diff options
Diffstat (limited to 'Documentation/video4linux/v4l2-framework.txt')
| -rw-r--r-- | Documentation/video4linux/v4l2-framework.txt | 27 |
1 files changed, 24 insertions, 3 deletions
diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt index fe53177f0d3..e1e6a01d7ac 100644 --- a/Documentation/video4linux/v4l2-framework.txt +++ b/Documentation/video4linux/v4l2-framework.txt @@ -580,19 +580,25 @@ allocated memory. You should also set these fields: - v4l2_dev: set to the v4l2_device parent device. + - name: set to something descriptive and unique. + - fops: set to the v4l2_file_operations struct. + - 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. + - lock: leave to NULL if you want to do all the locking in the driver. Otherwise you give it a pointer to a struct mutex_lock and before any of the v4l2_file_operations is called this lock will be taken by the - core and released afterwards. + core and released afterwards. See the next section for more details. + - prio: keeps track of the priorities. Used to implement VIDIOC_G/S_PRIORITY. If left to NULL, then it will use the struct v4l2_prio_state in v4l2_device. If you want to have a separate priority state per (group of) device node(s), then you can point it to your own struct v4l2_prio_state. + - 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. @@ -602,6 +608,7 @@ You should also set these fields: (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. + - flags: optional. Set to V4L2_FL_USE_FH_PRIO if you want to let the framework handle the VIDIOC_G/S_PRIORITY ioctls. This requires that you use struct v4l2_fh. Eventually this flag will disappear once all drivers use the core @@ -634,8 +641,22 @@ v4l2_file_operations and locking -------------------------------- You can set a pointer to a mutex_lock in struct video_device. Usually this -will be either a top-level mutex or a mutex per device node. If you want -finer-grained locking then you have to set it to NULL and do you own locking. +will be either a top-level mutex or a mutex per device node. By default this +lock will be used for each file operation and ioctl, but you can disable +locking for selected ioctls by calling: + + void v4l2_dont_use_lock(struct video_device *vdev, unsigned int cmd); + +E.g.: v4l2_dont_use_lock(vdev, VIDIOC_DQBUF); + +You have to call this before you register the video_device. + +Particularly with USB drivers where certain commands such as setting controls +can take a long time you may want to do your own locking for the buffer queuing +ioctls. + +If you want still finer-grained locking then you have to set mutex_lock to NULL +and do you own locking completely. It is up to the driver developer to decide which method to use. However, if your driver has high-latency operations (for example, changing the exposure |