diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/video4linux/v4l2-framework.txt | 120 |
1 files changed, 87 insertions, 33 deletions
diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt index f2df31b..1c8d449 100644 --- a/Documentation/video4linux/v4l2-framework.txt +++ b/Documentation/video4linux/v4l2-framework.txt @@ -549,6 +549,10 @@ You should also set these fields: 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. +- 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. @@ -559,8 +563,10 @@ You should also set these fields: 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. -If you use v4l2_ioctl_ops, then you should set either .unlocked_ioctl or -.ioctl to video_ioctl2 in your v4l2_file_operations struct. +If you use v4l2_ioctl_ops, then you should set .unlocked_ioctl to video_ioctl2 +in your v4l2_file_operations struct. + +Do not use .ioctl! This is deprecated and will go away in the future. 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. @@ -753,39 +759,24 @@ struct v4l2_fh -------------- struct v4l2_fh provides a way to easily keep file handle specific data -that is used by the V4L2 framework. Using v4l2_fh is optional for -drivers. +that is used by the V4L2 framework. New drivers must use struct v4l2_fh +since it is also used to implement priority handling (VIDIOC_G/S_PRIORITY). The users of v4l2_fh (in the V4L2 framework, not the driver) know whether a driver uses v4l2_fh as its file->private_data pointer by -testing the V4L2_FL_USES_V4L2_FH bit in video_device->flags. - -Useful functions: - -- v4l2_fh_init() - - Initialise the file handle. This *MUST* be performed in the driver's - v4l2_file_operations->open() handler. - -- v4l2_fh_add() +testing the V4L2_FL_USES_V4L2_FH bit in video_device->flags. This bit is +set whenever v4l2_fh_init() is called. - Add a v4l2_fh to video_device file handle list. May be called after - initialising the file handle. - -- v4l2_fh_del() - - Unassociate the file handle from video_device(). The file handle - exit function may now be called. +struct v4l2_fh is allocated as a part of the driver's own file handle +structure and file->private_data is set to it in the driver's open +function by the driver. -- v4l2_fh_exit() +In many cases the struct v4l2_fh will be embedded in a larger structure. +In that case you should call v4l2_fh_init+v4l2_fh_add in open() and +v4l2_fh_del+v4l2_fh_exit in release(). - Uninitialise the file handle. After uninitialisation the v4l2_fh - memory can be freed. - -struct v4l2_fh is allocated as a part of the driver's own file handle -structure and is set to file->private_data in the driver's open -function by the driver. Drivers can extract their own file handle -structure by using the container_of macro. Example: +Drivers can extract their own file handle structure by using the container_of +macro. Example: struct my_fh { int blah; @@ -802,15 +793,21 @@ int my_open(struct file *file) ... + my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL); + + ... + ret = v4l2_fh_init(&my_fh->fh, vfd); - if (ret) + if (ret) { + kfree(my_fh); return ret; + } - v4l2_fh_add(&my_fh->fh); + ... file->private_data = &my_fh->fh; - - ... + v4l2_fh_add(&my_fh->fh); + return 0; } int my_release(struct file *file) @@ -819,8 +816,65 @@ int my_release(struct file *file) struct my_fh *my_fh = container_of(fh, struct my_fh, fh); ... + v4l2_fh_del(&my_fh->fh); + v4l2_fh_exit(&my_fh->fh); + kfree(my_fh); + return 0; } +Below is a short description of the v4l2_fh functions used: + +int v4l2_fh_init(struct v4l2_fh *fh, struct video_device *vdev) + + Initialise the file handle. This *MUST* be performed in the driver's + v4l2_file_operations->open() handler. + +void v4l2_fh_add(struct v4l2_fh *fh) + + Add a v4l2_fh to video_device file handle list. Must be called once the + file handle is completely initialized. + +void v4l2_fh_del(struct v4l2_fh *fh) + + Unassociate the file handle from video_device(). The file handle + exit function may now be called. + +void v4l2_fh_exit(struct v4l2_fh *fh) + + Uninitialise the file handle. After uninitialisation the v4l2_fh + memory can be freed. + + +If struct v4l2_fh is not embedded, then you can use these helper functions: + +int v4l2_fh_open(struct file *filp) + + This allocates a struct v4l2_fh, initializes it and adds it to the struct + video_device associated with the file struct. + +int v4l2_fh_release(struct file *filp) + + This deletes it from the struct video_device associated with the file + struct, uninitialised the v4l2_fh and frees it. + +These two functions can be plugged into the v4l2_file_operation's open() and +release() ops. + + +Several drivers need to do something when the first file handle is opened and +when the last file handle closes. Two helper functions were added to check +whether the v4l2_fh struct is the only open filehandle of the associated +device node: + +int v4l2_fh_is_singular(struct v4l2_fh *fh) + + Returns 1 if the file handle is the only open file handle, else 0. + +int v4l2_fh_is_singular_file(struct file *filp) + + Same, but it calls v4l2_fh_is_singular with filp->private_data. + + V4L2 events ----------- |