diff options
Diffstat (limited to 'Documentation/video4linux/v4l2-framework.txt')
| -rw-r--r-- | Documentation/video4linux/v4l2-framework.txt | 35 |
1 files changed, 29 insertions, 6 deletions
diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt index e831aaca66f8..f22f35c271f3 100644 --- a/Documentation/video4linux/v4l2-framework.txt +++ b/Documentation/video4linux/v4l2-framework.txt @@ -44,8 +44,8 @@ All drivers have the following structure: 2) A way of initializing and commanding sub-devices (if any). -3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX, /dev/radioX and - /dev/vtxX) and keeping track of device-node specific data. +3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX and /dev/radioX) + and keeping track of device-node specific data. 4) Filehandle-specific structs containing per-filehandle data; @@ -192,6 +192,11 @@ 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. @@ -448,6 +453,10 @@ You should also set these fields: - 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. - 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. @@ -464,6 +473,22 @@ 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. +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. + +If a lock is specified then all file operations will be serialized on that +lock. If you use videobuf then you must pass the same lock to the videobuf +queue initialize function: if videobuf has to wait for a frame to arrive, then +it will temporarily unlock the lock and relock it afterwards. If your driver +also waits in the code, then you should do the same to allow other processes +to access the device node while the first process is waiting for something. + +The implementation of a hotplug disconnect should also take the lock before +calling v4l2_device_disconnect. video_device registration ------------------------- @@ -483,7 +508,6 @@ 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 device node number used (i.e. the X in videoX). Normally you will pass -1 @@ -547,9 +571,8 @@ 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. So after the unregister all file operations will return -an error as well, except for the ioctl and unlocked_ioctl file operations: -those will still be passed on since some buffer ioctls may still be needed. +device nodes open. So after the unregister all file operations (except +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. |