Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 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 | |
Hans Verkuil | f44026d | 2010-08-06 12:52:43 -0300 | [diff] [blame] | 47 | 3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX and /dev/radioX) |
| 48 | and keeping track of device-node specific data. |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 49 | |
Mauro Carvalho Chehab | 44061c0 | 2009-02-14 07:29:07 -0300 | [diff] [blame] | 50 | 4) Filehandle-specific structs containing per-filehandle data; |
| 51 | |
| 52 | 5) video buffer handling. |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 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 | |
Laurent Pinchart | 2c0ab67 | 2009-12-09 08:40:10 -0300 | [diff] [blame] | 74 | The V4L2 framework also optionally integrates with the media framework. If a |
| 75 | driver sets the struct v4l2_device mdev field, sub-devices and video nodes |
| 76 | will automatically appear in the media framework as entities. |
| 77 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 78 | |
| 79 | struct v4l2_device |
| 80 | ------------------ |
| 81 | |
| 82 | Each device instance is represented by a struct v4l2_device (v4l2-device.h). |
| 83 | Very simple devices can just allocate this struct, but most of the time you |
| 84 | would embed this struct inside a larger struct. |
| 85 | |
| 86 | You must register the device instance: |
| 87 | |
| 88 | v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev); |
| 89 | |
Laurent Pinchart | 95db3a6 | 2009-12-09 08:40:05 -0300 | [diff] [blame] | 90 | Registration will initialize the v4l2_device struct. If the dev->driver_data |
Laurent Pinchart | 2c0ab67 | 2009-12-09 08:40:10 -0300 | [diff] [blame] | 91 | field is NULL, it will be linked to v4l2_dev. |
| 92 | |
| 93 | Drivers that want integration with the media device framework need to set |
Laurent Pinchart | 95db3a6 | 2009-12-09 08:40:05 -0300 | [diff] [blame] | 94 | dev->driver_data manually to point to the driver-specific device structure |
| 95 | that embed the struct v4l2_device instance. This is achieved by a |
Laurent Pinchart | 2c0ab67 | 2009-12-09 08:40:10 -0300 | [diff] [blame] | 96 | dev_set_drvdata() call before registering the V4L2 device instance. They must |
| 97 | also set the struct v4l2_device mdev field to point to a properly initialized |
| 98 | and registered media_device instance. |
Laurent Pinchart | 95db3a6 | 2009-12-09 08:40:05 -0300 | [diff] [blame] | 99 | |
| 100 | If v4l2_dev->name is empty then it will be set to a value derived from dev |
| 101 | (driver name followed by the bus_id, to be precise). If you set it up before |
| 102 | calling v4l2_device_register then it will be untouched. If dev is NULL, then |
| 103 | you *must* setup v4l2_dev->name before calling v4l2_device_register. |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 104 | |
Hans Verkuil | 102e781 | 2009-05-02 10:12:50 -0300 | [diff] [blame] | 105 | You can use v4l2_device_set_name() to set the name based on a driver name and |
| 106 | a driver-global atomic_t instance. This will generate names like ivtv0, ivtv1, |
| 107 | etc. If the name ends with a digit, then it will insert a dash: cx18-0, |
| 108 | cx18-1, etc. This function returns the instance number. |
| 109 | |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 110 | The first 'dev' argument is normally the struct device pointer of a pci_dev, |
Janne Grunau | 073d696 | 2009-04-01 08:30:06 -0300 | [diff] [blame] | 111 | usb_interface or platform_device. It is rare for dev to be NULL, but it happens |
Hans Verkuil | 0057596 | 2009-03-13 10:03:04 -0300 | [diff] [blame] | 112 | with ISA devices or when one device creates multiple PCI devices, thus making |
| 113 | it impossible to associate v4l2_dev with a particular parent. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 114 | |
Hans Verkuil | 98ec633 | 2009-03-08 17:02:10 -0300 | [diff] [blame] | 115 | You can also supply a notify() callback that can be called by sub-devices to |
| 116 | notify you of events. Whether you need to set this depends on the sub-device. |
| 117 | Any notifications a sub-device supports must be defined in a header in |
| 118 | include/media/<subdevice>.h. |
| 119 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 120 | You unregister with: |
| 121 | |
| 122 | v4l2_device_unregister(struct v4l2_device *v4l2_dev); |
| 123 | |
Laurent Pinchart | 95db3a6 | 2009-12-09 08:40:05 -0300 | [diff] [blame] | 124 | If the dev->driver_data field points to v4l2_dev, it will be reset to NULL. |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 125 | Unregistering will also automatically unregister all subdevs from the device. |
| 126 | |
Hans Verkuil | ae6cfaa | 2009-03-14 08:28:45 -0300 | [diff] [blame] | 127 | If you have a hotpluggable device (e.g. a USB device), then when a disconnect |
| 128 | happens the parent device becomes invalid. Since v4l2_device has a pointer to |
| 129 | that parent device it has to be cleared as well to mark that the parent is |
| 130 | gone. To do this call: |
| 131 | |
| 132 | v4l2_device_disconnect(struct v4l2_device *v4l2_dev); |
| 133 | |
| 134 | This does *not* unregister the subdevs, so you still need to call the |
| 135 | v4l2_device_unregister() function for that. If your driver is not hotpluggable, |
| 136 | then there is no need to call v4l2_device_disconnect(). |
| 137 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 138 | Sometimes you need to iterate over all devices registered by a specific |
| 139 | driver. This is usually the case if multiple device drivers use the same |
| 140 | hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv |
| 141 | hardware. The same is true for alsa drivers for example. |
| 142 | |
| 143 | You can iterate over all registered devices as follows: |
| 144 | |
| 145 | static int callback(struct device *dev, void *p) |
| 146 | { |
| 147 | struct v4l2_device *v4l2_dev = dev_get_drvdata(dev); |
| 148 | |
| 149 | /* test if this device was inited */ |
| 150 | if (v4l2_dev == NULL) |
| 151 | return 0; |
| 152 | ... |
| 153 | return 0; |
| 154 | } |
| 155 | |
| 156 | int iterate(void *p) |
| 157 | { |
| 158 | struct device_driver *drv; |
| 159 | int err; |
| 160 | |
| 161 | /* Find driver 'ivtv' on the PCI bus. |
| 162 | pci_bus_type is a global. For USB busses use usb_bus_type. */ |
| 163 | drv = driver_find("ivtv", &pci_bus_type); |
| 164 | /* iterate over all ivtv device instances */ |
| 165 | err = driver_for_each_device(drv, NULL, p, callback); |
| 166 | put_driver(drv); |
| 167 | return err; |
| 168 | } |
| 169 | |
| 170 | Sometimes you need to keep a running counter of the device instance. This is |
| 171 | commonly used to map a device instance to an index of a module option array. |
| 172 | |
| 173 | The recommended approach is as follows: |
| 174 | |
| 175 | static atomic_t drv_instance = ATOMIC_INIT(0); |
| 176 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 177 | static int __devinit drv_probe(struct pci_dev *pdev, |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 178 | const struct pci_device_id *pci_id) |
| 179 | { |
| 180 | ... |
| 181 | state->instance = atomic_inc_return(&drv_instance) - 1; |
| 182 | } |
| 183 | |
Hans Verkuil | 2335e2b | 2011-02-24 06:28:46 -0300 | [diff] [blame] | 184 | If you have multiple device nodes then it can be difficult to know when it is |
Hans Verkuil | ee71e7b | 2012-04-19 12:27:56 -0300 | [diff] [blame] | 185 | safe to unregister v4l2_device for hotpluggable devices. For this purpose |
| 186 | v4l2_device has refcounting support. The refcount is increased whenever |
| 187 | video_register_device is called and it is decreased whenever that device node |
| 188 | is released. When the refcount reaches zero, then the v4l2_device release() |
| 189 | callback is called. You can do your final cleanup there. |
Hans Verkuil | 2335e2b | 2011-02-24 06:28:46 -0300 | [diff] [blame] | 190 | |
| 191 | If other device nodes (e.g. ALSA) are created, then you can increase and |
| 192 | decrease the refcount manually as well by calling: |
| 193 | |
| 194 | void v4l2_device_get(struct v4l2_device *v4l2_dev); |
| 195 | |
| 196 | or: |
| 197 | |
| 198 | int v4l2_device_put(struct v4l2_device *v4l2_dev); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 199 | |
Hans Verkuil | ee71e7b | 2012-04-19 12:27:56 -0300 | [diff] [blame] | 200 | Since the initial refcount is 1 you also need to call v4l2_device_put in the |
| 201 | disconnect() callback (for USB devices) or in the remove() callback (for e.g. |
| 202 | PCI devices), otherwise the refcount will never reach 0. |
| 203 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 204 | struct v4l2_subdev |
| 205 | ------------------ |
| 206 | |
| 207 | Many drivers need to communicate with sub-devices. These devices can do all |
| 208 | sort of tasks, but most commonly they handle audio and/or video muxing, |
| 209 | encoding or decoding. For webcams common sub-devices are sensors and camera |
| 210 | controllers. |
| 211 | |
| 212 | Usually these are I2C devices, but not necessarily. In order to provide the |
| 213 | driver with a consistent interface to these sub-devices the v4l2_subdev struct |
| 214 | (v4l2-subdev.h) was created. |
| 215 | |
| 216 | Each sub-device driver must have a v4l2_subdev struct. This struct can be |
| 217 | stand-alone for simple sub-devices or it might be embedded in a larger struct |
| 218 | if more state information needs to be stored. Usually there is a low-level |
| 219 | device struct (e.g. i2c_client) that contains the device data as setup |
| 220 | by the kernel. It is recommended to store that pointer in the private |
| 221 | data of v4l2_subdev using v4l2_set_subdevdata(). That makes it easy to go |
| 222 | from a v4l2_subdev to the actual low-level bus-specific device data. |
| 223 | |
| 224 | You also need a way to go from the low-level struct to v4l2_subdev. For the |
| 225 | common i2c_client struct the i2c_set_clientdata() call is used to store a |
| 226 | v4l2_subdev pointer, for other busses you may have to use other methods. |
| 227 | |
Laurent Pinchart | 692d5522 | 2010-07-30 17:24:55 -0300 | [diff] [blame] | 228 | Bridges might also need to store per-subdev private data, such as a pointer to |
| 229 | bridge-specific per-subdev private data. The v4l2_subdev structure provides |
| 230 | host private data for that purpose that can be accessed with |
| 231 | v4l2_get_subdev_hostdata() and v4l2_set_subdev_hostdata(). |
| 232 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 233 | From the bridge driver perspective you load the sub-device module and somehow |
| 234 | obtain the v4l2_subdev pointer. For i2c devices this is easy: you call |
| 235 | i2c_get_clientdata(). For other busses something similar needs to be done. |
| 236 | Helper functions exists for sub-devices on an I2C bus that do most of this |
| 237 | tricky work for you. |
| 238 | |
| 239 | Each v4l2_subdev contains function pointers that sub-device drivers can |
| 240 | implement (or leave NULL if it is not applicable). Since sub-devices can do |
| 241 | so many different things and you do not want to end up with a huge ops struct |
| 242 | of which only a handful of ops are commonly implemented, the function pointers |
| 243 | are sorted according to category and each category has its own ops struct. |
| 244 | |
| 245 | The top-level ops struct contains pointers to the category ops structs, which |
| 246 | may be NULL if the subdev driver does not support anything from that category. |
| 247 | |
| 248 | It looks like this: |
| 249 | |
| 250 | struct v4l2_subdev_core_ops { |
Hans Verkuil | aecde8b5 | 2008-12-30 07:14:19 -0300 | [diff] [blame] | 251 | int (*g_chip_ident)(struct v4l2_subdev *sd, struct v4l2_dbg_chip_ident *chip); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 252 | int (*log_status)(struct v4l2_subdev *sd); |
| 253 | int (*init)(struct v4l2_subdev *sd, u32 val); |
| 254 | ... |
| 255 | }; |
| 256 | |
| 257 | struct v4l2_subdev_tuner_ops { |
| 258 | ... |
| 259 | }; |
| 260 | |
| 261 | struct v4l2_subdev_audio_ops { |
| 262 | ... |
| 263 | }; |
| 264 | |
| 265 | struct v4l2_subdev_video_ops { |
| 266 | ... |
| 267 | }; |
| 268 | |
Sakari Ailus | 48398f9 | 2012-01-23 03:03:00 -0300 | [diff] [blame] | 269 | struct v4l2_subdev_pad_ops { |
| 270 | ... |
| 271 | }; |
| 272 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 273 | struct v4l2_subdev_ops { |
| 274 | const struct v4l2_subdev_core_ops *core; |
| 275 | const struct v4l2_subdev_tuner_ops *tuner; |
| 276 | const struct v4l2_subdev_audio_ops *audio; |
| 277 | const struct v4l2_subdev_video_ops *video; |
Sakari Ailus | 48398f9 | 2012-01-23 03:03:00 -0300 | [diff] [blame] | 278 | const struct v4l2_subdev_pad_ops *video; |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 279 | }; |
| 280 | |
| 281 | The core ops are common to all subdevs, the other categories are implemented |
| 282 | depending on the sub-device. E.g. a video device is unlikely to support the |
| 283 | audio ops and vice versa. |
| 284 | |
| 285 | This setup limits the number of function pointers while still making it easy |
| 286 | to add new ops and categories. |
| 287 | |
| 288 | A sub-device driver initializes the v4l2_subdev struct using: |
| 289 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 290 | v4l2_subdev_init(sd, &ops); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 291 | |
| 292 | Afterwards you need to initialize subdev->name with a unique name and set the |
| 293 | module owner. This is done for you if you use the i2c helper functions. |
| 294 | |
Laurent Pinchart | 61f5db5 | 2009-12-09 08:40:08 -0300 | [diff] [blame] | 295 | If integration with the media framework is needed, you must initialize the |
| 296 | media_entity struct embedded in the v4l2_subdev struct (entity field) by |
| 297 | calling media_entity_init(): |
| 298 | |
| 299 | struct media_pad *pads = &my_sd->pads; |
| 300 | int err; |
| 301 | |
| 302 | err = media_entity_init(&sd->entity, npads, pads, 0); |
| 303 | |
| 304 | The pads array must have been previously initialized. There is no need to |
| 305 | manually set the struct media_entity type and name fields, but the revision |
| 306 | field must be initialized if needed. |
| 307 | |
| 308 | A reference to the entity will be automatically acquired/released when the |
| 309 | subdev device node (if any) is opened/closed. |
| 310 | |
| 311 | Don't forget to cleanup the media entity before the sub-device is destroyed: |
| 312 | |
| 313 | media_entity_cleanup(&sd->entity); |
| 314 | |
Sakari Ailus | 48398f9 | 2012-01-23 03:03:00 -0300 | [diff] [blame] | 315 | If the subdev driver intends to process video and integrate with the media |
| 316 | framework, it must implement format related functionality using |
| 317 | v4l2_subdev_pad_ops instead of v4l2_subdev_video_ops. |
| 318 | |
Sakari Ailus | 8227c92 | 2011-10-10 17:01:25 -0300 | [diff] [blame] | 319 | In that case, the subdev driver may set the link_validate field to provide |
| 320 | its own link validation function. The link validation function is called for |
| 321 | every link in the pipeline where both of the ends of the links are V4L2 |
| 322 | sub-devices. The driver is still responsible for validating the correctness |
| 323 | of the format configuration between sub-devices and video nodes. |
| 324 | |
| 325 | If link_validate op is not set, the default function |
| 326 | v4l2_subdev_link_validate_default() is used instead. This function ensures |
| 327 | that width, height and the media bus pixel code are equal on both source and |
| 328 | sink of the link. Subdev drivers are also free to use this function to |
| 329 | perform the checks mentioned above in addition to their own checks. |
| 330 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 331 | A device (bridge) driver needs to register the v4l2_subdev with the |
| 332 | v4l2_device: |
| 333 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 334 | int err = v4l2_device_register_subdev(v4l2_dev, sd); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 335 | |
| 336 | This can fail if the subdev module disappeared before it could be registered. |
| 337 | After this function was called successfully the subdev->dev field points to |
| 338 | the v4l2_device. |
| 339 | |
Laurent Pinchart | 61f5db5 | 2009-12-09 08:40:08 -0300 | [diff] [blame] | 340 | If the v4l2_device parent device has a non-NULL mdev field, the sub-device |
| 341 | entity will be automatically registered with the media device. |
| 342 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 343 | You can unregister a sub-device using: |
| 344 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 345 | v4l2_device_unregister_subdev(sd); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 346 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 347 | Afterwards the subdev module can be unloaded and sd->dev == NULL. |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 348 | |
| 349 | You can call an ops function either directly: |
| 350 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 351 | err = sd->ops->core->g_chip_ident(sd, &chip); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 352 | |
| 353 | but it is better and easier to use this macro: |
| 354 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 355 | err = v4l2_subdev_call(sd, core, g_chip_ident, &chip); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 356 | |
| 357 | The macro will to the right NULL pointer checks and returns -ENODEV if subdev |
| 358 | is NULL, -ENOIOCTLCMD if either subdev->core or subdev->core->g_chip_ident is |
| 359 | NULL, or the actual result of the subdev->ops->core->g_chip_ident ops. |
| 360 | |
| 361 | It is also possible to call all or a subset of the sub-devices: |
| 362 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 363 | v4l2_device_call_all(v4l2_dev, 0, core, g_chip_ident, &chip); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 364 | |
| 365 | Any subdev that does not support this ops is skipped and error results are |
| 366 | ignored. If you want to check for errors use this: |
| 367 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 368 | err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_chip_ident, &chip); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 369 | |
| 370 | Any error except -ENOIOCTLCMD will exit the loop with that error. If no |
Lucas De Marchi | 25985ed | 2011-03-30 22:57:33 -0300 | [diff] [blame] | 371 | errors (except -ENOIOCTLCMD) occurred, then 0 is returned. |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 372 | |
| 373 | The second argument to both calls is a group ID. If 0, then all subdevs are |
| 374 | called. If non-zero, then only those whose group ID match that value will |
Hans Verkuil | b016760 | 2009-02-14 12:00:53 -0300 | [diff] [blame] | 375 | be called. Before a bridge driver registers a subdev it can set sd->grp_id |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 376 | to whatever value it wants (it's 0 by default). This value is owned by the |
| 377 | bridge driver and the sub-device driver will never modify or use it. |
| 378 | |
| 379 | The group ID gives the bridge driver more control how callbacks are called. |
| 380 | For example, there may be multiple audio chips on a board, each capable of |
| 381 | changing the volume. But usually only one will actually be used when the |
| 382 | user want to change the volume. You can set the group ID for that subdev to |
| 383 | e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling |
| 384 | v4l2_device_call_all(). That ensures that it will only go to the subdev |
| 385 | that needs it. |
| 386 | |
Hans Verkuil | 98ec633 | 2009-03-08 17:02:10 -0300 | [diff] [blame] | 387 | If the sub-device needs to notify its v4l2_device parent of an event, then |
| 388 | it can call v4l2_subdev_notify(sd, notification, arg). This macro checks |
| 389 | whether there is a notify() callback defined and returns -ENODEV if not. |
| 390 | Otherwise the result of the notify() call is returned. |
| 391 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 392 | The advantage of using v4l2_subdev is that it is a generic struct and does |
| 393 | not contain any knowledge about the underlying hardware. So a driver might |
| 394 | contain several subdevs that use an I2C bus, but also a subdev that is |
| 395 | controlled through GPIO pins. This distinction is only relevant when setting |
| 396 | up the device, but once the subdev is registered it is completely transparent. |
| 397 | |
| 398 | |
Laurent Pinchart | 2096a5d | 2009-12-09 08:38:49 -0300 | [diff] [blame] | 399 | V4L2 sub-device userspace API |
| 400 | ----------------------------- |
| 401 | |
| 402 | Beside exposing a kernel API through the v4l2_subdev_ops structure, V4L2 |
| 403 | sub-devices can also be controlled directly by userspace applications. |
| 404 | |
| 405 | Device nodes named v4l-subdevX can be created in /dev to access sub-devices |
| 406 | directly. If a sub-device supports direct userspace configuration it must set |
| 407 | the V4L2_SUBDEV_FL_HAS_DEVNODE flag before being registered. |
| 408 | |
| 409 | After registering sub-devices, the v4l2_device driver can create device nodes |
| 410 | for all registered sub-devices marked with V4L2_SUBDEV_FL_HAS_DEVNODE by calling |
| 411 | v4l2_device_register_subdev_nodes(). Those device nodes will be automatically |
| 412 | removed when sub-devices are unregistered. |
| 413 | |
Laurent Pinchart | ea8aa43 | 2009-12-09 08:39:54 -0300 | [diff] [blame] | 414 | The device node handles a subset of the V4L2 API. |
| 415 | |
| 416 | VIDIOC_QUERYCTRL |
| 417 | VIDIOC_QUERYMENU |
| 418 | VIDIOC_G_CTRL |
| 419 | VIDIOC_S_CTRL |
| 420 | VIDIOC_G_EXT_CTRLS |
| 421 | VIDIOC_S_EXT_CTRLS |
| 422 | VIDIOC_TRY_EXT_CTRLS |
| 423 | |
| 424 | The controls ioctls are identical to the ones defined in V4L2. They |
| 425 | behave identically, with the only exception that they deal only with |
| 426 | controls implemented in the sub-device. Depending on the driver, those |
| 427 | controls can be also be accessed through one (or several) V4L2 device |
| 428 | nodes. |
| 429 | |
Sakari Ailus | 02adb1c | 2010-03-03 12:49:38 -0300 | [diff] [blame] | 430 | VIDIOC_DQEVENT |
| 431 | VIDIOC_SUBSCRIBE_EVENT |
| 432 | VIDIOC_UNSUBSCRIBE_EVENT |
| 433 | |
| 434 | The events ioctls are identical to the ones defined in V4L2. They |
| 435 | behave identically, with the only exception that they deal only with |
| 436 | events generated by the sub-device. Depending on the driver, those |
| 437 | events can also be reported by one (or several) V4L2 device nodes. |
| 438 | |
| 439 | Sub-device drivers that want to use events need to set the |
| 440 | V4L2_SUBDEV_USES_EVENTS v4l2_subdev::flags and initialize |
| 441 | v4l2_subdev::nevents to events queue depth before registering the |
| 442 | sub-device. After registration events can be queued as usual on the |
| 443 | v4l2_subdev::devnode device node. |
| 444 | |
| 445 | To properly support events, the poll() file operation is also |
| 446 | implemented. |
| 447 | |
Laurent Pinchart | c30b46e | 2010-02-26 12:23:10 -0300 | [diff] [blame] | 448 | Private ioctls |
| 449 | |
| 450 | All ioctls not in the above list are passed directly to the sub-device |
| 451 | driver through the core::ioctl operation. |
| 452 | |
Laurent Pinchart | 2096a5d | 2009-12-09 08:38:49 -0300 | [diff] [blame] | 453 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 454 | I2C sub-device drivers |
| 455 | ---------------------- |
| 456 | |
| 457 | Since these drivers are so common, special helper functions are available to |
| 458 | ease the use of these drivers (v4l2-common.h). |
| 459 | |
| 460 | The recommended method of adding v4l2_subdev support to an I2C driver is to |
| 461 | embed the v4l2_subdev struct into the state struct that is created for each |
| 462 | I2C device instance. Very simple devices have no state struct and in that case |
| 463 | you can just create a v4l2_subdev directly. |
| 464 | |
| 465 | A typical state struct would look like this (where 'chipname' is replaced by |
| 466 | the name of the chip): |
| 467 | |
| 468 | struct chipname_state { |
| 469 | struct v4l2_subdev sd; |
| 470 | ... /* additional state fields */ |
| 471 | }; |
| 472 | |
| 473 | Initialize the v4l2_subdev struct as follows: |
| 474 | |
| 475 | v4l2_i2c_subdev_init(&state->sd, client, subdev_ops); |
| 476 | |
| 477 | This function will fill in all the fields of v4l2_subdev and ensure that the |
| 478 | v4l2_subdev and i2c_client both point to one another. |
| 479 | |
| 480 | You should also add a helper inline function to go from a v4l2_subdev pointer |
| 481 | to a chipname_state struct: |
| 482 | |
| 483 | static inline struct chipname_state *to_state(struct v4l2_subdev *sd) |
| 484 | { |
| 485 | return container_of(sd, struct chipname_state, sd); |
| 486 | } |
| 487 | |
| 488 | Use this to go from the v4l2_subdev struct to the i2c_client struct: |
| 489 | |
| 490 | struct i2c_client *client = v4l2_get_subdevdata(sd); |
| 491 | |
| 492 | And this to go from an i2c_client to a v4l2_subdev struct: |
| 493 | |
| 494 | struct v4l2_subdev *sd = i2c_get_clientdata(client); |
| 495 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 496 | Make sure to call v4l2_device_unregister_subdev(sd) when the remove() callback |
| 497 | is called. This will unregister the sub-device from the bridge driver. It is |
| 498 | safe to call this even if the sub-device was never registered. |
| 499 | |
Hans Verkuil | f5360bd | 2009-01-15 06:09:05 -0300 | [diff] [blame] | 500 | You need to do this because when the bridge driver destroys the i2c adapter |
| 501 | the remove() callbacks are called of the i2c devices on that adapter. |
| 502 | After that the corresponding v4l2_subdev structures are invalid, so they |
| 503 | have to be unregistered first. Calling v4l2_device_unregister_subdev(sd) |
| 504 | from the remove() callback ensures that this is always done correctly. |
| 505 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 506 | |
| 507 | The bridge driver also has some helper functions it can use: |
| 508 | |
Hans Verkuil | e6574f2 | 2009-04-01 03:57:53 -0300 | [diff] [blame] | 509 | struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter, |
Hans Verkuil | 53dacb1 | 2009-08-10 02:49:08 -0300 | [diff] [blame] | 510 | "module_foo", "chipid", 0x36, NULL); |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 511 | |
| 512 | This loads the given module (can be NULL if no module needs to be loaded) and |
| 513 | calls i2c_new_device() with the given i2c_adapter and chip/address arguments. |
Hans Verkuil | e6574f2 | 2009-04-01 03:57:53 -0300 | [diff] [blame] | 514 | If all goes well, then it registers the subdev with the v4l2_device. |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 515 | |
Hans Verkuil | 53dacb1 | 2009-08-10 02:49:08 -0300 | [diff] [blame] | 516 | You can also use the last argument of v4l2_i2c_new_subdev() to pass an array |
| 517 | of possible I2C addresses that it should probe. These probe addresses are |
| 518 | only used if the previous argument is 0. A non-zero argument means that you |
| 519 | know the exact i2c address so in that case no probing will take place. |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 520 | |
| 521 | Both functions return NULL if something went wrong. |
| 522 | |
Hans Verkuil | 53dacb1 | 2009-08-10 02:49:08 -0300 | [diff] [blame] | 523 | Note that the chipid you pass to v4l2_i2c_new_subdev() is usually |
Hans Verkuil | 2c79252 | 2009-03-12 18:34:19 -0300 | [diff] [blame] | 524 | the same as the module name. It allows you to specify a chip variant, e.g. |
| 525 | "saa7114" or "saa7115". In general though the i2c driver autodetects this. |
| 526 | The use of chipid is something that needs to be looked at more closely at a |
| 527 | later date. It differs between i2c drivers and as such can be confusing. |
| 528 | To see which chip variants are supported you can look in the i2c driver code |
| 529 | for the i2c_device_id table. This lists all the possibilities. |
| 530 | |
Hans Verkuil | 2c0b19a | 2009-06-09 17:29:29 -0300 | [diff] [blame] | 531 | There are two more helper functions: |
| 532 | |
| 533 | v4l2_i2c_new_subdev_cfg: this function adds new irq and platform_data |
| 534 | arguments and has both 'addr' and 'probed_addrs' arguments: if addr is not |
| 535 | 0 then that will be used (non-probing variant), otherwise the probed_addrs |
| 536 | are probed. |
| 537 | |
| 538 | For example: this will probe for address 0x10: |
| 539 | |
| 540 | struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter, |
| 541 | "module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10)); |
| 542 | |
| 543 | v4l2_i2c_new_subdev_board uses an i2c_board_info struct which is passed |
| 544 | to the i2c driver and replaces the irq, platform_data and addr arguments. |
| 545 | |
| 546 | If the subdev supports the s_config core ops, then that op is called with |
| 547 | the irq and platform_data arguments after the subdev was setup. The older |
| 548 | v4l2_i2c_new_(probed_)subdev functions will call s_config as well, but with |
| 549 | irq set to 0 and platform_data set to NULL. |
| 550 | |
Hans Verkuil | 2a1fcdf | 2008-11-29 21:36:58 -0300 | [diff] [blame] | 551 | struct video_device |
| 552 | ------------------- |
| 553 | |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 554 | The actual device nodes in the /dev directory are created using the |
| 555 | video_device struct (v4l2-dev.h). This struct can either be allocated |
| 556 | dynamically or embedded in a larger struct. |
| 557 | |
| 558 | To allocate it dynamically use: |
| 559 | |
| 560 | struct video_device *vdev = video_device_alloc(); |
| 561 | |
| 562 | if (vdev == NULL) |
| 563 | return -ENOMEM; |
| 564 | |
| 565 | vdev->release = video_device_release; |
| 566 | |
| 567 | If you embed it in a larger struct, then you must set the release() |
| 568 | callback to your own function: |
| 569 | |
| 570 | struct video_device *vdev = &my_vdev->vdev; |
| 571 | |
| 572 | vdev->release = my_vdev_release; |
| 573 | |
| 574 | The release callback must be set and it is called when the last user |
| 575 | of the video device exits. |
| 576 | |
| 577 | The default video_device_release() callback just calls kfree to free the |
| 578 | allocated memory. |
| 579 | |
| 580 | You should also set these fields: |
| 581 | |
Hans Verkuil | dfa9a5a | 2008-12-23 12:17:23 -0300 | [diff] [blame] | 582 | - v4l2_dev: set to the v4l2_device parent device. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 583 | |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 584 | - name: set to something descriptive and unique. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 585 | |
Hans Verkuil | d2210f9 | 2012-09-17 05:06:33 -0300 | [diff] [blame] | 586 | - vfl_dir: set this to VFL_DIR_RX for capture devices (VFL_DIR_RX has value 0, |
| 587 | so this is normally already the default), set to VFL_DIR_TX for output |
| 588 | devices and VFL_DIR_M2M for mem2mem (codec) devices. |
| 589 | |
Hans Verkuil | c7dd09d | 2008-12-23 13:42:25 -0300 | [diff] [blame] | 590 | - fops: set to the v4l2_file_operations struct. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 591 | |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 592 | - ioctl_ops: if you use the v4l2_ioctl_ops to simplify ioctl maintenance |
| 593 | (highly recommended to use this and it might become compulsory in the |
Hans Verkuil | d2210f9 | 2012-09-17 05:06:33 -0300 | [diff] [blame] | 594 | future!), then set this to your v4l2_ioctl_ops struct. The vfl_type and |
| 595 | vfl_dir fields are used to disable ops that do not match the type/dir |
| 596 | combination. E.g. VBI ops are disabled for non-VBI nodes, and output ops |
| 597 | are disabled for a capture device. This makes it possible to provide |
| 598 | just one v4l2_ioctl_ops struct for both vbi and video nodes. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 599 | |
Hans Verkuil | ee6869a | 2010-09-26 08:47:38 -0300 | [diff] [blame] | 600 | - lock: leave to NULL if you want to do all the locking in the driver. |
Hans Verkuil | 74f22c4 | 2012-05-14 12:54:27 -0300 | [diff] [blame] | 601 | Otherwise you give it a pointer to a struct mutex_lock and before the |
| 602 | unlocked_ioctl file operation is called this lock will be taken by the |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 603 | core and released afterwards. See the next section for more details. |
| 604 | |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 605 | - queue: a pointer to the struct vb2_queue associated with this device node. |
| 606 | If queue is non-NULL, and queue->lock is non-NULL, then queue->lock is |
| 607 | used for the queuing ioctls (VIDIOC_REQBUFS, CREATE_BUFS, QBUF, DQBUF, |
| 608 | QUERYBUF, PREPARE_BUF, STREAMON and STREAMOFF) instead of the lock above. |
| 609 | That way the vb2 queuing framework does not have to wait for other ioctls. |
| 610 | This queue pointer is also used by the vb2 helper functions to check for |
| 611 | queuing ownership (i.e. is the filehandle calling it allowed to do the |
| 612 | operation). |
| 613 | |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 614 | - prio: keeps track of the priorities. Used to implement VIDIOC_G/S_PRIORITY. |
| 615 | If left to NULL, then it will use the struct v4l2_prio_state in v4l2_device. |
| 616 | If you want to have a separate priority state per (group of) device node(s), |
| 617 | then you can point it to your own struct v4l2_prio_state. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 618 | |
Hans Verkuil | 0057596 | 2009-03-13 10:03:04 -0300 | [diff] [blame] | 619 | - parent: you only set this if v4l2_device was registered with NULL as |
| 620 | the parent device struct. This only happens in cases where one hardware |
| 621 | device has multiple PCI devices that all share the same v4l2_device core. |
| 622 | |
| 623 | The cx88 driver is an example of this: one core v4l2_device struct, but |
| 624 | it is used by both an raw video PCI device (cx8800) and a MPEG PCI device |
| 625 | (cx8802). Since the v4l2_device cannot be associated with a particular |
| 626 | PCI device it is setup without a parent device. But when the struct |
| 627 | video_device is setup you do know which parent PCI device to use. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 628 | |
Hans Verkuil | b1a873a | 2011-03-22 10:14:07 -0300 | [diff] [blame] | 629 | - flags: optional. Set to V4L2_FL_USE_FH_PRIO if you want to let the framework |
| 630 | handle the VIDIOC_G/S_PRIORITY ioctls. This requires that you use struct |
| 631 | v4l2_fh. Eventually this flag will disappear once all drivers use the core |
| 632 | priority handling. But for now it has to be set explicitly. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 633 | |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 634 | If you use v4l2_ioctl_ops, then you should set .unlocked_ioctl to video_ioctl2 |
| 635 | in your v4l2_file_operations struct. |
| 636 | |
| 637 | Do not use .ioctl! This is deprecated and will go away in the future. |
Hans Verkuil | c7dd09d | 2008-12-23 13:42:25 -0300 | [diff] [blame] | 638 | |
Hans Verkuil | 1dd8728 | 2012-05-10 05:04:41 -0300 | [diff] [blame] | 639 | In some cases you want to tell the core that a function you had specified in |
| 640 | your v4l2_ioctl_ops should be ignored. You can mark such ioctls by calling this |
| 641 | function before video_device_register is called: |
| 642 | |
Hans Verkuil | 152a3a7 | 2012-05-14 11:32:48 -0300 | [diff] [blame] | 643 | void v4l2_disable_ioctl(struct video_device *vdev, unsigned int cmd); |
Hans Verkuil | 1dd8728 | 2012-05-10 05:04:41 -0300 | [diff] [blame] | 644 | |
| 645 | This tends to be needed if based on external factors (e.g. which card is |
| 646 | being used) you want to turns off certain features in v4l2_ioctl_ops without |
| 647 | having to make a new struct. |
| 648 | |
Hans Verkuil | c7dd09d | 2008-12-23 13:42:25 -0300 | [diff] [blame] | 649 | The v4l2_file_operations struct is a subset of file_operations. The main |
| 650 | difference is that the inode argument is omitted since it is never used. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 651 | |
Laurent Pinchart | 2c0ab67 | 2009-12-09 08:40:10 -0300 | [diff] [blame] | 652 | If integration with the media framework is needed, you must initialize the |
| 653 | media_entity struct embedded in the video_device struct (entity field) by |
| 654 | calling media_entity_init(): |
| 655 | |
| 656 | struct media_pad *pad = &my_vdev->pad; |
| 657 | int err; |
| 658 | |
| 659 | err = media_entity_init(&vdev->entity, 1, pad, 0); |
| 660 | |
| 661 | The pads array must have been previously initialized. There is no need to |
| 662 | manually set the struct media_entity type and name fields. |
| 663 | |
| 664 | A reference to the entity will be automatically acquired/released when the |
| 665 | video device is opened/closed. |
| 666 | |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 667 | ioctls and locking |
| 668 | ------------------ |
Hans Verkuil | ee6869a | 2010-09-26 08:47:38 -0300 | [diff] [blame] | 669 | |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 670 | The V4L core provides optional locking services. The main service is the |
| 671 | lock field in struct video_device, which is a pointer to a mutex. If you set |
| 672 | this pointer, then that will be used by unlocked_ioctl to serialize all ioctls. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 673 | |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 674 | If you are using the videobuf2 framework, then there is a second lock that you |
| 675 | can set: video_device->queue->lock. If set, then this lock will be used instead |
| 676 | of video_device->lock to serialize all queuing ioctls (see the previous section |
| 677 | for the full list of those ioctls). |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 678 | |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 679 | The advantage of using a different lock for the queuing ioctls is that for some |
| 680 | drivers (particularly USB drivers) certain commands such as setting controls |
| 681 | can take a long time, so you want to use a separate lock for the buffer queuing |
| 682 | ioctls. That way your VIDIOC_DQBUF doesn't stall because the driver is busy |
| 683 | changing the e.g. exposure of the webcam. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 684 | |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 685 | Of course, you can always do all the locking yourself by leaving both lock |
| 686 | pointers at NULL. |
Hans Verkuil | 8ab75e3 | 2012-05-10 02:51:31 -0300 | [diff] [blame] | 687 | |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 688 | If you use the old videobuf then you must pass the video_device lock to the |
| 689 | videobuf queue initialize function: if videobuf has to wait for a frame to |
| 690 | arrive, then it will temporarily unlock the lock and relock it afterwards. If |
| 691 | your driver also waits in the code, then you should do the same to allow other |
| 692 | processes to access the device node while the first process is waiting for |
| 693 | something. |
Hans Verkuil | ee6869a | 2010-09-26 08:47:38 -0300 | [diff] [blame] | 694 | |
Hans Verkuil | 43599f3 | 2011-11-07 12:44:28 -0300 | [diff] [blame] | 695 | In the case of videobuf2 you will need to implement the wait_prepare and |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 696 | wait_finish callbacks to unlock/lock if applicable. If you use the queue->lock |
| 697 | pointer, then you can use the helper functions vb2_ops_wait_prepare/finish. |
Hans Verkuil | 43599f3 | 2011-11-07 12:44:28 -0300 | [diff] [blame] | 698 | |
Hans Verkuil | 4a77a83 | 2012-07-02 05:43:34 -0300 | [diff] [blame] | 699 | The implementation of a hotplug disconnect should also take the lock from |
| 700 | video_device before calling v4l2_device_disconnect. If you are also using |
| 701 | video_device->queue->lock, then you have to first lock video_device->queue->lock |
| 702 | followed by video_device->lock. That way you can be sure no ioctl is running |
| 703 | when you call v4l2_device_disconnect. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 704 | |
| 705 | video_device registration |
| 706 | ------------------------- |
| 707 | |
| 708 | Next you register the video device: this will create the character device |
| 709 | for you. |
| 710 | |
| 711 | err = video_register_device(vdev, VFL_TYPE_GRABBER, -1); |
| 712 | if (err) { |
Hans Verkuil | 50a2a8b | 2008-12-22 09:13:11 -0300 | [diff] [blame] | 713 | video_device_release(vdev); /* or kfree(my_vdev); */ |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 714 | return err; |
| 715 | } |
| 716 | |
Laurent Pinchart | 2c0ab67 | 2009-12-09 08:40:10 -0300 | [diff] [blame] | 717 | If the v4l2_device parent device has a non-NULL mdev field, the video device |
| 718 | entity will be automatically registered with the media device. |
| 719 | |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 720 | Which device is registered depends on the type argument. The following |
| 721 | types exist: |
| 722 | |
| 723 | VFL_TYPE_GRABBER: videoX for video input/output devices |
| 724 | VFL_TYPE_VBI: vbiX for vertical blank data (i.e. closed captions, teletext) |
| 725 | VFL_TYPE_RADIO: radioX for radio tuners |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 726 | |
| 727 | The last argument gives you a certain amount of control over the device |
Hans Verkuil | 6b5270d | 2009-09-06 07:54:00 -0300 | [diff] [blame] | 728 | device node number used (i.e. the X in videoX). Normally you will pass -1 |
| 729 | to let the v4l2 framework pick the first free number. But sometimes users |
| 730 | want to select a specific node number. It is common that drivers allow |
| 731 | the user to select a specific device node number through a driver module |
| 732 | option. That number is then passed to this function and video_register_device |
| 733 | will attempt to select that device node number. If that number was already |
| 734 | in use, then the next free device node number will be selected and it |
| 735 | will send a warning to the kernel log. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 736 | |
Hans Verkuil | 6b5270d | 2009-09-06 07:54:00 -0300 | [diff] [blame] | 737 | Another use-case is if a driver creates many devices. In that case it can |
| 738 | be useful to place different video devices in separate ranges. For example, |
| 739 | video capture devices start at 0, video output devices start at 16. |
Hans Verkuil | 22e2212 | 2009-09-06 07:13:14 -0300 | [diff] [blame] | 740 | So you can use the last argument to specify a minimum device node number |
| 741 | and the v4l2 framework will try to pick the first free number that is equal |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 742 | or higher to what you passed. If that fails, then it will just pick the |
| 743 | first free number. |
| 744 | |
Hans Verkuil | 6b5270d | 2009-09-06 07:54:00 -0300 | [diff] [blame] | 745 | Since in this case you do not care about a warning about not being able |
| 746 | to select the specified device node number, you can call the function |
| 747 | video_register_device_no_warn() instead. |
| 748 | |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 749 | Whenever a device node is created some attributes are also created for you. |
| 750 | If you look in /sys/class/video4linux you see the devices. Go into e.g. |
| 751 | video0 and you will see 'name' and 'index' attributes. The 'name' attribute |
Hans Verkuil | 7ae0cd9 | 2009-06-19 11:32:56 -0300 | [diff] [blame] | 752 | is the 'name' field of the video_device struct. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 753 | |
Hans Verkuil | 7ae0cd9 | 2009-06-19 11:32:56 -0300 | [diff] [blame] | 754 | The 'index' attribute is the index of the device node: for each call to |
| 755 | video_register_device() the index is just increased by 1. The first video |
| 756 | device node you register always starts with index 0. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 757 | |
| 758 | Users can setup udev rules that utilize the index attribute to make fancy |
| 759 | device names (e.g. 'mpegX' for MPEG video capture device nodes). |
| 760 | |
| 761 | After the device was successfully registered, then you can use these fields: |
| 762 | |
| 763 | - vfl_type: the device type passed to video_register_device. |
| 764 | - minor: the assigned device minor number. |
Hans Verkuil | 22e2212 | 2009-09-06 07:13:14 -0300 | [diff] [blame] | 765 | - num: the device node number (i.e. the X in videoX). |
Hans Verkuil | 7ae0cd9 | 2009-06-19 11:32:56 -0300 | [diff] [blame] | 766 | - index: the device index number. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 767 | |
| 768 | If the registration failed, then you need to call video_device_release() |
| 769 | to free the allocated video_device struct, or free your own struct if the |
| 770 | video_device was embedded in it. The vdev->release() callback will never |
| 771 | be called if the registration failed, nor should you ever attempt to |
| 772 | unregister the device if the registration failed. |
| 773 | |
| 774 | |
| 775 | video_device cleanup |
| 776 | -------------------- |
| 777 | |
| 778 | When the video device nodes have to be removed, either during the unload |
| 779 | of the driver or because the USB device was disconnected, then you should |
| 780 | unregister them: |
| 781 | |
| 782 | video_unregister_device(vdev); |
| 783 | |
| 784 | This will remove the device nodes from sysfs (causing udev to remove them |
| 785 | from /dev). |
| 786 | |
Hans Verkuil | dd1ad94 | 2010-04-06 11:44:39 -0300 | [diff] [blame] | 787 | After video_unregister_device() returns no new opens can be done. However, |
| 788 | in the case of USB devices some application might still have one of these |
Hans Verkuil | d69f271 | 2010-09-26 08:16:56 -0300 | [diff] [blame] | 789 | device nodes open. So after the unregister all file operations (except |
| 790 | release, of course) will return an error as well. |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 791 | |
| 792 | When the last user of the video device node exits, then the vdev->release() |
| 793 | callback is called and you can do the final cleanup there. |
| 794 | |
Laurent Pinchart | 2c0ab67 | 2009-12-09 08:40:10 -0300 | [diff] [blame] | 795 | Don't forget to cleanup the media entity associated with the video device if |
| 796 | it has been initialized: |
| 797 | |
| 798 | media_entity_cleanup(&vdev->entity); |
| 799 | |
| 800 | This can be done from the release callback. |
| 801 | |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 802 | |
| 803 | video_device helper functions |
| 804 | ----------------------------- |
| 805 | |
| 806 | There are a few useful helper functions: |
| 807 | |
Laurent Pinchart | eac8ea5 | 2009-11-27 13:56:50 -0300 | [diff] [blame] | 808 | - file/video_device private data |
| 809 | |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 810 | You can set/get driver private data in the video_device struct using: |
| 811 | |
Hans Verkuil | 89aec3e | 2009-02-07 07:07:04 -0300 | [diff] [blame] | 812 | void *video_get_drvdata(struct video_device *vdev); |
| 813 | void video_set_drvdata(struct video_device *vdev, void *data); |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 814 | |
| 815 | Note that you can safely call video_set_drvdata() before calling |
| 816 | video_register_device(). |
| 817 | |
| 818 | And this function: |
| 819 | |
| 820 | struct video_device *video_devdata(struct file *file); |
| 821 | |
| 822 | returns the video_device belonging to the file struct. |
| 823 | |
Laurent Pinchart | eac8ea5 | 2009-11-27 13:56:50 -0300 | [diff] [blame] | 824 | The video_drvdata function combines video_get_drvdata with video_devdata: |
Hans Verkuil | a47ddf1 | 2008-12-19 10:20:22 -0300 | [diff] [blame] | 825 | |
| 826 | void *video_drvdata(struct file *file); |
| 827 | |
| 828 | You can go from a video_device struct to the v4l2_device struct using: |
| 829 | |
Hans Verkuil | dfa9a5a | 2008-12-23 12:17:23 -0300 | [diff] [blame] | 830 | struct v4l2_device *v4l2_dev = vdev->v4l2_dev; |
Mauro Carvalho Chehab | 44061c0 | 2009-02-14 07:29:07 -0300 | [diff] [blame] | 831 | |
Laurent Pinchart | eac8ea5 | 2009-11-27 13:56:50 -0300 | [diff] [blame] | 832 | - Device node name |
| 833 | |
| 834 | The video_device node kernel name can be retrieved using |
| 835 | |
| 836 | const char *video_device_node_name(struct video_device *vdev); |
| 837 | |
| 838 | The name is used as a hint by userspace tools such as udev. The function |
| 839 | should be used where possible instead of accessing the video_device::num and |
| 840 | video_device::minor fields. |
| 841 | |
| 842 | |
Mauro Carvalho Chehab | 44061c0 | 2009-02-14 07:29:07 -0300 | [diff] [blame] | 843 | video buffer helper functions |
| 844 | ----------------------------- |
| 845 | |
Jonathan Corbet | 4b586a3 | 2010-02-22 17:47:46 -0300 | [diff] [blame] | 846 | The v4l2 core API provides a set of standard methods (called "videobuf") |
| 847 | for dealing with video buffers. Those methods allow a driver to implement |
| 848 | read(), mmap() and overlay() in a consistent way. There are currently |
| 849 | methods for using video buffers on devices that supports DMA with |
| 850 | scatter/gather method (videobuf-dma-sg), DMA with linear access |
| 851 | (videobuf-dma-contig), and vmalloced buffers, mostly used on USB drivers |
| 852 | (videobuf-vmalloc). |
Mauro Carvalho Chehab | 44061c0 | 2009-02-14 07:29:07 -0300 | [diff] [blame] | 853 | |
Jonathan Corbet | 4b586a3 | 2010-02-22 17:47:46 -0300 | [diff] [blame] | 854 | Please see Documentation/video4linux/videobuf for more information on how |
| 855 | to use the videobuf layer. |
Sakari Ailus | 6cd84b7 | 2010-03-20 18:28:48 -0300 | [diff] [blame] | 856 | |
| 857 | struct v4l2_fh |
| 858 | -------------- |
| 859 | |
| 860 | struct v4l2_fh provides a way to easily keep file handle specific data |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 861 | that is used by the V4L2 framework. New drivers must use struct v4l2_fh |
Hans Verkuil | b1a873a | 2011-03-22 10:14:07 -0300 | [diff] [blame] | 862 | since it is also used to implement priority handling (VIDIOC_G/S_PRIORITY) |
| 863 | if the video_device flag V4L2_FL_USE_FH_PRIO is also set. |
Sakari Ailus | 6cd84b7 | 2010-03-20 18:28:48 -0300 | [diff] [blame] | 864 | |
| 865 | The users of v4l2_fh (in the V4L2 framework, not the driver) know |
| 866 | whether a driver uses v4l2_fh as its file->private_data pointer by |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 867 | testing the V4L2_FL_USES_V4L2_FH bit in video_device->flags. This bit is |
| 868 | set whenever v4l2_fh_init() is called. |
Sakari Ailus | 6cd84b7 | 2010-03-20 18:28:48 -0300 | [diff] [blame] | 869 | |
| 870 | struct v4l2_fh is allocated as a part of the driver's own file handle |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 871 | structure and file->private_data is set to it in the driver's open |
| 872 | function by the driver. |
| 873 | |
| 874 | In many cases the struct v4l2_fh will be embedded in a larger structure. |
| 875 | In that case you should call v4l2_fh_init+v4l2_fh_add in open() and |
| 876 | v4l2_fh_del+v4l2_fh_exit in release(). |
| 877 | |
| 878 | Drivers can extract their own file handle structure by using the container_of |
| 879 | macro. Example: |
Sakari Ailus | 6cd84b7 | 2010-03-20 18:28:48 -0300 | [diff] [blame] | 880 | |
| 881 | struct my_fh { |
| 882 | int blah; |
| 883 | struct v4l2_fh fh; |
| 884 | }; |
| 885 | |
| 886 | ... |
| 887 | |
| 888 | int my_open(struct file *file) |
| 889 | { |
| 890 | struct my_fh *my_fh; |
| 891 | struct video_device *vfd; |
| 892 | int ret; |
| 893 | |
| 894 | ... |
| 895 | |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 896 | my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL); |
Sakari Ailus | 6cd84b7 | 2010-03-20 18:28:48 -0300 | [diff] [blame] | 897 | |
| 898 | ... |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 899 | |
Hans Verkuil | 98019f5 | 2011-06-18 05:13:55 -0300 | [diff] [blame] | 900 | v4l2_fh_init(&my_fh->fh, vfd); |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 901 | |
| 902 | ... |
| 903 | |
| 904 | file->private_data = &my_fh->fh; |
| 905 | v4l2_fh_add(&my_fh->fh); |
| 906 | return 0; |
Sakari Ailus | 6cd84b7 | 2010-03-20 18:28:48 -0300 | [diff] [blame] | 907 | } |
| 908 | |
| 909 | int my_release(struct file *file) |
| 910 | { |
| 911 | struct v4l2_fh *fh = file->private_data; |
| 912 | struct my_fh *my_fh = container_of(fh, struct my_fh, fh); |
| 913 | |
| 914 | ... |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 915 | v4l2_fh_del(&my_fh->fh); |
| 916 | v4l2_fh_exit(&my_fh->fh); |
| 917 | kfree(my_fh); |
| 918 | return 0; |
Sakari Ailus | 6cd84b7 | 2010-03-20 18:28:48 -0300 | [diff] [blame] | 919 | } |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 920 | |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 921 | Below is a short description of the v4l2_fh functions used: |
| 922 | |
Hans Verkuil | 98019f5 | 2011-06-18 05:13:55 -0300 | [diff] [blame] | 923 | void v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev) |
Hans Verkuil | 6e29ad5 | 2011-02-24 10:58:13 -0300 | [diff] [blame] | 924 | |
| 925 | Initialise the file handle. This *MUST* be performed in the driver's |
| 926 | v4l2_file_operations->open() handler. |
| 927 | |
| 928 | void v4l2_fh_add(struct v4l2_fh *fh) |
| 929 | |
| 930 | Add a v4l2_fh to video_device file handle list. Must be called once the |
| 931 | file handle is completely initialized. |
| 932 | |
| 933 | void v4l2_fh_del(struct v4l2_fh *fh) |
| 934 | |
| 935 | Unassociate the file handle from video_device(). The file handle |
| 936 | exit function may now be called. |
| 937 | |
| 938 | void v4l2_fh_exit(struct v4l2_fh *fh) |
| 939 | |
| 940 | Uninitialise the file handle. After uninitialisation the v4l2_fh |
| 941 | memory can be freed. |
| 942 | |
| 943 | |
| 944 | If struct v4l2_fh is not embedded, then you can use these helper functions: |
| 945 | |
| 946 | int v4l2_fh_open(struct file *filp) |
| 947 | |
| 948 | This allocates a struct v4l2_fh, initializes it and adds it to the struct |
| 949 | video_device associated with the file struct. |
| 950 | |
| 951 | int v4l2_fh_release(struct file *filp) |
| 952 | |
| 953 | This deletes it from the struct video_device associated with the file |
| 954 | struct, uninitialised the v4l2_fh and frees it. |
| 955 | |
| 956 | These two functions can be plugged into the v4l2_file_operation's open() and |
| 957 | release() ops. |
| 958 | |
| 959 | |
| 960 | Several drivers need to do something when the first file handle is opened and |
| 961 | when the last file handle closes. Two helper functions were added to check |
| 962 | whether the v4l2_fh struct is the only open filehandle of the associated |
| 963 | device node: |
| 964 | |
| 965 | int v4l2_fh_is_singular(struct v4l2_fh *fh) |
| 966 | |
| 967 | Returns 1 if the file handle is the only open file handle, else 0. |
| 968 | |
| 969 | int v4l2_fh_is_singular_file(struct file *filp) |
| 970 | |
| 971 | Same, but it calls v4l2_fh_is_singular with filp->private_data. |
| 972 | |
| 973 | |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 974 | V4L2 events |
| 975 | ----------- |
| 976 | |
| 977 | The V4L2 events provide a generic way to pass events to user space. |
| 978 | The driver must use v4l2_fh to be able to support V4L2 events. |
| 979 | |
Hans Verkuil | 1de7310 | 2011-06-18 06:14:42 -0300 | [diff] [blame] | 980 | Events are defined by a type and an optional ID. The ID may refer to a V4L2 |
| 981 | object such as a control ID. If unused, then the ID is 0. |
| 982 | |
| 983 | When the user subscribes to an event the driver will allocate a number of |
| 984 | kevent structs for that event. So every (type, ID) event tuple will have |
| 985 | its own set of kevent structs. This guarantees that if a driver is generating |
| 986 | lots of events of one type in a short time, then that will not overwrite |
| 987 | events of another type. |
| 988 | |
| 989 | But if you get more events of one type than the number of kevents that were |
| 990 | reserved, then the oldest event will be dropped and the new one added. |
| 991 | |
| 992 | Furthermore, the internal struct v4l2_subscribed_event has merge() and |
| 993 | replace() callbacks which drivers can set. These callbacks are called when |
| 994 | a new event is raised and there is no more room. The replace() callback |
| 995 | allows you to replace the payload of the old event with that of the new event, |
| 996 | merging any relevant data from the old payload into the new payload that |
| 997 | replaces it. It is called when this event type has only one kevent struct |
| 998 | allocated. The merge() callback allows you to merge the oldest event payload |
| 999 | into that of the second-oldest event payload. It is called when there are two |
| 1000 | or more kevent structs allocated. |
| 1001 | |
| 1002 | This way no status information is lost, just the intermediate steps leading |
| 1003 | up to that state. |
| 1004 | |
| 1005 | A good example of these replace/merge callbacks is in v4l2-event.c: |
| 1006 | ctrls_replace() and ctrls_merge() callbacks for the control event. |
| 1007 | |
| 1008 | Note: these callbacks can be called from interrupt context, so they must be |
| 1009 | fast. |
| 1010 | |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 1011 | Useful functions: |
| 1012 | |
Hans de Goede | c53c254 | 2012-04-08 12:59:46 -0300 | [diff] [blame] | 1013 | void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev) |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 1014 | |
| 1015 | Queue events to video device. The driver's only responsibility is to fill |
| 1016 | in the type and the data fields. The other fields will be filled in by |
| 1017 | V4L2. |
| 1018 | |
Hans de Goede | c53c254 | 2012-04-08 12:59:46 -0300 | [diff] [blame] | 1019 | int v4l2_event_subscribe(struct v4l2_fh *fh, |
| 1020 | struct v4l2_event_subscription *sub, unsigned elems, |
| 1021 | const struct v4l2_subscribed_event_ops *ops) |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 1022 | |
| 1023 | The video_device->ioctl_ops->vidioc_subscribe_event must check the driver |
| 1024 | is able to produce events with specified event id. Then it calls |
Hans de Goede | c53c254 | 2012-04-08 12:59:46 -0300 | [diff] [blame] | 1025 | v4l2_event_subscribe() to subscribe the event. |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 1026 | |
Hans de Goede | c53c254 | 2012-04-08 12:59:46 -0300 | [diff] [blame] | 1027 | The elems argument is the size of the event queue for this event. If it is 0, |
| 1028 | then the framework will fill in a default value (this depends on the event |
| 1029 | type). |
| 1030 | |
| 1031 | The ops argument allows the driver to specify a number of callbacks: |
| 1032 | * add: called when a new listener gets added (subscribing to the same |
| 1033 | event twice will only cause this callback to get called once) |
| 1034 | * del: called when a listener stops listening |
| 1035 | * replace: replace event 'old' with event 'new'. |
| 1036 | * merge: merge event 'old' into event 'new'. |
| 1037 | All 4 callbacks are optional, if you don't want to specify any callbacks |
| 1038 | the ops argument itself maybe NULL. |
| 1039 | |
| 1040 | int v4l2_event_unsubscribe(struct v4l2_fh *fh, |
| 1041 | struct v4l2_event_subscription *sub) |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 1042 | |
| 1043 | vidioc_unsubscribe_event in struct v4l2_ioctl_ops. A driver may use |
| 1044 | v4l2_event_unsubscribe() directly unless it wants to be involved in |
| 1045 | unsubscription process. |
| 1046 | |
| 1047 | The special type V4L2_EVENT_ALL may be used to unsubscribe all events. The |
| 1048 | drivers may want to handle this in a special way. |
| 1049 | |
Hans de Goede | c53c254 | 2012-04-08 12:59:46 -0300 | [diff] [blame] | 1050 | int v4l2_event_pending(struct v4l2_fh *fh) |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 1051 | |
| 1052 | Returns the number of pending events. Useful when implementing poll. |
| 1053 | |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 1054 | Events are delivered to user space through the poll system call. The driver |
Hans Verkuil | 1de7310 | 2011-06-18 06:14:42 -0300 | [diff] [blame] | 1055 | can use v4l2_fh->wait (a wait_queue_head_t) as the argument for poll_wait(). |
Sakari Ailus | dd96608 | 2010-03-27 10:58:24 -0300 | [diff] [blame] | 1056 | |
| 1057 | There are standard and private events. New standard events must use the |
| 1058 | smallest available event type. The drivers must allocate their events from |
| 1059 | their own class starting from class base. Class base is |
| 1060 | V4L2_EVENT_PRIVATE_START + n * 1000 where n is the lowest available number. |
| 1061 | The first event type in the class is reserved for future use, so the first |
| 1062 | available event type is 'class base + 1'. |
| 1063 | |
| 1064 | An example on how the V4L2 events may be used can be found in the OMAP |
Lad, Prabhakar | 83c7353 | 2012-09-14 05:17:52 -0300 | [diff] [blame] | 1065 | 3 ISP driver (drivers/media/platform/omap3isp). |