2008-11-29 17:36:58 -07:00
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Overview of the V4L2 driver framework
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=====================================
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This text documents the various structures provided by the V4L2 framework and
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their relationships.
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Introduction
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------------
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The V4L2 drivers tend to be very complex due to the complexity of the
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hardware: most devices have multiple ICs, export multiple device nodes in
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/dev, and create also non-V4L2 devices such as DVB, ALSA, FB, I2C and input
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(IR) devices.
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Especially the fact that V4L2 drivers have to setup supporting ICs to
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do audio/video muxing/encoding/decoding makes it more complex than most.
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Usually these ICs are connected to the main bridge driver through one or
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more I2C busses, but other busses can also be used. Such devices are
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called 'sub-devices'.
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For a long time the framework was limited to the video_device struct for
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creating V4L device nodes and video_buf for handling the video buffers
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(note that this document does not discuss the video_buf framework).
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This meant that all drivers had to do the setup of device instances and
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connecting to sub-devices themselves. Some of this is quite complicated
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to do right and many drivers never did do it correctly.
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There is also a lot of common code that could never be refactored due to
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the lack of a framework.
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So this framework sets up the basic building blocks that all drivers
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need and this same framework should make it much easier to refactor
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common code into utility functions shared by all drivers.
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Structure of a driver
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---------------------
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All drivers have the following structure:
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1) A struct for each device instance containing the device state.
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2) A way of initializing and commanding sub-devices (if any).
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3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX, /dev/radioX and
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/dev/vtxX) and keeping track of device-node specific data.
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2009-02-14 03:29:07 -07:00
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4) Filehandle-specific structs containing per-filehandle data;
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5) video buffer handling.
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2008-11-29 17:36:58 -07:00
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This is a rough schematic of how it all relates:
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device instances
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+-sub-device instances
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\-V4L2 device nodes
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\-filehandle instances
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Structure of the framework
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--------------------------
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The framework closely resembles the driver structure: it has a v4l2_device
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struct for the device instance data, a v4l2_subdev struct to refer to
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sub-device instances, the video_device struct stores V4L2 device node data
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and in the future a v4l2_fh struct will keep track of filehandle instances
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(this is not yet implemented).
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struct v4l2_device
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------------------
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Each device instance is represented by a struct v4l2_device (v4l2-device.h).
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Very simple devices can just allocate this struct, but most of the time you
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would embed this struct inside a larger struct.
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You must register the device instance:
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v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev);
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Registration will initialize the v4l2_device struct and link dev->driver_data
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2009-02-14 07:54:23 -07:00
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to v4l2_dev. If v4l2_dev->name is empty then it will be set to a value derived
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from dev (driver name followed by the bus_id, to be precise). If you set it
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up before calling v4l2_device_register then it will be untouched. If dev is
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NULL, then you *must* setup v4l2_dev->name before calling v4l2_device_register.
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2008-11-29 17:36:58 -07:00
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2009-05-02 07:12:50 -06:00
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You can use v4l2_device_set_name() to set the name based on a driver name and
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a driver-global atomic_t instance. This will generate names like ivtv0, ivtv1,
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etc. If the name ends with a digit, then it will insert a dash: cx18-0,
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cx18-1, etc. This function returns the instance number.
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2008-12-19 06:20:22 -07:00
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The first 'dev' argument is normally the struct device pointer of a pci_dev,
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2009-04-01 05:30:06 -06:00
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usb_interface or platform_device. It is rare for dev to be NULL, but it happens
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2009-03-13 07:03:04 -06:00
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with ISA devices or when one device creates multiple PCI devices, thus making
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it impossible to associate v4l2_dev with a particular parent.
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2008-12-19 06:20:22 -07:00
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2009-03-08 14:02:10 -06:00
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You can also supply a notify() callback that can be called by sub-devices to
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notify you of events. Whether you need to set this depends on the sub-device.
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Any notifications a sub-device supports must be defined in a header in
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include/media/<subdevice>.h.
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2008-11-29 17:36:58 -07:00
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You unregister with:
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v4l2_device_unregister(struct v4l2_device *v4l2_dev);
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Unregistering will also automatically unregister all subdevs from the device.
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2009-03-14 05:28:45 -06:00
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If you have a hotpluggable device (e.g. a USB device), then when a disconnect
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happens the parent device becomes invalid. Since v4l2_device has a pointer to
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that parent device it has to be cleared as well to mark that the parent is
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gone. To do this call:
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v4l2_device_disconnect(struct v4l2_device *v4l2_dev);
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This does *not* unregister the subdevs, so you still need to call the
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v4l2_device_unregister() function for that. If your driver is not hotpluggable,
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then there is no need to call v4l2_device_disconnect().
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2008-11-29 17:36:58 -07:00
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Sometimes you need to iterate over all devices registered by a specific
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driver. This is usually the case if multiple device drivers use the same
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hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv
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hardware. The same is true for alsa drivers for example.
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You can iterate over all registered devices as follows:
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static int callback(struct device *dev, void *p)
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{
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struct v4l2_device *v4l2_dev = dev_get_drvdata(dev);
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/* test if this device was inited */
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if (v4l2_dev == NULL)
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return 0;
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...
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return 0;
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}
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int iterate(void *p)
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{
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struct device_driver *drv;
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int err;
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/* Find driver 'ivtv' on the PCI bus.
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pci_bus_type is a global. For USB busses use usb_bus_type. */
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drv = driver_find("ivtv", &pci_bus_type);
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/* iterate over all ivtv device instances */
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err = driver_for_each_device(drv, NULL, p, callback);
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put_driver(drv);
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return err;
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}
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Sometimes you need to keep a running counter of the device instance. This is
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commonly used to map a device instance to an index of a module option array.
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The recommended approach is as follows:
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static atomic_t drv_instance = ATOMIC_INIT(0);
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2009-02-07 03:07:04 -07:00
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static int __devinit drv_probe(struct pci_dev *pdev,
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2008-11-29 17:36:58 -07:00
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const struct pci_device_id *pci_id)
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{
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...
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state->instance = atomic_inc_return(&drv_instance) - 1;
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}
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struct v4l2_subdev
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------------------
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Many drivers need to communicate with sub-devices. These devices can do all
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sort of tasks, but most commonly they handle audio and/or video muxing,
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encoding or decoding. For webcams common sub-devices are sensors and camera
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controllers.
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Usually these are I2C devices, but not necessarily. In order to provide the
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driver with a consistent interface to these sub-devices the v4l2_subdev struct
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(v4l2-subdev.h) was created.
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Each sub-device driver must have a v4l2_subdev struct. This struct can be
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stand-alone for simple sub-devices or it might be embedded in a larger struct
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if more state information needs to be stored. Usually there is a low-level
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device struct (e.g. i2c_client) that contains the device data as setup
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by the kernel. It is recommended to store that pointer in the private
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data of v4l2_subdev using v4l2_set_subdevdata(). That makes it easy to go
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from a v4l2_subdev to the actual low-level bus-specific device data.
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You also need a way to go from the low-level struct to v4l2_subdev. For the
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common i2c_client struct the i2c_set_clientdata() call is used to store a
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v4l2_subdev pointer, for other busses you may have to use other methods.
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From the bridge driver perspective you load the sub-device module and somehow
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obtain the v4l2_subdev pointer. For i2c devices this is easy: you call
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i2c_get_clientdata(). For other busses something similar needs to be done.
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Helper functions exists for sub-devices on an I2C bus that do most of this
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tricky work for you.
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Each v4l2_subdev contains function pointers that sub-device drivers can
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implement (or leave NULL if it is not applicable). Since sub-devices can do
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so many different things and you do not want to end up with a huge ops struct
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of which only a handful of ops are commonly implemented, the function pointers
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are sorted according to category and each category has its own ops struct.
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The top-level ops struct contains pointers to the category ops structs, which
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may be NULL if the subdev driver does not support anything from that category.
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It looks like this:
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struct v4l2_subdev_core_ops {
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2008-12-30 03:14:19 -07:00
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int (*g_chip_ident)(struct v4l2_subdev *sd, struct v4l2_dbg_chip_ident *chip);
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2008-11-29 17:36:58 -07:00
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int (*log_status)(struct v4l2_subdev *sd);
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int (*init)(struct v4l2_subdev *sd, u32 val);
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...
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};
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struct v4l2_subdev_tuner_ops {
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...
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};
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struct v4l2_subdev_audio_ops {
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...
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};
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struct v4l2_subdev_video_ops {
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...
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};
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struct v4l2_subdev_ops {
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const struct v4l2_subdev_core_ops *core;
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const struct v4l2_subdev_tuner_ops *tuner;
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const struct v4l2_subdev_audio_ops *audio;
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const struct v4l2_subdev_video_ops *video;
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};
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The core ops are common to all subdevs, the other categories are implemented
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depending on the sub-device. E.g. a video device is unlikely to support the
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audio ops and vice versa.
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This setup limits the number of function pointers while still making it easy
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to add new ops and categories.
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A sub-device driver initializes the v4l2_subdev struct using:
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2009-02-07 03:07:04 -07:00
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v4l2_subdev_init(sd, &ops);
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Afterwards you need to initialize subdev->name with a unique name and set the
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module owner. This is done for you if you use the i2c helper functions.
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A device (bridge) driver needs to register the v4l2_subdev with the
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v4l2_device:
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2009-02-07 03:07:04 -07:00
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int err = v4l2_device_register_subdev(v4l2_dev, sd);
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This can fail if the subdev module disappeared before it could be registered.
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After this function was called successfully the subdev->dev field points to
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the v4l2_device.
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You can unregister a sub-device using:
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2009-02-07 03:07:04 -07:00
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v4l2_device_unregister_subdev(sd);
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2008-11-29 17:36:58 -07:00
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2009-02-07 03:07:04 -07:00
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Afterwards the subdev module can be unloaded and sd->dev == NULL.
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2008-11-29 17:36:58 -07:00
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You can call an ops function either directly:
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2009-02-07 03:07:04 -07:00
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err = sd->ops->core->g_chip_ident(sd, &chip);
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2008-11-29 17:36:58 -07:00
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but it is better and easier to use this macro:
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2009-02-07 03:07:04 -07:00
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err = v4l2_subdev_call(sd, core, g_chip_ident, &chip);
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The macro will to the right NULL pointer checks and returns -ENODEV if subdev
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is NULL, -ENOIOCTLCMD if either subdev->core or subdev->core->g_chip_ident is
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NULL, or the actual result of the subdev->ops->core->g_chip_ident ops.
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It is also possible to call all or a subset of the sub-devices:
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2009-02-07 03:07:04 -07:00
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v4l2_device_call_all(v4l2_dev, 0, core, g_chip_ident, &chip);
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Any subdev that does not support this ops is skipped and error results are
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ignored. If you want to check for errors use this:
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2009-02-07 03:07:04 -07:00
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err = v4l2_device_call_until_err(v4l2_dev, 0, core, g_chip_ident, &chip);
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Any error except -ENOIOCTLCMD will exit the loop with that error. If no
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errors (except -ENOIOCTLCMD) occured, then 0 is returned.
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The second argument to both calls is a group ID. If 0, then all subdevs are
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called. If non-zero, then only those whose group ID match that value will
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be called. Before a bridge driver registers a subdev it can set sd->grp_id
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to whatever value it wants (it's 0 by default). This value is owned by the
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bridge driver and the sub-device driver will never modify or use it.
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The group ID gives the bridge driver more control how callbacks are called.
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For example, there may be multiple audio chips on a board, each capable of
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changing the volume. But usually only one will actually be used when the
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user want to change the volume. You can set the group ID for that subdev to
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e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling
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v4l2_device_call_all(). That ensures that it will only go to the subdev
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that needs it.
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2009-03-08 14:02:10 -06:00
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If the sub-device needs to notify its v4l2_device parent of an event, then
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it can call v4l2_subdev_notify(sd, notification, arg). This macro checks
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whether there is a notify() callback defined and returns -ENODEV if not.
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Otherwise the result of the notify() call is returned.
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2008-11-29 17:36:58 -07:00
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The advantage of using v4l2_subdev is that it is a generic struct and does
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not contain any knowledge about the underlying hardware. So a driver might
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contain several subdevs that use an I2C bus, but also a subdev that is
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controlled through GPIO pins. This distinction is only relevant when setting
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up the device, but once the subdev is registered it is completely transparent.
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I2C sub-device drivers
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----------------------
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Since these drivers are so common, special helper functions are available to
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ease the use of these drivers (v4l2-common.h).
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The recommended method of adding v4l2_subdev support to an I2C driver is to
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embed the v4l2_subdev struct into the state struct that is created for each
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I2C device instance. Very simple devices have no state struct and in that case
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|
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 and 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.
|
|
|
|
|
2009-01-15 02:09:05 -07:00
|
|
|
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.
|
|
|
|
|
2008-11-29 17:36:58 -07:00
|
|
|
|
|
|
|
The bridge driver also has some helper functions it can use:
|
|
|
|
|
2009-04-01 00:57:53 -06:00
|
|
|
struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
|
2009-08-09 23:49:08 -06:00
|
|
|
"module_foo", "chipid", 0x36, NULL);
|
2008-11-29 17:36:58 -07:00
|
|
|
|
|
|
|
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.
|
2009-04-01 00:57:53 -06:00
|
|
|
If all goes well, then it registers the subdev with the v4l2_device.
|
2008-11-29 17:36:58 -07:00
|
|
|
|
2009-08-09 23:49:08 -06:00
|
|
|
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.
|
2008-11-29 17:36:58 -07:00
|
|
|
|
|
|
|
Both functions return NULL if something went wrong.
|
|
|
|
|
2009-08-09 23:49:08 -06:00
|
|
|
Note that the chipid you pass to v4l2_i2c_new_subdev() is usually
|
2009-03-12 15:34:19 -06:00
|
|
|
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.
|
|
|
|
|
2009-06-09 14:29:29 -06:00
|
|
|
There are two more helper functions:
|
|
|
|
|
|
|
|
v4l2_i2c_new_subdev_cfg: this function adds new irq and platform_data
|
|
|
|
arguments and has both 'addr' and 'probed_addrs' arguments: if addr is not
|
|
|
|
0 then that will be used (non-probing variant), otherwise the probed_addrs
|
|
|
|
are probed.
|
|
|
|
|
|
|
|
For example: this will probe for address 0x10:
|
|
|
|
|
|
|
|
struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter,
|
|
|
|
"module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10));
|
|
|
|
|
|
|
|
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 older
|
|
|
|
v4l2_i2c_new_(probed_)subdev functions will call s_config as well, but with
|
|
|
|
irq set to 0 and platform_data set to NULL.
|
|
|
|
|
2008-11-29 17:36:58 -07:00
|
|
|
struct video_device
|
|
|
|
-------------------
|
|
|
|
|
2008-12-19 06:20:22 -07:00
|
|
|
The actual device nodes in the /dev directory are created using the
|
|
|
|
video_device struct (v4l2-dev.h). This struct can either be allocated
|
|
|
|
dynamically or embedded in a larger struct.
|
|
|
|
|
|
|
|
To allocate it dynamically use:
|
|
|
|
|
|
|
|
struct video_device *vdev = video_device_alloc();
|
|
|
|
|
|
|
|
if (vdev == NULL)
|
|
|
|
return -ENOMEM;
|
|
|
|
|
|
|
|
vdev->release = video_device_release;
|
|
|
|
|
|
|
|
If you embed it in a larger struct, then you must set the release()
|
|
|
|
callback to your own function:
|
|
|
|
|
|
|
|
struct video_device *vdev = &my_vdev->vdev;
|
|
|
|
|
|
|
|
vdev->release = my_vdev_release;
|
|
|
|
|
|
|
|
The release callback must be set and it is called when the last user
|
|
|
|
of the video device exits.
|
|
|
|
|
|
|
|
The default video_device_release() callback just calls kfree to free the
|
|
|
|
allocated memory.
|
|
|
|
|
|
|
|
You should also set these fields:
|
|
|
|
|
2008-12-23 08:17:23 -07:00
|
|
|
- v4l2_dev: set to the v4l2_device parent device.
|
2008-12-19 06:20:22 -07:00
|
|
|
- name: set to something descriptive and unique.
|
2008-12-23 09:42:25 -07:00
|
|
|
- fops: set to the v4l2_file_operations struct.
|
2008-12-19 06:20:22 -07:00
|
|
|
- ioctl_ops: if you use the v4l2_ioctl_ops to simplify ioctl maintenance
|
|
|
|
(highly recommended to use this and it might become compulsory in the
|
|
|
|
future!), then set this to your v4l2_ioctl_ops struct.
|
2009-03-13 07:03:04 -06:00
|
|
|
- parent: you only set this if v4l2_device was registered with NULL as
|
|
|
|
the parent device struct. This only happens in cases where one hardware
|
|
|
|
device has multiple PCI devices that all share the same v4l2_device core.
|
|
|
|
|
|
|
|
The cx88 driver is an example of this: one core v4l2_device struct, but
|
|
|
|
it is used by both an raw video PCI device (cx8800) and a MPEG PCI device
|
|
|
|
(cx8802). Since the v4l2_device cannot be associated with a particular
|
|
|
|
PCI device it is setup without a parent device. But when the struct
|
|
|
|
video_device is setup you do know which parent PCI device to use.
|
2008-12-19 06:20:22 -07:00
|
|
|
|
2008-12-23 09:42:25 -07:00
|
|
|
If you use v4l2_ioctl_ops, then you should set either .unlocked_ioctl or
|
|
|
|
.ioctl to video_ioctl2 in your v4l2_file_operations struct.
|
|
|
|
|
|
|
|
The v4l2_file_operations struct is a subset of file_operations. The main
|
|
|
|
difference is that the inode argument is omitted since it is never used.
|
2008-12-19 06:20:22 -07:00
|
|
|
|
|
|
|
|
|
|
|
video_device registration
|
|
|
|
-------------------------
|
|
|
|
|
|
|
|
Next you register the video device: this will create the character device
|
|
|
|
for you.
|
|
|
|
|
|
|
|
err = video_register_device(vdev, VFL_TYPE_GRABBER, -1);
|
|
|
|
if (err) {
|
2008-12-22 05:13:11 -07:00
|
|
|
video_device_release(vdev); /* or kfree(my_vdev); */
|
2008-12-19 06:20:22 -07:00
|
|
|
return err;
|
|
|
|
}
|
|
|
|
|
|
|
|
Which device is registered depends on the type argument. The following
|
|
|
|
types exist:
|
|
|
|
|
|
|
|
VFL_TYPE_GRABBER: videoX for video input/output devices
|
|
|
|
VFL_TYPE_VBI: vbiX for vertical blank data (i.e. closed captions, teletext)
|
|
|
|
VFL_TYPE_RADIO: radioX for radio tuners
|
|
|
|
VFL_TYPE_VTX: vtxX for teletext devices (deprecated, don't use)
|
|
|
|
|
|
|
|
The last argument gives you a certain amount of control over the device
|
2009-09-06 04:54:00 -06:00
|
|
|
device node number used (i.e. the X in videoX). Normally you will pass -1
|
|
|
|
to let the v4l2 framework pick the first free number. But sometimes users
|
|
|
|
want to select a specific node number. It is common that drivers allow
|
|
|
|
the user to select a specific device node number through a driver module
|
|
|
|
option. That number is then passed to this function and video_register_device
|
|
|
|
will attempt to select that device node number. If that number was already
|
|
|
|
in use, then the next free device node number will be selected and it
|
|
|
|
will send a warning to the kernel log.
|
|
|
|
|
|
|
|
Another use-case is if a driver creates many devices. In that case it can
|
|
|
|
be useful to place different video devices in separate ranges. For example,
|
|
|
|
video capture devices start at 0, video output devices start at 16.
|
2009-09-06 04:13:14 -06:00
|
|
|
So you can use the last argument to specify a minimum device node number
|
|
|
|
and the v4l2 framework will try to pick the first free number that is equal
|
2008-12-19 06:20:22 -07:00
|
|
|
or higher to what you passed. If that fails, then it will just pick the
|
|
|
|
first free number.
|
|
|
|
|
2009-09-06 04:54:00 -06:00
|
|
|
Since in this case you do not care about a warning about not being able
|
|
|
|
to select the specified device node number, you can call the function
|
|
|
|
video_register_device_no_warn() instead.
|
|
|
|
|
2008-12-19 06:20:22 -07:00
|
|
|
Whenever a device node is created some attributes are also created for you.
|
|
|
|
If you look in /sys/class/video4linux you see the devices. Go into e.g.
|
|
|
|
video0 and you will see 'name' and 'index' attributes. The 'name' attribute
|
2009-06-19 08:32:56 -06:00
|
|
|
is the 'name' field of the video_device struct.
|
2008-12-19 06:20:22 -07:00
|
|
|
|
2009-06-19 08:32:56 -06:00
|
|
|
The 'index' attribute is the index of the device node: for each call to
|
|
|
|
video_register_device() the index is just increased by 1. The first video
|
|
|
|
device node you register always starts with index 0.
|
2008-12-19 06:20:22 -07:00
|
|
|
|
|
|
|
Users can setup udev rules that utilize the index attribute to make fancy
|
|
|
|
device names (e.g. 'mpegX' for MPEG video capture device nodes).
|
|
|
|
|
|
|
|
After the device was successfully registered, then you can use these fields:
|
|
|
|
|
|
|
|
- vfl_type: the device type passed to video_register_device.
|
|
|
|
- minor: the assigned device minor number.
|
2009-09-06 04:13:14 -06:00
|
|
|
- num: the device node number (i.e. the X in videoX).
|
2009-06-19 08:32:56 -06:00
|
|
|
- index: the device index number.
|
2008-12-19 06:20:22 -07:00
|
|
|
|
|
|
|
If the registration failed, then you need to call video_device_release()
|
|
|
|
to free the allocated video_device struct, or free your own struct if the
|
|
|
|
video_device was embedded in it. The vdev->release() callback will never
|
|
|
|
be called if the registration failed, nor should you ever attempt to
|
|
|
|
unregister the device if the registration failed.
|
|
|
|
|
|
|
|
|
|
|
|
video_device cleanup
|
|
|
|
--------------------
|
|
|
|
|
|
|
|
When the video device nodes have to be removed, either during the unload
|
|
|
|
of the driver or because the USB device was disconnected, then you should
|
|
|
|
unregister them:
|
|
|
|
|
|
|
|
video_unregister_device(vdev);
|
|
|
|
|
|
|
|
This will remove the device nodes from sysfs (causing udev to remove them
|
|
|
|
from /dev).
|
|
|
|
|
|
|
|
After video_unregister_device() returns no new opens can be done.
|
|
|
|
|
|
|
|
However, in the case of USB devices some application might still have one
|
|
|
|
of these device nodes open. You should block all new accesses to read,
|
|
|
|
write, poll, etc. except possibly for certain ioctl operations like
|
|
|
|
queueing buffers.
|
|
|
|
|
|
|
|
When the last user of the video device node exits, then the vdev->release()
|
|
|
|
callback is called and you can do the final cleanup there.
|
|
|
|
|
|
|
|
|
|
|
|
video_device helper functions
|
|
|
|
-----------------------------
|
|
|
|
|
|
|
|
There are a few useful helper functions:
|
|
|
|
|
2009-11-27 09:56:50 -07:00
|
|
|
- file/video_device private data
|
|
|
|
|
2008-12-19 06:20:22 -07:00
|
|
|
You can set/get driver private data in the video_device struct using:
|
|
|
|
|
2009-02-07 03:07:04 -07:00
|
|
|
void *video_get_drvdata(struct video_device *vdev);
|
|
|
|
void video_set_drvdata(struct video_device *vdev, void *data);
|
2008-12-19 06:20:22 -07:00
|
|
|
|
|
|
|
Note that you can safely call video_set_drvdata() before calling
|
|
|
|
video_register_device().
|
|
|
|
|
|
|
|
And this function:
|
|
|
|
|
|
|
|
struct video_device *video_devdata(struct file *file);
|
|
|
|
|
|
|
|
returns the video_device belonging to the file struct.
|
|
|
|
|
2009-11-27 09:56:50 -07:00
|
|
|
The video_drvdata function combines video_get_drvdata with video_devdata:
|
2008-12-19 06:20:22 -07:00
|
|
|
|
|
|
|
void *video_drvdata(struct file *file);
|
|
|
|
|
|
|
|
You can go from a video_device struct to the v4l2_device struct using:
|
|
|
|
|
2008-12-23 08:17:23 -07:00
|
|
|
struct v4l2_device *v4l2_dev = vdev->v4l2_dev;
|
2009-02-14 03:29:07 -07:00
|
|
|
|
2009-11-27 09:56:50 -07:00
|
|
|
- Device node name
|
|
|
|
|
|
|
|
The video_device node kernel name can be retrieved using
|
|
|
|
|
|
|
|
const char *video_device_node_name(struct video_device *vdev);
|
|
|
|
|
|
|
|
The name is used as a hint by userspace tools such as udev. The function
|
|
|
|
should be used where possible instead of accessing the video_device::num and
|
|
|
|
video_device::minor fields.
|
|
|
|
|
|
|
|
|
2009-02-14 03:29:07 -07:00
|
|
|
video buffer helper functions
|
|
|
|
-----------------------------
|
|
|
|
|
2010-02-22 13:47:46 -07:00
|
|
|
The v4l2 core API provides a set of standard methods (called "videobuf")
|
|
|
|
for dealing with video buffers. Those methods allow a driver to implement
|
|
|
|
read(), mmap() and overlay() in a consistent way. There are currently
|
|
|
|
methods for using video buffers on devices that supports DMA with
|
|
|
|
scatter/gather method (videobuf-dma-sg), DMA with linear access
|
|
|
|
(videobuf-dma-contig), and vmalloced buffers, mostly used on USB drivers
|
|
|
|
(videobuf-vmalloc).
|
|
|
|
|
|
|
|
Please see Documentation/video4linux/videobuf for more information on how
|
|
|
|
to use the videobuf layer.
|