diff options
Diffstat (limited to 'Documentation/video4linux/v4l2-framework.txt')
-rw-r--r-- | Documentation/video4linux/v4l2-framework.txt | 38 |
1 files changed, 35 insertions, 3 deletions
diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt index 7de55cf..0627081 100644 --- a/Documentation/video4linux/v4l2-framework.txt +++ b/Documentation/video4linux/v4l2-framework.txt @@ -71,6 +71,10 @@ sub-device instances, the video_device struct stores V4L2 device node data and in the future a v4l2_fh struct will keep track of filehandle instances (this is not yet implemented). +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 ------------------ @@ -84,11 +88,14 @@ You must register the device instance: 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 use the media -device framework in addition to the V4L2 framework need to set +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. +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 @@ -530,6 +537,21 @@ If you use v4l2_ioctl_ops, then you should set either .unlocked_ioctl or 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. +If integration with the media framework is needed, you must initialize the +media_entity struct embedded in the video_device struct (entity field) by +calling media_entity_init(): + + struct media_pad *pad = &my_vdev->pad; + int err; + + err = media_entity_init(&vdev->entity, 1, pad, 0); + +The pads array must have been previously initialized. There is no need to +manually set the struct media_entity type and name fields. + +A reference to the entity will be automatically acquired/released when the +video device is opened/closed. + v4l2_file_operations and locking -------------------------------- @@ -559,6 +581,9 @@ for you. return err; } +If the v4l2_device parent device has a non-NULL mdev field, the video device +entity will be automatically registered with the media device. + Which device is registered depends on the type argument. The following types exist: @@ -634,6 +659,13 @@ release, of course) will return an error as well. 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. +Don't forget to cleanup the media entity associated with the video device if +it has been initialized: + + media_entity_cleanup(&vdev->entity); + +This can be done from the release callback. + video_device helper functions ----------------------------- |