacks are called.
303 For example, there may be multiple audio chips on a board, each capable of
304 changing the volume. But usually only one will actually be used when the
305 user want to change the volume. You can set the group ID for that subdev to
306 e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling
307 v4l2_device_call_all(). That ensures that it will only go to the subdev
310 If the sub-device needs to notify its v4l2_device parent of an event, then
311 it can call v4l2_subdev_notify(sd, notification, arg). This macro checks
312 whether there is a notify() callback defined and returns -ENODEV if not.
313 Otherwise the result of the notify() call is returned.
315 The advantage of using v4l2_subdev is that it is a generic struct and does
316 not contain any knowledge about the underlying hardware. So a driver might
317 contain several subdevs that use an I2C bus, but also a subdev that is
318 controlled through GPIO pins. This distinction is only relevant when setting
319 up the device, but once the subdev is registered it is completely transparent.
322 V4L2 sub-device userspace API
323 -----------------------------
325 Beside exposing a kernel API through the v4l2_subdev_ops structure, V4L2
326 sub-devices can also be controlled directly by userspace applications.
328 Device nodes named v4l-subdevX can be created in /dev to access sub-devices
329 directly. If a sub-device supports direct userspace configuration it must set
330 the V4L2_SUBDEV_FL_HAS_DEVNODE flag before being registered.
332 After registering sub-devices, the v4l2_device driver can create device nodes
333 for all registered sub-devices marked with V4L2_SUBDEV_FL_HAS_DEVNODE by calling
334 v4l2_device_register_subdev_nodes(). Those device nodes will be automatically
335 removed when sub-devices are unregistered.
337 The device node handles a subset of the V4L2 API.
347 The controls ioctls are identical to the ones defined in V4L2. They
348 behave identically, with the only exception that they deal only with
349 controls implemented in the sub-device. Depending on the driver, those
350 controls can be also be accessed through one (or several) V4L2 device
354 VIDIOC_SUBSCRIBE_EVENT
355 VIDIOC_UNSUBSCRIBE_EVENT
357 The events ioctls are identical to the ones defined in V4L2. They
358 behave identically, with the only exception that they deal only with
359 events generated by the sub-device. Depending on the driver, those
360 events can also be reported by one (or several) V4L2 device nodes.
362 Sub-device drivers that want to use events need to set the
363 V4L2_SUBDEV_USES_EVENTS v4l2_subdev::flags and initialize
364 v4l2_subdev::nevents to events queue depth before registering the
365 sub-device. After registration events can be queued as usual on the
366 v4l2_subdev::devnode device node.
368 To properly support events, the poll() file operation is also
372 I2C sub-device drivers
373 ----------------------
375 Since these drivers are so common, special helper functions are available to
376 ease the use of these drivers (v4l2-common.h).
378 The recommended method of adding v4l2_subdev support to an I2C driver is to
379 embed the v4l2_subdev struct into the state struct that is created for each
380 I2C device instance. Very simple devices have no state struct and in that case
381 you can just create a v4l2_subdev directly.
383 A typical state struct would look like this (where 'chipname' is replaced by
384 the name of the chip):
386 struct chipname_state {
387 struct v4l2_subdev sd;
388 ... /* additional state fields */
391 Initialize the v4l2_subdev struct as follows:
393 v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
395 This function will fill in all the fields of v4l2_subdev and ensure that the
396 v4l2_subdev and i2c_client both point to one another.
398 You should also add a helper inline function to go from a v4l2_subdev pointer
399 to a chipname_state struct:
401 static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
403 return container_of(sd, struct chipname_state, sd);
406 Use this to go from the v4l2_subdev struct to the i2c_client struct:
408 struct i2c_client *client = v4l2_get_subdevdata(sd);
410 And this to go from an i2c_client to a v4l2_subdev struct:
412 struct v4l2_subdev *sd = i2c_get_clientdata(client);
414 Make sure to call v4l2_device_unregister_subdev(sd) when the remove() callback
415 is called. This will unregister the sub-device from the bridge driver. It is
416 safe to call this even if the sub-device was never registered.
418 You need to do this because when the bridge driver destroys the i2c adapter
419 the remove() callbacks are called of the i2c devices on that adapter.
420 After that the corresponding v4l2_subdev structures are invalid, so they
421 have to be unregistered first. Calling v4l2_device_unregister_subdev(sd)
422 from the remove() callback ensures that this is always done correctly.
425 The bridge driver also has some helper functions it can use:
427 struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
428 "module_foo", "chipid", 0x36, NULL);
430 This loads the given module (can be NULL if no module needs to be loaded) and
431 calls i2c_new_device() with the given i2c_adapter and chip/address arguments.
432 If all goes well, then it registers the subdev with the v4l2_device.
434 You can also use the last argument of v4l2_i2c_new_subdev() to pass an array
435 of possible I2C addresses that it should probe. These probe addresses are
436 only used if the previous argument is 0. A non-zero argument means that you
437 know the exact i2c address so in that case no probing will take place.
439 Both functions return NULL if something went wrong.
441 Note that the chipid you pass to v4l2_i2c_new_subdev() is usually
442 the same as the module name. It allows you to specify a chip variant, e.g.
443 "saa7114" or "saa7115". In general though the i2c driver autodetects this.
444 The use of chipid is something that needs to be looked at more closely at a
445 later date. It differs between i2c drivers and as such can be confusing.
446 To see which chip variants are supported you can look in the i2c driver code
447 for the i2c_device_id table. This lists all the possibilities.
449 There are two more helper functions:
451 v4l2_i2c_new_subdev_cfg: this function adds new irq and platform_data
452 arguments and has both 'addr' and 'probed_addrs' arguments: if addr is not
453 0 then that will be used (non-probing variant), otherwise the probed_addrs
456 For example: this will probe for address 0x10:
458 struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter,
459 "module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10));
461 v4l2_i2c_new_subdev_board uses an i2c_board_info struct which is passed
462 to the i2c driver and replaces the irq, platform_data and addr arguments.
464 If the subdev supports the s_config core ops, then that op is called with
465 the irq and platform_data arguments after the subdev was setup. The older
466 v4l2_i2c_new_(probed_)subdev functions will call s_config as well, but with
467 irq set to 0 and platform_data set to NULL.
472 The actual device nodes in the /dev directory are created using the
473 video_device struct (v4l2-dev.h). This struct can either be allocated
474 dynamically or embedded in a larger struct.
476 To allocate it dynamically use:
478 struct video_device *vdev = video_device_alloc();
483 vdev->release = video_device_release;
485 If you embed it in a larger struct, then you must set the release()
486 callback to your own function:
488 struct video_device *vdev = &my_vdev->vdev;
490 vdev->release = my_vdev_release;
492 The release callback must be set and it is called when the last user
493 of the video device exits.
495 The default video_device_release() callback just calls kfree to free the
498 You should also set these fields:
500 - v4l2_dev: set to the v4l2_device parent device.
501 - name: set to something descriptive and unique.
502 - fops: set to the v4l2_file_operations struct.
503 - ioctl_ops: if you use the v4l2_ioctl_ops to simplify ioctl maintenance
504 (highly recommended to use this and it might become compulsory in the
505 future!), then set this to your v4l2_ioctl_ops struct.
506 - lock: leave to NULL if you want to do all the locking in the driver.
507 Otherwise you give it a pointer to a struct mutex_lock and before any
508 of the v4l2_file_operations is called this lock will be taken by the
509 core and released afterwards.
510 - parent: you only set this if v4l2_device was registered with NULL as
511 the parent device struct. This only happens in cases where one hardware
512 device has multiple PCI devices that all share the same v4l2_device core.
514 The cx88 driver is an example of this: one core v4l2_device struct, but
515 it is used by both an raw video PCI device (cx8800) and a MPEG PCI device
516 (cx8802). Since the v4l2_device cannot be associated with a particular
517 PCI device it is setup without a parent device. But when the struct
518 video_device is setup you do know which parent PCI device to use.
520 If you use v4l2_ioctl_ops, then you should set either .unlocked_ioctl or
521 .ioctl to video_ioctl2 in your v4l2_file_operations struct.
523 The v4l2_file_operations struct is a subset of file_operations. The main
524 difference is that the inode argument is omitted since it is never used.
526 v4l2_file_operations and locking
527 --------------------------------
529 You can set a pointer to a mutex_lock in struct video_device. Usually this
530 will be either a top-level mutex or a mutex per device node. If you want
531 finer-grained locking then you have to set it to NULL and do you own locking.
533 If a lock is specified then all file operations will be serialized on that
534 lock. If you use videobuf then you must pass the same lock to the videobuf
535 queue initialize function: if videobuf has to wait for a frame to arrive, then
536 it will temporarily unlock the lock and relock it afterwards. If your driver
537 also waits in the code, then you should do the same to allow other processes
538 to access the device node while the first process is waiting for something.
540 The implementation of a hotplug disconnect should also take the lock before
541 calling v4l2_device_disconnect.
543 video_device registration
544 -------------------------
546 Next you register the video device: this will create the character device
549 err = video_register_device(vdev, VFL_TYPE_GRABBER, -1);
551 video_device_release(vdev); /* or kfree(my_vdev); */
555 Which device is registered depends on the type argument. The following
558 VFL_TYPE_GRABBER: videoX for video input/output devices
559 VFL_TYPE_VBI: vbiX for vertical blank data (i.e. closed captions, teletext)
560 VFL_TYPE_RADIO: radioX for radio tuners
562 The last argument gives you a certain amount of control over the device
563 device node number used (i.e. the X in videoX). Normally you will pass -1
564 to let the v4l2 framework pick the first free number. But sometimes users
565 want to select a specific node number. It is common that drivers allow
566 the user to select a specific device node number through a driver module
567 option. That number is then passed to this function and video_register_device
568 will attempt to select that device node number. If that number was already
569 in use, then the next free device node number will be selected and it
570 will send a warning to the kernel log.
572 Another use-case is if a driver creates many devices. In that case it can
573 be useful to place different video devices in separate ranges. For example,
574 video capture devices start at 0, video output devices start at 16.
575 So you can use the last argument to specify a minimum device node number
576 and the v4l2 framework will try to pick the first free number that is equal
577 or higher to what you passed. If that fails, then it will just pick the
580 Since in this case you do not care about a warning about not being able
581 to select the specified device node number, you can call the function
582 video_register_device_no_warn() instead.
584 Whenever a device node is created some attributes are also created for you.
585 If you look in /sys/class/video4linux you see the devices. Go into e.g.
586 video0 and you will see 'name' and 'index' attributes. The 'name' attribute
587 is the 'name' field of the video_device struct.
589 The 'index' attribute is the index of the device node: for each call to
590 video_register_device() the index is just increased by 1. The first video
591 device node you register always starts with index 0.
593 Users can setup udev rules that utilize the index attribute to make fancy
594 device names (e.g. 'mpegX' for MPEG video capture device nodes).
596 After the device was successfully registered, then you can use these fields:
598 - vfl_type: the device type passed to video_register_device.
599 - minor: the assigned device minor number.
600 - num: the device node number (i.e. the X in videoX).
601 - index: the device index number.
603 If the registration failed, then you need to call video_device_release()
604 to free the allocated video_device struct, or free your own struct if the
605 video_device was embedded in it. The vdev->release() callback will never
606 be called if the registration failed, nor should you ever attempt to
607 unregister the device if the registration failed.
613 When the video device nodes have to be removed, either during the unload
614 of the driver or because the USB device was disconnected, then you should
617 video_unregister_device(vdev);
619 This will remove the device nodes from sysfs (causing udev to remove them
622 After video_unregister_device() returns no new opens can be done. However,
623 in the case of USB devices some application might still have one of these
624 device nodes open. So after the unregister all file operations (except
625 release, of course) will return an error as well.
627 When the last user of the video device node exits, then the vdev->release()
628 callback is called and you can do the final cleanup there.
631 video_device helper functions
632 -----------------------------
634 There are a few useful helper functions:
636 - file/video_device private data
638 You can set/get driver private data in the video_device struct using:
640 void *video_get_drvdata(struct video_device *vdev);
641 void video_set_drvdata(struct video_device *vdev, void *data);
643 Note that you can safely call video_set_drvdata() before calling
644 video_register_device().
648 struct video_device *video_devdata(struct file *file);
650 returns the video_device belonging to the file struct.
652 The video_drvdata function combines video_get_drvdata with video_devdata:
654 void *video_drvdata(struct file *file);
656 You can go from a video_device struct to the v4l2_device struct using:
658 struct v4l2_device *v4l2_dev = vdev->v4l2_dev;
662 The video_device node kernel name can be retrieved using
664 const char *video_device_node_name(struct video_device *vdev);
666 The name is used as a hint by userspace tools such as udev. The function
667 should be used where possible instead of accessing the video_device::num and
668 video_device::minor fields.
671 video buffer helper functions
672 -----------------------------
674 The v4l2 core API provides a set of standard methods (called "videobuf")
675 for dealing with video buffers. Those methods allow a driver to implement
676 read(), mmap() and overlay() in a consistent way. There are currently
677 methods for using video buffers on devices that supports DMA with
678 scatter/gather method (videobuf-dma-sg), DMA with linear access
679 (videobuf-dma-contig), and vmalloced buffers, mostly used on USB drivers
682 Please see Documentation/video4linux/videobuf for more information on how
683 to use the videobuf layer.
688 struct v4l2_fh provides a way to easily keep file handle specific data
689 that is used by the V4L2 framework. Using v4l2_fh is optional for
692 The users of v4l2_fh (in the V4L2 framework, not the driver) know
693 whether a driver uses v4l2_fh as its file->private_data pointer by
694 testing the V4L2_FL_USES_V4L2_FH bit in video_device->flags.
700 Initialise the file handle. This *MUST* be performed in the driver's
701 v4l2_file_operations->open() handler.
705 Add a v4l2_fh to video_device file handle list. May be called after
706 initialising the file handle.
710 Unassociate the file handle from video_device(). The file handle
711 exit function may now be called.
715 Uninitialise the file handle. After uninitialisation the v4l2_fh
718 struct v4l2_fh is allocated as a part of the driver's own file handle
719 structure and is set to file->private_data in the driver's open
720 function by the driver. Drivers can extract their own file handle
721 structure by using the container_of macro. Example:
730 int my_open(struct file *file)
733 struct video_device *vfd;
738 ret = v4l2_fh_init(&my_fh->fh, vfd);
742 v4l2_fh_add(&my_fh->fh);
744 file->private_data = &my_fh->fh;
749 int my_release(struct file *file)
751 struct v4l2_fh *fh = file->private_data;
752 struct my_fh *my_fh = container_of(fh, struct my_fh, fh);
760 The V4L2 events provide a generic way to pass events to user space.
761 The driver must use v4l2_fh to be able to support V4L2 events.
767 To use events, the driver must allocate events for the file handle. By
768 calling the function more than once, the driver may assure that at least n
769 events in total have been allocated. The function may not be called in
774 Queue events to video device. The driver's only responsibility is to fill
775 in the type and the data fields. The other fields will be filled in by
778 - v4l2_event_subscribe()
780 The video_device->ioctl_ops->vidioc_subscribe_event must check the driver
781 is able to produce events with specified event id. Then it calls
782 v4l2_event_subscribe() to subscribe the event.
784 - v4l2_event_unsubscribe()
786 vidioc_unsubscribe_event in struct v4l2_ioctl_ops. A driver may use
787 v4l2_event_unsubscribe() directly unless it wants to be involved in
788 unsubscription process.
790 The special type V4L2_EVENT_ALL may be used to unsubscribe all events. The
791 drivers may want to handle this in a special way.
793 - v4l2_event_pending()
795 Returns the number of pending events. Useful when implementing poll.
797 Drivers do not initialise events directly. The events are initialised
798 through v4l2_fh_init() if video_device->ioctl_ops->vidioc_subscribe_event is
799 non-NULL. This *MUST* be performed in the driver's
800 v4l2_file_operations->open() handler.
802 Events are delivered to user space through the poll system call. The driver
803 can use v4l2_fh->events->wait wait_queue_head_t as the argument for
806 There are standard and private events. New standard events must use the
807 smallest available event type. The drivers must allocate their events from
808 their own class starting from class base. Class base is
809 V4L2_EVENT_PRIVATE_START + n * 1000 where n is the lowest available number.
810 The first event type in the class is reserved for future use, so the first
811 available event type is 'class base + 1'.
813 An example on how the V4L2 events may be used can be found in the OMAP
814 3 ISP driver available at <URL:http://gitorious.org/omap3camera> as of