1.7. V4L2 sub-devices

Many drivers need to communicate with sub-devices. These devices can do all sort of tasks, but most commonly they handle audio and/or video muxing, encoding or decoding. For webcams common sub-devices are sensors and camera controllers.

Usually these are I2C devices, but not necessarily. In order to provide the driver with a consistent interface to these sub-devices the v4l2_subdev struct (v4l2-subdev.h) was created.

Each sub-device driver must have a v4l2_subdev struct. This struct can be stand-alone for simple sub-devices or it might be embedded in a larger struct if more state information needs to be stored. Usually there is a low-level device struct (e.g. i2c_client) that contains the device data as setup by the kernel. It is recommended to store that pointer in the private data of v4l2_subdev using v4l2_set_subdevdata(). That makes it easy to go from a v4l2_subdev to the actual low-level bus-specific device data.

You also need a way to go from the low-level struct to v4l2_subdev. For the common i2c_client struct the i2c_set_clientdata() call is used to store a v4l2_subdev pointer, for other busses you may have to use other methods.

Bridges might also need to store per-subdev private data, such as a pointer to bridge-specific per-subdev private data. The v4l2_subdev structure provides host private data for that purpose that can be accessed with v4l2_get_subdev_hostdata() and v4l2_set_subdev_hostdata().

From the bridge driver perspective, you load the sub-device module and somehow obtain the v4l2_subdev pointer. For i2c devices this is easy: you call i2c_get_clientdata(). For other busses something similar needs to be done. Helper functions exists for sub-devices on an I2C bus that do most of this tricky work for you.

Each v4l2_subdev contains function pointers that sub-device drivers can implement (or leave NULL if it is not applicable). Since sub-devices can do so many different things and you do not want to end up with a huge ops struct of which only a handful of ops are commonly implemented, the function pointers are sorted according to category and each category has its own ops struct.

The top-level ops struct contains pointers to the category ops structs, which may be NULL if the subdev driver does not support anything from that category.

It looks like this:

struct v4l2_subdev_core_ops {
        int (*log_status)(struct v4l2_subdev *sd);
        int (*init)(struct v4l2_subdev *sd, u32 val);

struct v4l2_subdev_tuner_ops {

struct v4l2_subdev_audio_ops {

struct v4l2_subdev_video_ops {

struct v4l2_subdev_pad_ops {

struct v4l2_subdev_ops {
        const struct v4l2_subdev_core_ops  *core;
        const struct v4l2_subdev_tuner_ops *tuner;
        const struct v4l2_subdev_audio_ops *audio;
        const struct v4l2_subdev_video_ops *video;
        const struct v4l2_subdev_pad_ops *video;

The core ops are common to all subdevs, the other categories are implemented depending on the sub-device. E.g. a video device is unlikely to support the audio ops and vice versa.

This setup limits the number of function pointers while still making it easy to add new ops and categories.

A sub-device driver initializes the v4l2_subdev struct using:

Afterwards you need to initialize sd->name with a unique name and set the module owner. This is done for you if you use the i2c helper functions.

If integration with the media framework is needed, you must initialize the media_entity struct embedded in the v4l2_subdev struct (entity field) by calling media_entity_pads_init(), if the entity has pads:

struct media_pad *pads = &my_sd->pads;
int err;

err = media_entity_pads_init(&sd->entity, npads, pads);

The pads array must have been previously initialized. There is no need to manually set the struct media_entity function and name fields, but the revision field must be initialized if needed.

A reference to the entity will be automatically acquired/released when the subdev device node (if any) is opened/closed.

Don’t forget to cleanup the media entity before the sub-device is destroyed:


If the subdev driver intends to process video and integrate with the media framework, it must implement format related functionality using v4l2_subdev_pad_ops instead of v4l2_subdev_video_ops.

In that case, the subdev driver may set the link_validate field to provide its own link validation function. The link validation function is called for every link in the pipeline where both of the ends of the links are V4L2 sub-devices. The driver is still responsible for validating the correctness of the format configuration between sub-devices and video nodes.

If link_validate op is not set, the default function v4l2_subdev_link_validate_default() is used instead. This function ensures that width, height and the media bus pixel code are equal on both source and sink of the link. Subdev drivers are also free to use this function to perform the checks mentioned above in addition to their own checks.

There are currently two ways to register subdevices with the V4L2 core. The first (traditional) possibility is to have subdevices registered by bridge drivers. This can be done when the bridge driver has the complete information about subdevices connected to it and knows exactly when to register them. This is typically the case for internal subdevices, like video data processing units within SoCs or complex PCI(e) boards, camera sensors in USB cameras or connected to SoCs, which pass information about them to bridge drivers, usually in their platform data.

There are however also situations where subdevices have to be registered asynchronously to bridge devices. An example of such a configuration is a Device Tree based system where information about subdevices is made available to the system independently from the bridge devices, e.g. when subdevices are defined in DT as I2C device nodes. The API used in this second case is described further below.

Using one or the other registration method only affects the probing process, the run-time bridge-subdevice interaction is in both cases the same.

In the synchronous case a device (bridge) driver needs to register the v4l2_subdev with the v4l2_device:

This can fail if the subdev module disappeared before it could be registered. After this function was called successfully the subdev->dev field points to the v4l2_device.

If the v4l2_device parent device has a non-NULL mdev field, the sub-device entity will be automatically registered with the media device.

You can unregister a sub-device using:

Afterwards the subdev module can be unloaded and sd->dev == NULL.

You can call an ops function either directly:

err = sd->ops->core->g_std(sd, &norm);

but it is better and easier to use this macro:

err = v4l2_subdev_call(sd, core, g_std, &norm);

The macro will to the right NULL pointer checks and returns -ENODEV if sd is NULL, -ENOIOCTLCMD if either sd->core or sd->core->g_std is NULL, or the actual result of the sd->ops->core->g_std ops.

It is also possible to call all or a subset of the sub-devices:

v4l2_device_call_all(v4l2_dev, 0, core, g_std, &norm);

Any subdev that does not support this ops is skipped and error results are ignored. If you want to check for errors use this:

err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_std, &norm);

Any error except -ENOIOCTLCMD will exit the loop with that error. If no errors (except -ENOIOCTLCMD) occurred, then 0 is returned.

The second argument to both calls is a group ID. If 0, then all subdevs are called. If non-zero, then only those whose group ID match that value will be called. Before a bridge driver registers a subdev it can set sd->grp_id to whatever value it wants (it’s 0 by default). This value is owned by the bridge driver and the sub-device driver will never modify or use it.

The group ID gives the bridge driver more control how callbacks are called. For example, there may be multiple audio chips on a board, each capable of changing the volume. But usually only one will actually be used when the user want to change the volume. You can set the group ID for that subdev to e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling v4l2_device_call_all(). That ensures that it will only go to the subdev that needs it.

If the sub-device needs to notify its v4l2_device parent of an event, then it can call v4l2_subdev_notify(sd, notification, arg). This macro checks whether there is a notify() callback defined and returns -ENODEV if not. Otherwise the result of the notify() call is returned.

The advantage of using v4l2_subdev is that it is a generic struct and does not contain any knowledge about the underlying hardware. So a driver might contain several subdevs that use an I2C bus, but also a subdev that is controlled through GPIO pins. This distinction is only relevant when setting up the device, but once the subdev is registered it is completely transparent.

In the asynchronous case subdevice probing can be invoked independently of the bridge driver availability. The subdevice driver then has to verify whether all the requirements for a successful probing are satisfied. This can include a check for a master clock availability. If any of the conditions aren’t satisfied the driver might decide to return -EPROBE_DEFER to request further reprobing attempts. Once all conditions are met the subdevice shall be registered using the v4l2_async_register_subdev() function. Unregistration is performed using the v4l2_async_unregister_subdev() call. Subdevices registered this way are stored in a global list of subdevices, ready to be picked up by bridge drivers.

Bridge drivers in turn have to register a notifier object with an array of subdevice descriptors that the bridge device needs for its operation. This is performed using the v4l2_async_notifier_register() call. To unregister the notifier the driver has to call v4l2_async_notifier_unregister(). The former of the two functions takes two arguments: a pointer to struct v4l2_device and a pointer to struct v4l2_async_notifier. The latter contains a pointer to an array of pointers to subdevice descriptors of type struct v4l2_async_subdev type. The V4L2 core will then use these descriptors to match asynchronously registered subdevices to them. If a match is detected the .bound() notifier callback is called. After all subdevices have been located the .complete() callback is called. When a subdevice is removed from the system the .unbind() method is called. All three callbacks are optional.

1.8. V4L2 sub-device userspace API

Beside exposing a kernel API through the v4l2_subdev_ops structure, V4L2 sub-devices can also be controlled directly by userspace applications.

Device nodes named v4l-subdevX can be created in /dev to access sub-devices directly. If a sub-device supports direct userspace configuration it must set the V4L2_SUBDEV_FL_HAS_DEVNODE flag before being registered.

After registering sub-devices, the v4l2_device driver can create device nodes for all registered sub-devices marked with V4L2_SUBDEV_FL_HAS_DEVNODE by calling v4l2_device_register_subdev_nodes(). Those device nodes will be automatically removed when sub-devices are unregistered.

The device node handles a subset of the V4L2 API.


The controls ioctls are identical to the ones defined in V4L2. They behave identically, with the only exception that they deal only with controls implemented in the sub-device. Depending on the driver, those controls can be also be accessed through one (or several) V4L2 device nodes.


The events ioctls are identical to the ones defined in V4L2. They behave identically, with the only exception that they deal only with events generated by the sub-device. Depending on the driver, those events can also be reported by one (or several) V4L2 device nodes.

Sub-device drivers that want to use events need to set the V4L2_SUBDEV_USES_EVENTS v4l2_subdev.flags and initialize v4l2_subdev.nevents to events queue depth before registering the sub-device. After registration events can be queued as usual on the v4l2_subdev.devnode device node.

To properly support events, the poll() file operation is also implemented.

Private ioctls

All ioctls not in the above list are passed directly to the sub-device driver through the core::ioctl operation.

1.9. I2C sub-device drivers

Since these drivers are so common, special helper functions are available to ease the use of these drivers (v4l2-common.h).

The recommended method of adding v4l2_subdev support to an I2C driver is to embed the v4l2_subdev struct into the state struct that is created for each I2C device instance. Very simple devices have no state struct and in that case you can just create a v4l2_subdev directly.

A typical state struct would look like this (where ‘chipname’ is replaced by the name of the chip):

struct chipname_state {
        struct v4l2_subdev sd;
        ...  /* additional state fields */

Initialize the v4l2_subdev struct as follows:

v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);

This function will fill in all the fields of v4l2_subdev ensure that the v4l2_subdev and i2c_client both point to one another.

You should also add a helper inline function to go from a v4l2_subdev pointer to a chipname_state struct:

static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
        return container_of(sd, struct chipname_state, sd);

Use this to go from the v4l2_subdev struct to the i2c_client struct:

struct i2c_client *client = v4l2_get_subdevdata(sd);

And this to go from an i2c_client to a v4l2_subdev struct:

struct v4l2_subdev *sd = i2c_get_clientdata(client);

Make sure to call v4l2_device_unregister_subdev()(sd) when the remove() callback is called. This will unregister the sub-device from the bridge driver. It is safe to call this even if the sub-device was never registered.

You need to do this because when the bridge driver destroys the i2c adapter the remove() callbacks are called of the i2c devices on that adapter. After that the corresponding v4l2_subdev structures are invalid, so they have to be unregistered first. Calling v4l2_device_unregister_subdev()(sd) from the remove() callback ensures that this is always done correctly.

The bridge driver also has some helper functions it can use:

struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
                                "module_foo", "chipid", 0x36, NULL);

This loads the given module (can be NULL if no module needs to be loaded) and calls i2c_new_device() with the given i2c_adapter and chip/address arguments. If all goes well, then it registers the subdev with the v4l2_device.

You can also use the last argument of v4l2_i2c_new_subdev() to pass an array of possible I2C addresses that it should probe. These probe addresses are only used if the previous argument is 0. A non-zero argument means that you know the exact i2c address so in that case no probing will take place.

Both functions return NULL if something went wrong.

Note that the chipid you pass to v4l2_i2c_new_subdev() is usually the same as the module name. It allows you to specify a chip variant, e.g. “saa7114” or “saa7115”. In general though the i2c driver autodetects this. The use of chipid is something that needs to be looked at more closely at a later date. It differs between i2c drivers and as such can be confusing. To see which chip variants are supported you can look in the i2c driver code for the i2c_device_id table. This lists all the possibilities.

There are one more helper function:

v4l2_i2c_new_subdev_board() uses an i2c_board_info struct which is passed to the i2c driver and replaces the irq, platform_data and addr arguments.

If the subdev supports the s_config core ops, then that op is called with the irq and platform_data arguments after the subdev was setup.

The v4l2_i2c_new_subdev() function will call v4l2_i2c_new_subdev_board(), internally filling a i2c_board_info structure using the client_type and the addr to fill it.

1.10. V4L2 sub-device functions and data structures

struct v4l2_decode_vbi_line

used to decode_vbi_line


struct v4l2_decode_vbi_line {
  u32 is_second_field;
  u8 * p;
  u32 line;
  u32 type;


Set to 0 for the first (odd) field; set to 1 for the second (even) field.
Pointer to the sliced VBI data from the decoder. On exit, points to the start of the payload.
Line number of the sliced VBI data (1-23)
VBI service type (V4L2_SLICED_*). 0 if no service found
struct v4l2_subdev_io_pin_config

Subdevice external IO pin configuration


struct v4l2_subdev_io_pin_config {
  u32 flags;
  u8 pin;
  u8 function;
  u8 value;
  u8 strength;


bitmask with flags for this pin’s config: V4L2_SUBDEV_IO_PIN_DISABLE - disables a pin config, V4L2_SUBDEV_IO_PIN_OUTPUT - if pin is an output, V4L2_SUBDEV_IO_PIN_INPUT - if pin is an input, V4L2_SUBDEV_IO_PIN_SET_VALUE - to set the output value via value and V4L2_SUBDEV_IO_PIN_ACTIVE_LOW - if active is 0.
Chip external IO pin to configure
Internal signal pad/function to route to IO pin
Initial value for pin - e.g. GPIO output value
Pin drive strength
struct v4l2_subdev_core_ops

Define core ops callbacks for subdevs


struct v4l2_subdev_core_ops {
  int (* log_status) (struct v4l2_subdev *sd);
  int (* s_io_pin_config) (struct v4l2_subdev *sd, size_t n,struct v4l2_subdev_io_pin_config *pincfg);
  int (* init) (struct v4l2_subdev *sd, u32 val);
  int (* load_fw) (struct v4l2_subdev *sd);
  int (* reset) (struct v4l2_subdev *sd, u32 val);
  int (* s_gpio) (struct v4l2_subdev *sd, u32 val);
  long (* ioctl) (struct v4l2_subdev *sd, unsigned int cmd, void *arg);
  long (* compat_ioctl32) (struct v4l2_subdev *sd, unsigned int cmd,unsigned long arg);
  int (* g_register) (struct v4l2_subdev *sd, struct v4l2_dbg_register *reg);
  int (* s_register) (struct v4l2_subdev *sd, const struct v4l2_dbg_register *reg);
  int (* s_power) (struct v4l2_subdev *sd, int on);
  int (* interrupt_service_routine) (struct v4l2_subdev *sd,u32 status, bool *handled);
  int (* subscribe_event) (struct v4l2_subdev *sd, struct v4l2_fh *fh,struct v4l2_event_subscription *sub);
  int (* unsubscribe_event) (struct v4l2_subdev *sd, struct v4l2_fh *fh,struct v4l2_event_subscription *sub);


callback for VIDIOC_LOG_STATUS ioctl handler code.
configure one or more chip I/O pins for chips that multiplex different internal signal pads out to IO pins. This function takes a pointer to an array of ‘n’ pin configuration entries, one for each pin being configured. This function could be called at times other than just subdevice initialization.
initialize the sensor registers to some sort of reasonable default values. Do not use for new drivers and should be removed in existing drivers.
load firmware.
generic reset command. The argument selects which subsystems to reset. Passing 0 will always reset the whole chip. Do not use for new drivers without discussing this first on the linux-media mailinglist. There should be no reason normally to reset a device.
set GPIO pins. Very simple right now, might need to be extended with a direction argument if needed.
called at the end of ioctl() syscall handler at the V4L2 core. used to provide support for private ioctls used on the driver.
called when a 32 bits application uses a 64 bits Kernel, in order to fix data passed from/to userspace.
callback for VIDIOC_G_REGISTER ioctl handler code.
callback for VIDIOC_G_REGISTER ioctl handler code.
puts subdevice in power saving mode (on == 0) or normal operation mode (on == 1).
Called by the bridge chip’s interrupt service handler, when an interrupt status has be raised due to this subdev, so that this subdev can handle the details. It may schedule work to be performed later. It must not sleep. Called from an IRQ context.
used by the drivers to request the control framework that for it to be warned when the value of a control changes.
remove event subscription from the control framework.
struct v4l2_subdev_tuner_ops

Callbacks used when v4l device was opened in radio mode.


struct v4l2_subdev_tuner_ops {
  int (* s_radio) (struct v4l2_subdev *sd);
  int (* s_frequency) (struct v4l2_subdev *sd, const struct v4l2_frequency *freq);
  int (* g_frequency) (struct v4l2_subdev *sd, struct v4l2_frequency *freq);
  int (* enum_freq_bands) (struct v4l2_subdev *sd, struct v4l2_frequency_band *band);
  int (* g_tuner) (struct v4l2_subdev *sd, struct v4l2_tuner *vt);
  int (* s_tuner) (struct v4l2_subdev *sd, const struct v4l2_tuner *vt);
  int (* g_modulator) (struct v4l2_subdev *sd, struct v4l2_modulator *vm);
  int (* s_modulator) (struct v4l2_subdev *sd, const struct v4l2_modulator *vm);
  int (* s_type_addr) (struct v4l2_subdev *sd, struct tuner_setup *type);
  int (* s_config) (struct v4l2_subdev *sd, const struct v4l2_priv_tun_config *config);


callback for VIDIOC_S_RADIO ioctl handler code.
callback for VIDIOC_S_FREQUENCY ioctl handler code.
callback for VIDIOC_G_FREQUENCY ioctl handler code. freq->type must be filled in. Normally done by video_ioctl2() or the bridge driver.
callback for VIDIOC_ENUM_FREQ_BANDS ioctl handler code.
callback for VIDIOC_G_TUNER ioctl handler code.
callback for VIDIOC_S_TUNER ioctl handler code. vt->type must be filled in. Normally done by video_ioctl2 or the bridge driver.
callback for VIDIOC_G_MODULATOR ioctl handler code.
callback for VIDIOC_S_MODULATOR ioctl handler code.
sets tuner type and its I2C addr.
sets tda9887 specific stuff, like port1, port2 and qss
struct v4l2_subdev_audio_ops

Callbacks used for audio-related settings


struct v4l2_subdev_audio_ops {
  int (* s_clock_freq) (struct v4l2_subdev *sd, u32 freq);
  int (* s_i2s_clock_freq) (struct v4l2_subdev *sd, u32 freq);
  int (* s_routing) (struct v4l2_subdev *sd, u32 input, u32 output, u32 config);
  int (* s_stream) (struct v4l2_subdev *sd, int enable);


set the frequency (in Hz) of the audio clock output. Used to slave an audio processor to the video decoder, ensuring that audio and video remain synchronized. Usual values for the frequency are 48000, 44100 or 32000 Hz. If the frequency is not supported, then -EINVAL is returned.
sets I2S speed in bps. This is used to provide a standard way to select I2S clock used by driving digital audio streams at some board designs. Usual values for the frequency are 1024000 and 2048000. If the frequency is not supported, then -EINVAL is returned.
used to define the input and/or output pins of an audio chip, and any additional configuration data. Never attempt to use user-level input IDs (e.g. Composite, S-Video, Tuner) at this level. An i2c device shouldn’t know about whether an input pin is connected to a Composite connector, become on another board or platform it might be connected to something else entirely. The calling driver is responsible for mapping a user-level input to the right pins on the i2c device.
used to notify the audio code that stream will start or has stopped.
struct v4l2_mbus_frame_desc_entry

media bus frame description structure


struct v4l2_mbus_frame_desc_entry {
  u16 flags;
  u32 pixelcode;
  u32 length;


media bus pixel code, valid if FRAME_DESC_FL_BLOB is not set
number of octets per frame, valid if V4L2_MBUS_FRAME_DESC_FL_BLOB is set
struct v4l2_mbus_frame_desc

media bus data frame description


struct v4l2_mbus_frame_desc {
  struct v4l2_mbus_frame_desc_entry entry;
  unsigned short num_entries;


frame descriptors array
number of entries in entry array
struct v4l2_subdev_video_ops

Callbacks used when v4l device was opened in video mode.


struct v4l2_subdev_video_ops {
  int (* s_routing) (struct v4l2_subdev *sd, u32 input, u32 output, u32 config);
  int (* s_crystal_freq) (struct v4l2_subdev *sd, u32 freq, u32 flags);
  int (* g_std) (struct v4l2_subdev *sd, v4l2_std_id *norm);
  int (* s_std) (struct v4l2_subdev *sd, v4l2_std_id norm);
  int (* s_std_output) (struct v4l2_subdev *sd, v4l2_std_id std);
  int (* g_std_output) (struct v4l2_subdev *sd, v4l2_std_id *std);
  int (* querystd) (struct v4l2_subdev *sd, v4l2_std_id *std);
  int (* g_tvnorms) (struct v4l2_subdev *sd, v4l2_std_id *std);
  int (* g_tvnorms_output) (struct v4l2_subdev *sd, v4l2_std_id *std);
  int (* g_input_status) (struct v4l2_subdev *sd, u32 *status);
  int (* s_stream) (struct v4l2_subdev *sd, int enable);
  int (* g_pixelaspect) (struct v4l2_subdev *sd, struct v4l2_fract *aspect);
  int (* g_parm) (struct v4l2_subdev *sd, struct v4l2_streamparm *param);
  int (* s_parm) (struct v4l2_subdev *sd, struct v4l2_streamparm *param);
  int (* g_frame_interval) (struct v4l2_subdev *sd,struct v4l2_subdev_frame_interval *interval);
  int (* s_frame_interval) (struct v4l2_subdev *sd,struct v4l2_subdev_frame_interval *interval);
  int (* s_dv_timings) (struct v4l2_subdev *sd,struct v4l2_dv_timings *timings);
  int (* g_dv_timings) (struct v4l2_subdev *sd,struct v4l2_dv_timings *timings);
  int (* query_dv_timings) (struct v4l2_subdev *sd,struct v4l2_dv_timings *timings);
  int (* g_mbus_config) (struct v4l2_subdev *sd,struct v4l2_mbus_config *cfg);
  int (* s_mbus_config) (struct v4l2_subdev *sd,const struct v4l2_mbus_config *cfg);
  int (* s_rx_buffer) (struct v4l2_subdev *sd, void *buf,unsigned int *size);


see s_routing in audio_ops, except this version is for video devices.
sets the frequency of the crystal used to generate the clocks in Hz. An extra flags field allows device specific configuration regarding clock frequency dividers, etc. If not used, then set flags to 0. If the frequency is not supported, then -EINVAL is returned.
callback for VIDIOC_G_STD ioctl handler code.
callback for VIDIOC_S_STD ioctl handler code.
set v4l2_std_id for video OUTPUT devices. This is ignored by video input devices.
get current standard for video OUTPUT devices. This is ignored by video input devices.
callback for VIDIOC_QUERYSTD ioctl handler code.
get v4l2_std_id with all standards supported by the video CAPTURE device. This is ignored by video output devices.
get v4l2_std_id with all standards supported by the video OUTPUT device. This is ignored by video capture devices.
get input status. Same as the status field in the struct v4l2_input
used to notify the driver that a video stream will start or has stopped.
callback to return the pixelaspect ratio.
callback for VIDIOC_G_PARM ioctl handler code.
callback for VIDIOC_S_PARM ioctl handler code.
callback for VIDIOC_G_FRAMEINTERVAL ioctl handler code.
callback for VIDIOC_S_FRAMEINTERVAL ioctl handler code.
Set custom dv timings in the sub device. This is used when sub device is capable of setting detailed timing information in the hardware to generate/detect the video signal.
Get custom dv timings in the sub device.
callback for VIDIOC_QUERY_DV_TIMINGS ioctl handler code.
get supported mediabus configurations
set a certain mediabus configuration. This operation is added for compatibility with soc-camera drivers and should not be used by new software.
set a host allocated memory buffer for the subdev. The subdev can adjust size to a lower value and must not write more data to the buffer starting at data than the original value of size.
struct v4l2_subdev_vbi_ops

Callbacks used when v4l device was opened in video mode via the vbi device node.


struct v4l2_subdev_vbi_ops {
  int (* decode_vbi_line) (struct v4l2_subdev *sd, struct v4l2_decode_vbi_line *vbi_line);
  int (* s_vbi_data) (struct v4l2_subdev *sd, const struct v4l2_sliced_vbi_data *vbi_data);
  int (* g_vbi_data) (struct v4l2_subdev *sd, struct v4l2_sliced_vbi_data *vbi_data);
  int (* g_sliced_vbi_cap) (struct v4l2_subdev *sd, struct v4l2_sliced_vbi_cap *cap);
  int (* s_raw_fmt) (struct v4l2_subdev *sd, struct v4l2_vbi_format *fmt);
  int (* g_sliced_fmt) (struct v4l2_subdev *sd, struct v4l2_sliced_vbi_format *fmt);
  int (* s_sliced_fmt) (struct v4l2_subdev *sd, struct v4l2_sliced_vbi_format *fmt);


video decoders that support sliced VBI need to implement this ioctl. Field p of the struct v4l2_decode_vbi_line is set to the start of the VBI data that was generated by the decoder. The driver then parses the sliced VBI data and sets the other fields in the struct accordingly. The pointer p is updated to point to the start of the payload which can be copied verbatim into the data field of the struct v4l2_sliced_vbi_data. If no valid VBI data was found, then the type field is set to 0 on return.
used to generate VBI signals on a video signal. struct v4l2_sliced_vbi_data is filled with the data packets that should be output. Note that if you set the line field to 0, then that VBI signal is disabled. If no valid VBI data was found, then the type field is set to 0 on return.
used to obtain the sliced VBI packet from a readback register. Not all video decoders support this. If no data is available because the readback register contains invalid or erroneous data -EIO is returned. Note that you must fill in the ‘id’ member and the ‘field’ member (to determine whether CC data from the first or second field should be obtained).
callback for VIDIOC_SLICED_VBI_CAP ioctl handler code.
setup the video encoder/decoder for raw VBI.
retrieve the current sliced VBI settings.
setup the sliced VBI settings.
struct v4l2_subdev_sensor_ops

v4l2-subdev sensor operations


struct v4l2_subdev_sensor_ops {
  int (* g_skip_top_lines) (struct v4l2_subdev *sd, u32 *lines);
  int (* g_skip_frames) (struct v4l2_subdev *sd, u32 *frames);


number of lines at the top of the image to be skipped. This is needed for some sensors, which always corrupt several top lines of the output image, or which send their metadata in them.
number of frames to skip at stream start. This is needed for buggy sensors that generate faulty frames when they are turned on.
enum v4l2_subdev_ir_mode

describes the type of IR supported


IR uses struct ir_raw_event records
struct v4l2_subdev_ir_parameters

Parameters for IR TX or TX


struct v4l2_subdev_ir_parameters {
  unsigned int bytes_per_data_element;
  enum v4l2_subdev_ir_mode mode;
  bool enable;
  bool interrupt_enable;
  bool shutdown;
  bool modulation;
  u32 max_pulse_width;
  unsigned int carrier_freq;
  unsigned int duty_cycle;
  bool invert_level;
  bool invert_carrier_sense;
  u32 noise_filter_min_width;
  unsigned int carrier_range_lower;
  unsigned int carrier_range_upper;
  u32 resolution;


bytes per data element of data in read or write call.
IR mode as defined by enum v4l2_subdev_ir_mode.
device is active if true
IR interrupts are enabled if true
if true: set hardware to low/no power, false: normal mode
if true, it uses carrier, if false: baseband
maximum pulse width in ns, valid only for baseband signal
carrier frequency in Hz, valid only for modulated signal
duty cycle percentage, valid only for modulated signal
invert signal level
Send 0/space as a carrier burst. used only in TX.
min time of a valid pulse, in ns. Used only for RX.
Lower carrier range, in Hz, valid only for modulated signal. Used only for RX.
Upper carrier range, in Hz, valid only for modulated signal. Used only for RX.
The receive resolution, in ns . Used only for RX.
struct v4l2_subdev_ir_ops

operations for IR subdevices


struct v4l2_subdev_ir_ops {
  int (* rx_read) (struct v4l2_subdev *sd, u8 *buf, size_t count,ssize_t *num);
  int (* rx_g_parameters) (struct v4l2_subdev *sd,struct v4l2_subdev_ir_parameters *params);
  int (* rx_s_parameters) (struct v4l2_subdev *sd,struct v4l2_subdev_ir_parameters *params);
  int (* tx_write) (struct v4l2_subdev *sd, u8 *buf, size_t count,ssize_t *num);
  int (* tx_g_parameters) (struct v4l2_subdev *sd,struct v4l2_subdev_ir_parameters *params);
  int (* tx_s_parameters) (struct v4l2_subdev *sd,struct v4l2_subdev_ir_parameters *params);


Reads received codes or pulse width data. The semantics are similar to a non-blocking read() call.
Get the current operating parameters and state of the the IR receiver.
Set the current operating parameters and state of the the IR receiver. It is recommended to call [rt]x_g_parameters first to fill out the current state, and only change the fields that need to be changed. Upon return, the actual device operating parameters and state will be returned. Note that hardware limitations may prevent the actual settings from matching the requested settings - e.g. an actual carrier setting of 35,904 Hz when 36,000 Hz was requested. An exception is when the shutdown parameter is true. The last used operational parameters will be returned, but the actual state of the hardware be different to minimize power consumption and processing when shutdown is true.
Writes codes or pulse width data for transmission. The semantics are similar to a non-blocking write() call.
Get the current operating parameters and state of the the IR transmitter.
Set the current operating parameters and state of the the IR transmitter. It is recommended to call [rt]x_g_parameters first to fill out the current state, and only change the fields that need to be changed. Upon return, the actual device operating parameters and state will be returned. Note that hardware limitations may prevent the actual settings from matching the requested settings - e.g. an actual carrier setting of 35,904 Hz when 36,000 Hz was requested. An exception is when the shutdown parameter is true. The last used operational parameters will be returned, but the actual state of the hardware be different to minimize power consumption and processing when shutdown is true.
struct v4l2_subdev_pad_config

Used for storing subdev pad information.


struct v4l2_subdev_pad_config {
  struct v4l2_mbus_framefmt try_fmt;
  struct v4l2_rect try_crop;
  struct v4l2_rect try_compose;


struct v4l2_mbus_framefmt
struct v4l2_rect to be used for crop
struct v4l2_rect to be used for compose


This structure only needs to be passed to the pad op if the ‘which’ field of the main argument is set to V4L2_SUBDEV_FORMAT_TRY. For V4L2_SUBDEV_FORMAT_ACTIVE it is safe to pass NULL.

struct v4l2_subdev_pad_ops

v4l2-subdev pad level operations


struct v4l2_subdev_pad_ops {
  int (* init_cfg) (struct v4l2_subdev *sd,struct v4l2_subdev_pad_config *cfg);
  int (* enum_mbus_code) (struct v4l2_subdev *sd,struct v4l2_subdev_pad_config *cfg,struct v4l2_subdev_mbus_code_enum *code);
  int (* enum_frame_size) (struct v4l2_subdev *sd,struct v4l2_subdev_pad_config *cfg,struct v4l2_subdev_frame_size_enum *fse);
  int (* enum_frame_interval) (struct v4l2_subdev *sd,struct v4l2_subdev_pad_config *cfg,struct v4l2_subdev_frame_interval_enum *fie);
  int (* get_fmt) (struct v4l2_subdev *sd,struct v4l2_subdev_pad_config *cfg,struct v4l2_subdev_format *format);
  int (* set_fmt) (struct v4l2_subdev *sd,struct v4l2_subdev_pad_config *cfg,struct v4l2_subdev_format *format);
  int (* get_selection) (struct v4l2_subdev *sd,struct v4l2_subdev_pad_config *cfg,struct v4l2_subdev_selection *sel);
  int (* set_selection) (struct v4l2_subdev *sd,struct v4l2_subdev_pad_config *cfg,struct v4l2_subdev_selection *sel);
  int (* get_edid) (struct v4l2_subdev *sd, struct v4l2_edid *edid);
  int (* set_edid) (struct v4l2_subdev *sd, struct v4l2_edid *edid);
  int (* dv_timings_cap) (struct v4l2_subdev *sd,struct v4l2_dv_timings_cap *cap);
  int (* enum_dv_timings) (struct v4l2_subdev *sd,struct v4l2_enum_dv_timings *timings);
  int (* link_validate) (struct v4l2_subdev *sd, struct media_link *link,struct v4l2_subdev_format *source_fmt,struct v4l2_subdev_format *sink_fmt);
  int (* get_frame_desc) (struct v4l2_subdev *sd, unsigned int pad,struct v4l2_mbus_frame_desc *fd);
  int (* set_frame_desc) (struct v4l2_subdev *sd, unsigned int pad,struct v4l2_mbus_frame_desc *fd);


initialize the pad config to default values
callback for VIDIOC_SUBDEV_ENUM_MBUS_CODE ioctl handler code.
callback for VIDIOC_SUBDEV_ENUM_FRAME_SIZE ioctl handler code.
callback for VIDIOC_SUBDEV_ENUM_FRAME_INTERVAL ioctl handler code.
callback for VIDIOC_SUBDEV_G_FMT ioctl handler code.
callback for VIDIOC_SUBDEV_S_FMT ioctl handler code.
callback for VIDIOC_SUBDEV_G_SELECTION ioctl handler code.
callback for VIDIOC_SUBDEV_S_SELECTION ioctl handler code.
callback for VIDIOC_SUBDEV_G_EDID ioctl handler code.
callback for VIDIOC_SUBDEV_S_EDID ioctl handler code.
callback for VIDIOC_SUBDEV_DV_TIMINGS_CAP ioctl handler code.
callback for VIDIOC_SUBDEV_ENUM_DV_TIMINGS ioctl handler code.
used by the media controller code to check if the links that belongs to a pipeline can be used for stream.
get the current low level media bus frame parameters.
set the low level media bus frame parameters, fd array may be adjusted by the subdev driver to device capabilities.
struct v4l2_subdev_ops

Subdev operations


struct v4l2_subdev_ops {
  const struct v4l2_subdev_core_ops * core;
  const struct v4l2_subdev_tuner_ops * tuner;
  const struct v4l2_subdev_audio_ops * audio;
  const struct v4l2_subdev_video_ops * video;
  const struct v4l2_subdev_vbi_ops * vbi;
  const struct v4l2_subdev_ir_ops * ir;
  const struct v4l2_subdev_sensor_ops * sensor;
  const struct v4l2_subdev_pad_ops * pad;


pointer to struct v4l2_subdev_core_ops. Can be NULL
pointer to struct v4l2_subdev_tuner_ops. Can be NULL
pointer to struct v4l2_subdev_audio_ops. Can be NULL
pointer to struct v4l2_subdev_video_ops. Can be NULL
pointer to struct v4l2_subdev_vbi_ops. Can be NULL
pointer to struct v4l2_subdev_ir_ops. Can be NULL
pointer to struct v4l2_subdev_sensor_ops. Can be NULL
pointer to struct v4l2_subdev_pad_ops. Can be NULL
struct v4l2_subdev_internal_ops

V4L2 subdev internal ops


struct v4l2_subdev_internal_ops {
  int (* registered) (struct v4l2_subdev *sd);
  void (* unregistered) (struct v4l2_subdev *sd);
  int (* open) (struct v4l2_subdev *sd, struct v4l2_subdev_fh *fh);
  int (* close) (struct v4l2_subdev *sd, struct v4l2_subdev_fh *fh);


called when this subdev is registered. When called the v4l2_dev field is set to the correct v4l2_device.
called when this subdev is unregistered. When called the v4l2_dev field is still set to the correct v4l2_device.
called when the subdev device node is opened by an application.
called when the subdev device node is closed.



Never call this from drivers, only the v4l2 framework can call these ops.

struct v4l2_subdev_platform_data

regulators config struct


struct v4l2_subdev_platform_data {
  struct regulator_bulk_data * regulators;
  int num_regulators;
  void * host_priv;


Optional regulators used to power on/off the subdevice
Number of regululators
Per-subdevice data, specific for a certain video host device
struct v4l2_subdev

describes a V4L2 sub-device


struct v4l2_subdev {
  struct media_entity entity;
  struct list_head list;
  struct module * owner;
  bool owner_v4l2_dev;
  u32 flags;
  struct v4l2_device * v4l2_dev;
  const struct v4l2_subdev_ops * ops;
  const struct v4l2_subdev_internal_ops * internal_ops;
  struct v4l2_ctrl_handler * ctrl_handler;
  char name;
  u32 grp_id;
  void * dev_priv;
  void * host_priv;
  struct video_device * devnode;
  struct device * dev;
  struct device_node * of_node;
  struct list_head async_list;
  struct v4l2_async_subdev * asd;
  struct v4l2_async_notifier * notifier;
  struct v4l2_subdev_platform_data * pdata;


pointer to struct media_entity
List of sub-devices
The owner is the same as the driver’s struct device owner.
true if the sd->owner matches the owner of v4l2_dev->dev ownner. Initialized by v4l2_device_register_subdev().
subdev flags. Can be: V4L2_SUBDEV_FL_IS_I2C - Set this flag if this subdev is a i2c device; V4L2_SUBDEV_FL_IS_SPI - Set this flag if this subdev is a spi device; V4L2_SUBDEV_FL_HAS_DEVNODE - Set this flag if this subdev needs a device node; V4L2_SUBDEV_FL_HAS_EVENTS - Set this flag if this subdev generates events.
pointer to struct v4l2_device
pointer to struct v4l2_subdev_ops
pointer to struct v4l2_subdev_internal_ops. Never call these internal ops from within a driver!
The control handler of this subdev. May be NULL.
Name of the sub-device. Please notice that the name must be unique.
can be used to group similar subdevs. Value is driver-specific
pointer to private data
pointer to private data used by the device where the subdev is attached.
subdev device node
pointer to the physical device, if any
The device_node of the subdev, usually the same as dev->of_node.
Links this subdev to a global subdev_list or notifier->done list.
Pointer to respective struct v4l2_async_subdev.
Pointer to the managing notifier.
common part of subdevice platform data


Each instance of a subdev driver should create this struct, either stand-alone or embedded in a larger struct.

This structure should be initialized by v4l2_subdev_init() or one of its variants: v4l2_spi_subdev_init(), v4l2_i2c_subdev_init().

struct v4l2_subdev_fh

Used for storing subdev information per file handle


struct v4l2_subdev_fh {
  struct v4l2_fh vfh;
  struct v4l2_subdev_pad_config * pad;


pointer to struct v4l2_fh
pointer to v4l2_subdev_pad_config
void v4l2_set_subdevdata(struct v4l2_subdev * sd, void * p)

Sets V4L2 dev private device data


struct v4l2_subdev * sd
pointer to struct v4l2_subdev
void * p
pointer to the private device data to be stored.
void * v4l2_get_subdevdata(const struct v4l2_subdev * sd)

Gets V4L2 dev private device data


const struct v4l2_subdev * sd
pointer to struct v4l2_subdev


Returns the pointer to the private device data to be stored.

void v4l2_set_subdev_hostdata(struct v4l2_subdev * sd, void * p)

Sets V4L2 dev private host data


struct v4l2_subdev * sd
pointer to struct v4l2_subdev
void * p
pointer to the private data to be stored.
void * v4l2_get_subdev_hostdata(const struct v4l2_subdev * sd)

Gets V4L2 dev private data


const struct v4l2_subdev * sd
pointer to struct v4l2_subdev


Returns the pointer to the private host data to be stored.

validates a media link


struct v4l2_subdev * sd
pointer to struct v4l2_subdev
struct media_link * link
pointer to struct media_link
struct v4l2_subdev_format * source_fmt
pointer to struct v4l2_subdev_format
struct v4l2_subdev_format * sink_fmt
pointer to struct v4l2_subdev_format


This function ensures that width, height and the media bus pixel code are equal on both source and sink of the link.

validates a media link


struct media_link * link
pointer to struct media_link


This function calls the subdev’s link_validate ops to validate if a media link is valid for streaming. It also internally calls v4l2_subdev_link_validate_default() to ensure that width, height and the media bus pixel code are equal on both source and sink of the link.

struct v4l2_subdev_pad_config * v4l2_subdev_alloc_pad_config(struct v4l2_subdev * sd)

Allocates memory for pad config


struct v4l2_subdev * sd
pointer to struct v4l2_subdev
void v4l2_subdev_free_pad_config(struct v4l2_subdev_pad_config * cfg)

Frees memory allocated by v4l2_subdev_alloc_pad_config().


struct v4l2_subdev_pad_config * cfg
pointer to struct v4l2_subdev_pad_config
void v4l2_subdev_init(struct v4l2_subdev * sd, const struct v4l2_subdev_ops * ops)

initializes the sub-device struct


struct v4l2_subdev * sd
pointer to the struct v4l2_subdev to be initialized
const struct v4l2_subdev_ops * ops
pointer to struct v4l2_subdev_ops.
void v4l2_subdev_notify_event(struct v4l2_subdev * sd, const struct v4l2_event * ev)

Delivers event notification for subdevice


struct v4l2_subdev * sd
The subdev for which to deliver the event
const struct v4l2_event * ev
The event to deliver


Will deliver the specified event to all userspace event listeners which are subscribed to the v42l subdev event queue as well as to the bridge driver using the notify callback. The notification type for the notify callback will be V4L2_DEVICE_NOTIFY_EVENT.

enum v4l2_async_match_type

type of asynchronous subdevice logic to be used in order to identify a match


Match will use the logic provided by struct v4l2_async_subdev.match ops
Match will use the device name
Match will check for I2C adapter ID and address
Match will use OF node


This enum is used by the asyncrhronous sub-device logic to define the algorithm that will be used to match an asynchronous device.

struct v4l2_async_subdev

sub-device descriptor, as known to a bridge


struct v4l2_async_subdev {
  enum v4l2_async_match_type match_type;
  union match;
  struct list_head list;


type of match that will be used
union of per-bus type matching data sets
used to link struct v4l2_async_subdev objects, waiting to be probed, to a notifier->waiting list
struct v4l2_async_notifier

v4l2_device notifier data


struct v4l2_async_notifier {
  unsigned int num_subdevs;
  struct v4l2_async_subdev ** subdevs;
  struct v4l2_device * v4l2_dev;
  struct list_head waiting;
  struct list_head done;
  struct list_head list;
  int (* bound) (struct v4l2_async_notifier *notifier,struct v4l2_subdev *subdev,struct v4l2_async_subdev *asd);
  int (* complete) (struct v4l2_async_notifier *notifier);
  void (* unbind) (struct v4l2_async_notifier *notifier,struct v4l2_subdev *subdev,struct v4l2_async_subdev *asd);


number of subdevices
array of pointers to subdevice descriptors
pointer to struct v4l2_device
list of struct v4l2_async_subdev, waiting for their drivers
list of struct v4l2_subdev, already probed
member in a global list of notifiers
a subdevice driver has successfully probed one of subdevices
all subdevices have been probed successfully
a subdevice is leaving
int v4l2_async_notifier_register(struct v4l2_device * v4l2_dev, struct v4l2_async_notifier * notifier)

registers a subdevice asynchronous notifier


struct v4l2_device * v4l2_dev
pointer to struct v4l2_device
struct v4l2_async_notifier * notifier
pointer to struct v4l2_async_notifier
void v4l2_async_notifier_unregister(struct v4l2_async_notifier * notifier)

unregisters a subdevice asynchronous notifier


struct v4l2_async_notifier * notifier
pointer to struct v4l2_async_notifier
int v4l2_async_register_subdev(struct v4l2_subdev * sd)

registers a sub-device to the asynchronous subdevice framework


struct v4l2_subdev * sd
pointer to struct v4l2_subdev
void v4l2_async_unregister_subdev(struct v4l2_subdev * sd)

unregisters a sub-device to the asynchronous subdevice framework


struct v4l2_subdev * sd
pointer to struct v4l2_subdev