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Diffstat (limited to 'Documentation/media/kapi/v4l2-framework.rst')
| -rw-r--r-- | Documentation/media/kapi/v4l2-framework.rst | 139 |
1 files changed, 0 insertions, 139 deletions
diff --git a/Documentation/media/kapi/v4l2-framework.rst b/Documentation/media/kapi/v4l2-framework.rst index 740875ddfcec..1fdc96bd7411 100644 --- a/Documentation/media/kapi/v4l2-framework.rst +++ b/Documentation/media/kapi/v4l2-framework.rst @@ -80,145 +80,6 @@ The V4L2 framework also optionally integrates with the media framework. If a driver sets the struct v4l2_device mdev field, sub-devices and video nodes will automatically appear in the media framework as entities. - -struct v4l2_device ------------------- - -Each device instance is represented by a struct v4l2_device (v4l2-device.h). -Very simple devices can just allocate this struct, but most of the time you -would embed this struct inside a larger struct. - -You must register the device instance: - -.. code-block:: none - - v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev); - -Registration will initialize the v4l2_device struct. If the dev->driver_data -field is NULL, it will be linked to v4l2_dev. - -Drivers that want integration with the media device framework need to set -dev->driver_data manually to point to the driver-specific device structure -that embed the struct v4l2_device instance. This is achieved by a -dev_set_drvdata() call before registering the V4L2 device instance. They must -also set the struct v4l2_device mdev field to point to a properly initialized -and registered media_device instance. - -If v4l2_dev->name is empty then it will be set to a value derived from dev -(driver name followed by the bus_id, to be precise). If you set it up before -calling v4l2_device_register then it will be untouched. If dev is NULL, then -you **must** setup v4l2_dev->name before calling v4l2_device_register. - -You can use v4l2_device_set_name() to set the name based on a driver name and -a driver-global atomic_t instance. This will generate names like ivtv0, ivtv1, -etc. If the name ends with a digit, then it will insert a dash: cx18-0, -cx18-1, etc. This function returns the instance number. - -The first 'dev' argument is normally the struct device pointer of a pci_dev, -usb_interface or platform_device. It is rare for dev to be NULL, but it happens -with ISA devices or when one device creates multiple PCI devices, thus making -it impossible to associate v4l2_dev with a particular parent. - -You can also supply a notify() callback that can be called by sub-devices to -notify you of events. Whether you need to set this depends on the sub-device. -Any notifications a sub-device supports must be defined in a header in -include/media/<subdevice>.h. - -You unregister with: - -.. code-block:: none - - v4l2_device_unregister(struct v4l2_device *v4l2_dev); - -If the dev->driver_data field points to v4l2_dev, it will be reset to NULL. -Unregistering will also automatically unregister all subdevs from the device. - -If you have a hotpluggable device (e.g. a USB device), then when a disconnect -happens the parent device becomes invalid. Since v4l2_device has a pointer to -that parent device it has to be cleared as well to mark that the parent is -gone. To do this call: - -.. code-block:: none - - v4l2_device_disconnect(struct v4l2_device *v4l2_dev); - -This does *not* unregister the subdevs, so you still need to call the -v4l2_device_unregister() function for that. If your driver is not hotpluggable, -then there is no need to call v4l2_device_disconnect(). - -Sometimes you need to iterate over all devices registered by a specific -driver. This is usually the case if multiple device drivers use the same -hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv -hardware. The same is true for alsa drivers for example. - -You can iterate over all registered devices as follows: - -.. code-block:: none - - static int callback(struct device *dev, void *p) - { - struct v4l2_device *v4l2_dev = dev_get_drvdata(dev); - - /* test if this device was inited */ - if (v4l2_dev == NULL) - return 0; - ... - return 0; - } - - int iterate(void *p) - { - struct device_driver *drv; - int err; - - /* Find driver 'ivtv' on the PCI bus. - pci_bus_type is a global. For USB busses use usb_bus_type. */ - drv = driver_find("ivtv", &pci_bus_type); - /* iterate over all ivtv device instances */ - err = driver_for_each_device(drv, NULL, p, callback); - put_driver(drv); - return err; - } - -Sometimes you need to keep a running counter of the device instance. This is -commonly used to map a device instance to an index of a module option array. - -The recommended approach is as follows: - -.. code-block:: none - - static atomic_t drv_instance = ATOMIC_INIT(0); - - static int drv_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id) - { - ... - state->instance = atomic_inc_return(&drv_instance) - 1; - } - -If you have multiple device nodes then it can be difficult to know when it is -safe to unregister v4l2_device for hotpluggable devices. For this purpose -v4l2_device has refcounting support. The refcount is increased whenever -video_register_device is called and it is decreased whenever that device node -is released. When the refcount reaches zero, then the v4l2_device release() -callback is called. You can do your final cleanup there. - -If other device nodes (e.g. ALSA) are created, then you can increase and -decrease the refcount manually as well by calling: - -.. code-block:: none - - void v4l2_device_get(struct v4l2_device *v4l2_dev); - -or: - -.. code-block:: none - - int v4l2_device_put(struct v4l2_device *v4l2_dev); - -Since the initial refcount is 1 you also need to call v4l2_device_put in the -disconnect() callback (for USB devices) or in the remove() callback (for e.g. -PCI devices), otherwise the refcount will never reach 0. - struct v4l2_subdev ------------------ |